wiip^^^^^^^^^ .'i'iA' iMi The original of tiiis bool< is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924080066537 UNIVERSITY UBRAfjV mwmm^ 080 066 537 DATE DUE GAYLORD PRINTED IN U.S.A Production Note Cornell University Library produced this volume to replace the irreparably deteriorated original . It was scanned using Xerox software and equipment at 600 dots per inch resolution and compressed prior to storage using ITU Group 4 compression. The digital data were used to create Cornell ' s replacement volume on paper that meets the ANSI Standard Z39. 48-1992. The production of this volume was supported by the National Endowment for the Humanities. Digital file copyright by Cornell University Library 1995. Scanned as part of the A. R. Mann Library project to preserve and enhance access to the Core Historical Literature of the Agricultural Sciences. Titles included in this collection are listed in the volumes published by the Cornell University Press in the series THE LITERATURE OF THE AGRICULTURAL SCIENCES, 1991-1996, Wallace C. Olsen, series editor. ALBERT R. MANN LIBRARY New York State Colleges OF Agriculture and Home Economics Cornell University DISEASES OF GREENHOUSE CROPS AND THEIR CONTROL OTHER WORKS BY THE SAME AUTHOR The Culture and Diseases of the Sweet Pea - $2.50 net niustrated Diseases of Truck Crops and Their Control - $5.00 net niustrated Diseases of the Sweet Potato Qn Preparatioii) E. P. DUTTON & COMPANY NEW YORK DISEASES OF GREENHOUSE CROPS AND THEIR CONTROL BY J. J. TAUBENHAUS, Ph.D. Chief of the Division of Plant Pathology and Physiology. Texas Agii rjltural Experiment Station, Agricultural and Mechanical College of Texas Author of "The Culture and Diseases of the Sweet Pea" "Truck Crop Diseases and their Control" NEW YORK E. p. BUTTON & COMPANY 68 1 FIFTH AVENUE !Copyright, 1920, B» E. P. DUTTON & COMPANY Au Rights Reserved PSINTED IN THE UIOTED STATES OF AHEKICA THIS BOOK IS AFFECTIONATELY DEDICATED TO MY WIFE INTRODUCTION The art of forcing vegetables and flowers is not a new one ; however, its economic aspect is of modem origin. The Thirteenth Census of the United States estimates that the total area of land under glass in 1909 was 114,655,000 square feet, of which 105,166,000 square feet were in greenhouses and 9,490,000 feet were covered by sashes and frames. About 99% of the value of the plants and flowers in 1909 was produced in 7,444 establishments, the average value of each of these establishments be- ing $4,630.00. As is natural to expect, these estab- lishments were located near large cities. The lead- ing states in value of forced flowers and plants were New York with $5,110,000; Pennsylvania with $3,761,000; Illinois with $3,681,000; New Jersey with $2,839,000; Massachusetts with $2,432,000; Ohio with $2,357,000; California with $1,374,000; Indiana with $1,202,000; Michigan with $1,132,- 000; and Connecticut with $1,042,000. States with less than a million are not here recorded. The total value of forced plants and flowers as estimated for 1909 was $24,930,000. There are as yet no available figures of the area and the money value of the greenhouse industry. It is, however, reasonable to suppose that the num- vii viii Introduction ber of establishments and their money value have lately increased by at least fifty per cent. This, therefore, represents a vast sum of money and an important industry of the United States which can- not be ignored. Plants under greenhouse culture are far from being subjected to normal conditions. The expres- sion "tender as a hothouse plant" well expresses the truth. Because of this fact greenhouse plants are naturally more susceptible to diseases indoors than similar plants grown in the open. This at once emphasizes the importance of studying the diseases of greenhouse crops with a view to furnishing the growers such information as may help them to re- duce important plant diseases and thereby increase their profits. We have as yet no available figures as to the money losses from diseases of greenhouse crops. A conservative estimate, however, may place these losses at about thirty per cent. The literature on diseases of greenhouse crops in the United States is rather fragmentary and scat- tered. The American Plant Pathologists have been too busy in devoting much time to the investigations of the diseases of cereals, fruit and truck crops. Considering that plant pathology is only a new sci- ence, the diseases of the greenhouse crops had of ne- cessity to be neglected. It is, therefore, the aim and purpose of the present volume to bring together available information on the subject and to place it at the disposal of the greenhouse men. The author realizes too well the incompleteness of this work; Introduction ix however, it is felt that no apologies are due and it is hoped that it will meet an important demand for infonnation, and stimulate further research in this line. The book is intended as a guide to practical growers, teachers, students and investigators in plant pathology. It is taken for granted that the practical man who uses this volume will study it with a view to gathering information to serve him as a guide, as no definite hard rules are here laid down which could apply to the problems of each individual case. It is only by combining the information with good common sense that the best results are to be ob- tained. Constructive criticism is solicited and help- ful suggestions will be gratefully received. Acknowledgments are here due to Dr. and Mrs. D. de Sola Pool of New York City; Dr. I. Adler- blum. Statistician of the Metropolitan Life Insur- ance Company, New York City; Professor R. B. Brackett, Professor of English of the Texas A. and M. College; Professor S. C. Hoyle, Editor Exten- sion Service Publicaticm, Texas A. and M. College, for helpful criticisms and for reading the manu- script and proofs; to Professor F. B. Paddock, Entomologist, Texas A. and M. Agricultural Ex- periment Statical, for reading the proofs; Miss Florence Buckman of the Plant Pathology Divi- sion, Texas Experiment Station for assistance in preparing the glossary and the index. Grateful acknowledgments are further due to Dr. C. G. Hopkins for fig. 2a, Dr. T. F. Maims for fig. 2b, Professor L. Green for fig. 5a, Professor L. X Introduction E. Melchers for figs. 8a, b, and c, Dr. Clinton for figs. i6b, 38a and 40b, Professor R. E. Smith for fig. 22, Miss Nelly Brown for fig. 26, Professor A. D. Selby for fig. 28a, Professor Edson for fig. 35, Professor H. E. Stevens for figs. 37a and b, Profes- sor H. S. Jackson for fig. 40a, Professor L. N. Mas- sey for figs. 65b and 66a, Dr. A. B. Stout for fig. 72a, Professor Moznette for figs. 78c and d. The King Construction Company for figs. 25 and 45, The John Moninger Greenhouse Company for fig. 52, Professor F. B. Paddock for figs. 80 and 81. Credit is also due to the Foley Greenhouse Manu- facturing Company for figs. 21, 49, 57a, 58a, 60 and 64. The remainder of the borrowed figures are acknowledged in their proper places. The author also wishes to express his indebtedness to the Texas Agricultural Experiment Station for the original fig- ures which were taken by the Station Photographer for the Division of Plant Pathology and Physiology. J. J. Taubenhaus College Station, Texas May 1, 1919 CONTENTS PART I CHAPTER PAGE I. The Healthy Soil 3 II. Sick Soils 16 III. Treatment of Sick Soils .... 28 PART II CULTURAL CONSIDERATIONS TV. Light in Its Relation to Greenhouse Culture 53 V. Moisture and Water Requirements 73 VI. Breaking the Rest Period of Plants 86 PART III diseases of greenhouse vegetables VII. Nature of Plant Diseases • • . 93 VIII. Germination Troubles 104 IX. Beet Diseases 114 X. Cauliflower Diseases 122 XI. Cucumber Diseases 133 XII. Lettuce Diseases 145 XIII. Mushroom Diseases 159 XIV. Parsley Diseases 166 XV. Radish Diseases 173 XVI. Tomato Diseases 180 xii Contents PART IV DISEASES OF ORNAMENTALS CHAPTER PAGE XVII. Alternanthera Diseases .... 200 XVIII. Aster Diseases 207 XIX. Carnation Diseases 21 ? XX. Chrysanthemum Diseases . . . . 23 ~ XXI. Cyclamen Diseases 24^- XXII. Hyacinth Diseases 266 XXIII. Lilac Diseases 275 XXIV. Orchid Diseases 29c XXV. Primrose Diseases 315 XXVI. Sweet Pea Diseases 33/! XXVII. Tulip Diseases 34F PART V greenhouse fests XXVIII. Plant Pests 364 XXIX. Greenhouse Thrips 36c PART VI METHODS OF CONTROL XXX. Methods of Control 381 LIST OF ILLUSTRATIONS MGTJSE FACING PAGE 1. Effect of Fertilizers and Watering on the Yield of Lettuce 5 2. Effect of a Balanced Fertilizer on Corn and Clover 9 3. Conidiophore and Conidia of Pythium . . 19 4. Nematode 25 5. Leaf Blight Nematode 27 6. Steam Sterilization Apparatus 37 7. Effect of Soil Sterilization 39 8. Melcher's Soil Sterilizer 43 9. Action of Different Light Rays on Coleus and on Lettuce 63 10. Action of Different Light Rays on the Color of Plants 65 11. Sling Psychrometer 77 12. Effect of Subirrigation on Lettuce .... 85 13. Effect of Etherization on Plants .... 87 14. Effect of Etherization on Hybiscus syriacus . 89 15. Bean Diseases iii 16. Beet Diseases 115 17. Cauliflower Disease 123 18. Celery Disease 131 19. Celery Disease 133 20. Young Healthy Greenhouse Cucumber Plants 135 21. Cucumber Diseases 137 22. Cucumber Root Knot 141 23. Egg Plant Diseases 143 24. Egg Plant Diseases 145 xiii xiv List of Illustrations HGUBE FACING PAGE 25. Type of Lettuce House 147 26. Lettuce Diseases 149 27. Lettuce Diseases 151 28. Lettuce Diseases 153 29. Typical Muskmelon House 155 30. Muskmelon Diseases 157 31. Root Knot of Muskmelon IS9 32. Healthy Mushroom Bed 161 33. Sclerotinia Rot on Pea Pods 167 34. Pepper Diseases 169 35- Rheosporangium Rot on Radish .... 175 36. Tomato Diseases 193 37. Tomato Diseases 194 38. Tomato Diseases 195 39. Effect ofFumigation on Tomatoes .... 197 40. Anthirrhinum Diseases 203 41. Anthirrhinum Diseases 205 42. Aster Diseases 209 43. Begonia Root Knot 213 44. Calceolaria Leaf Blight 215 45. Type of Carnation House 217 46. Carnation Diseases 223 47. Carnation Diseases 227 48. Carnation Diseases 229 49. Type of Chrysanthemum House . . . .235 50. Chrysanthemum Diseases 237 51. Broom Rope of Coleus 245 52. Type of Cyclamen House 249 53. Dracena Diseases 251 54. Fern Yellows 255 55. Fern Diseases 257 56. Geranium Diseases 261 57. Hyacinth Diseases 267 58. Lily Diseases 277 List of Illustrations xv FIGUSE TACINO PAGE 59. Orchid Diseases 295 60. Type of Palm House 307 61. Palm Diseases 309 62. Pansy Diseases 311 63. Primrose Diseases 315 64. Rose House 319 65. Rose Diseases 321 66. Rose Diseases 325 67. Rose Diseases 329 68. Rubber Plant and Schizanthus Diseases . . 331 69. Sweet Pea Diseases 335 70. Sweet Pea Diseases 341 71. Sweet Pea Diseases 347 72. Tulip Diseases 349 73. Violet Diseases 355 74. Violet Diseases 357 75. Violet Diseases 359 76. Red Spider 365 77. Mite Injury of Geranium and Cyclamen . . 367 78. Snapdragon Mite Injury 369 79. Snapdragon and Geranium Mite Injury . . 370 80. Plant Aphids 37^ 81. Bucket Spray Pump 407 82. Violet Cuttings 409 PART I CHAPTER 1 THE HEALTHY SOIL An intelligent understanding of the soil is of para- mount importance to the success of the greenhouse. There are three important points that we must con- sider in the study of a healthy soil. They arc : ( i ) texture, (2) fertilizers, (3) soil flora. Texture Texture deals with the character of the particles which make up a soil, and with their arrangement in relation to each other. Clay soils arc generally made up of very minute particles. Silt is made up of large grains. Coarse sand or gravel is composed of the largest grains. A soil is said to be porous when air or water can circulate through it freely. The porosity depends on the various proportions of clay, silt and sand which that soil contains. Plant growth, and incidentally plant health, is closely in- terwoven with the soil structure. Compact, sticky clays will be far more unfavorable to greenhouse crops than a clay loam. The greenhouse man has the advantage over the ordinary farmer because he can modify the texture 3 4 Diseases of Greenhouse Crops of his soil so as to make it ideal for his crops. By c(Mnbining the proper amounts of clay, silt, sand and humus, he may give to the plants a most congenial place to thrive in. To obtain such a result the gar- dener must exercise his best judgment. By varying the texture of the soil we may often influence the plants unfavorably. Flowering plants may be made to produce excessive foliage and few blossoms, while others may be differently affected. Fertilizers Crops require certain food elements to make growth possible at all, and they further require spe- cific substances to enable them to accomplish definite purposes. The carnation, for instance, requires pe- culiar food elements to attain maximum growth. It further requires special nutritive elements to enable it to produce flowers and to avoid going altogether to foliage. The four leading plant foods needed by greenhouse crops are nitrogen, phosphorus, potassium and lime. All the other plant food elements are present in nearly all soils. The effect of nitrogen is to stimulate leaf and stem growth, and to add green color. An overdose of it, however, may result in soft plant tissue, and thus retard fruiting. Acid phosphate stimulates root growth, and an overdose of it encourages an excess of root formation over foliage. Phosphorus also stimulates earliness in fruiting. The effect of potas- sium is to help the plant in assimilating other plant 1 H 1 j-14-H 1 1 11 ;i;;;:;IS: :;»:: :; :: s:l •! s! if :: :: M-i«-U» ^ P --^ g5 ■S ii s •= ^ « ^1^ s-s-s I M ;!^l s,a8 J- °i. «o"S i 111 111 HE YiEL Sulphate Sulphate III SSgSgSg ojtomaiMaiM r ,^ -D O-a c^ «•« ^Ssi ^fi O H H a f. 5 fn a K <: . o> U-i O O ii u 3 tn S £! B S^ •a 1 i 1 1 s o ^4 O o Effect o ica\ fertilis soil u 1 Is u g s ^•S-3 s|, F ss -aSE ajS i S S .-"IH gg §11 feO* S^ s ^^ Hi •25 «< O K» OMK •a »>ti i*a.^ The Healthy Soil 5 food, and indirectly in the manufacture of starch. It also encourages the production of finer plant tis- sue, thus increasing the plant's resistance to disease. The aim of the greenhouse man is to produce early truck crops or cut flowers and this is directly con- cerned with feeding. Because the four plant food elements above mentioned are of extreme impor- tance, their application cannot be indiscriminate. The greenhouse man must know how much of them to use in combination or separately. He must know also which element will especially benefit the par- ticular crop with which he deals. In his investiga- tions with the fertilizer requirements of lettuce, Stuart * reached the following conclusions : Potash when used in any considerable amount either alone or with nitrate of soda is unfavorable for growth (fig. 1, D.). Acid phosphate alone, in combination with nitrate of soda, or in combination with muriate of potash, stimulates growth (fig. i. A, B, C). For lettuce the use of chemical fertilizers proved slightly superior to stable manure, while nitrate of soda was found to be superior to dried blood. Wheeler and AdamSjf in their work with radishes, found that an application of partially composted horse manure at the rate of 75 tons per acre gave better results than any other combination of fertilizers used. Work- ing with carnations. Darner + and his associates • Stuart W., Indiana Agr. Expt. Sta. Bui. 84, Vol. 10: 115-142, ^900. t Wheeler, H. J., and Adams, G. E., Rhode Island Agr. Expt. Sta. Bui. 128: 183-194, 1908. i: Darner, H. B., et al., Illinois Agr. Expt. Sta. Bui. 176: 365- 386, 1914. 6 Diseases of Greenhouse Crops found that the use of nitrogen and acid phosphate caused an increase in the quantity and quality of the blossoms, but that the excessive use of potassium sulphate and dried blood would act injuriously on the plants. In his work on roses, Muncic * conclud- ed that nitrogen in the form of farm manure, liquid manure or blood is very beneficial. The same seems also to be true for acid phosphate when used at the rate of 4 to 8 tons per acre. Lime should be added only when necessary to sweeten the soil. In this case, finely ground limestone may be used as a top dress- ing at the rate of 10 pounds per 100 square feet of bench space. From the above discussion, it is evident that the proper handling of fertilizers underlies the success or failure of greenhouse crops. The cattleman, the poultryman, and others who deal with live stock now fully appreciate the importance of a properly balanced ration. Plants are similarly living organ- isms and consequently they too derive most benefit from a balanced ration (fig. 1, A.). Aside from a consideration of the relation of the fertilizer to plant growth, its relationship to the soil must not be overlooked. Certain fertilizers, such as nitrate of soda, yield a residue of sodium, the accumulation of which sweetens the soil, and in the long run makes it alkaline. In clay soils serious physical effects may be the consequence. On the other hand, muriate and sulphate of potash, and sulphate of ammonia leave an acid residuum, the *Muncie, F. W., Illinois Agr. Expt. Sta. Bui. 196: 5x1-5(4, (917. The Healthy Soil 7 accumulation of which may render the soil sour. It therefore becomes imperative to so use or to so mix these fertilizers that their residues will combine and thus neutralize each other. One reason perhaps why greenhouse men favor the use of manure is that they have experienced the bad effects of the residue of improperly mixed fertilizers. Soil Flora By a soil flora is meant the bacteria or fungi, whether beneficial or harmful, which thrive in that soil. Science has proved definitely that a soil can no longer be regarded as a conglomeration of dead, inert particles of rock. The soil teems with life which to a large extent determines its fertility. The more numerous the beneficial bacteria and fungi it contains, the more fertile it will be. On the other hand if the beneficial micro-organisms are absent, or perform their work imperfectly, or if the soil is overridden by harmful parasitic bacteria or fungi, we speak of it as a sterile or sick soil. In the green- house, the soil flora is often entirely different from what it is outdoors. This is due to the fact that the soil is artificially made up of a mixture of various ingredients with the object of making it ideal for plant growth. It is imperative that the greenhouse manager possess some knowledge of bacteria and fungi, and that he understand the functions and the requirements of the soil micro-organisms, if he wishes 8 Diseases of Greenhouse Crops to secure proper control of his soil and to make it ideal for plant growth. A. Bacteria. Bacteria are minute microscopical plants that consist of a single cell. They are com- posed of a cell wall of protoplasm and average about 1/25000 of an inch in length. These simple organ- isms multiply by fission, that is, the original mother cell divides in two equal parts, which may separate or remain united, giving the appearance of a thread. It has been estimated that a single bacterium divides about every twenty minutes. Granting that this rate of division is uninterrupted for twenty-four hours, the descendants of a single one within a day would be in round numbers 1,800,999 trillions. These when placed end to end would make a string two trillion miles long, or a thread long enough to go around the earth at the equator 70,000,000 times. However, multiplication at such a rate cannot occur because food conditions are restricted. The three main types of bacteria are: 1. the cocci, 2. the ba- cilli or rods, 3. the spirilla or spirals (fig. 2, c). The greater number of the soil bacteria are benefi- cial, the most common being the saprophytes, or those which help to decay the dead organic matter from either animal or plant. The parasites on the other hand are those which produce disease. B. Fungi. Fungi are low forms of microscopic plants, of a slightly higher type than bacteria. Fungi are made up of colorless feeding threads technically known as hyphae or mycelium. The spores which correspond to the seed of the higher plants are borne Fig. 2. . ■ o. Effect of a balanced fertilizer on corn and clover, b. various organisms isolated from a soil particle, c. types of bacteria. Coccus, Bacillus and Spirilla I*"?''.,,?- E. Brown); d. pycnidium (after C. L. Shear), e. conidiophores of Penicillium. "^ The Healthy Soil 9 either in sacs, known as pycnidia (fig. 2, d) or on free stalks, known as conidiophores, meaning stalk bearing spores (fig. 2, e.). Fungi, like bacteria, de- pend on animals or plants for their food. Like bac- teria, they are differentiated into saprophytes and parasites. Relationship of Micro-organisms to the Fertility of a Soil Bacteriologists are c(HitinualIy engaged in discov- ering the possible function of numerous groups of the soil organisms. A recent exhaustive study * of Acti- ncanyces, or thread bacteria, in the soil, for instance, seems to show that they serve to decanpose grass roots, being more mnnerous in sod than in cultivated land. Other groups of bacteria undoubtedly per^ form other important functitms. The mere presence of friendly micro-organisms in the soil, however, would be insufficient to assure the welfare of our cultivated lands. These minute or- ganisms must find the conditions necessary to induce a maximum activity in the performance of their work, which is to act as chief cook in the dietary of the plant. Most of the plant's food, as it is found in the soil, is in a crude and unavailable form. The bits of mineral matter, the manure, or fertilizer added to the greenhouse soil, all craitain plant foods, but in a form which plants cannot readily •Conn, Joe! H., New Yo^ (Geneva), Agr. Expt. Sta. BdL 52: 3-11, 1916. 10 Diseases of Greenhouse Crops use. They must be softened and predigested, and this work is done by the friendly micro-organisms. The supply of plant food is therefore directly de- pendent on the work of these minute scavengers. An intimate relation exists between the higher and the lower form of plant life, the one depending on the other for sustenance. A. Number of Micro-organisms in Soil. In- vestigations by Waksman * and others clearly show that micro-organisms are present in soils everywhere (see Table I and fig. 2, b). It should be remembered that differences in the physical and chemical nature of the greenhouse soil, the sort of fertilizers used and the amount of tem- perature and moisture will all be important factors in determining the number of micro-organisms pres- ent. Nature and Function of a Healthy Soil Flora The function of a noimal soil is to provide avail- able plant food. About 95 per cent of the weight of a growing plant is made up of carbon, hydrogen, oxygen and nitrogen. The remaining 5 per cent constitutes the mineral or the non-combustible part or ash of the plant. Carbon, hydrogen, and oxygen are absorbed in the form of carbonic acid and water; nitrogen is usually derived from nitrates produced by micro-organisms out oi organic matter in the soil. Neither the organic nor the mineral elements are in 'Waksman, L. A., Soil Sdence, 3: 565-589, 1917. The Healthy Soil II Table i Bacteria Source of Soa Used Actinomyces or Thread Bacteria Funei New Jersey garden 7,202,000 711,000 313.000 New Jersey orchard 8,257.000 611,000 375.000 New Jersey meadow 10,133,000 900,000 925.000 New Jersey forest 2,088,000 1^20,000 318,000 New Jersey muck 2,600,000 150,000 M^'lltown bogs 185,000 33.000 Buckalew bogs 450,000 12,000 43.000 Iowa soils 220,000 281,000 113,000 T/>iiisiaTia soil . . , 10,000,000 2,000,000 119,000 ra1ifnrTir> fprti1i»,P<1 3,840,000 680,000 108,000 California unfertilized 6,444,000 356.000 36,000 Oregon muck 7,900,000 1,400,000 400,000 Orpgrm white lf>T"1 3,400,000 300,000 300,000 Porto Rico soil 2,140,000 960,000 300,000 North Dakota wheat 2,070,000 933.000 30,000 North Dakota flax 1,730,000 263,000 23,000 Hawaiian soil 4.335,000 665,000 76,000 6,035,000 566,000 330,000 2,125,000 574,000 30,000 Colorado soil 2,440,000 1,560,000 230,000 Maine Aroostook loam 4,650,000 250,000 85,000 Maine Aroostook infested 15,000,000 2,200,000 300,000 Canada soil 1,600,000 1,100,000 112,000 12 Diseases of Greenhouse Crops a. fonn which plants can use. They must at first be acted upon by certain definite micro-organisms in the soil. A. The Transformation of Carbon. Cel- lulose, which is but a form of carbon, consti- tutes a large per cent of the woody tissue of plants. Soils contain large amounts of cellulose ^id this un- doubtedly helps to maintain their proper physical condition. It is found in large quantities in straw, manure, or in green vegetable matter. But because of its ccHnplex form, plants cannot make use of it, until it imdergoes a certain decomposition. This is accomplished by a group of soil bacteria known as Amylobacter, which, feeding on the dead vegetable cellulose, break it up, and reduce it to carbon dioxide, hydrogen and fatty acids. The carbon dioxide either returns to the air to replenish the atmospheric supply, or it unites with water to form carbonic acid and soil carbonates. The carbon dioxide is taken by the plants either directly from the air through the leaves, or from the soil in some carbonate form. Thus we see that it is not the cellulose nor the prod- uct of its decomposition that furnishes plant food, but certain inorganic elements which are set free in its decomposition. B. Elaboration of Available Nitrogen. From the viewpoint of plant nutrition, nitrogen is unquestionably the most important of all elements.; The nitrogen of the air, although totaling about 79 per cent of it, is not in an available form. In the transformation of proteids into available nitrogen in The Healthy Soil 13 the soil, three definite processes take place, all thanks to the work of certain soil micro-organisms. 1. Ammonification. In this process, the soil bac- teria attack the complex proteids and convert them into ammonia. The odor of ammonia from decom- posed urea, manure, or any other organic matter is always an indication that ammonification takes place. According to Sackett * and others the ability to bring about this change is attributed to the follow- ing soil bacteria: Bacillus mycoides. Bacillus pro- tens vulgaris. Bacillus mesentericus vulgatus. Bacil- lus subtilis. Bacillus janthinus. Bacillus coli commu- nis. Bacillus megatherium. Bacillus fiuorescens lique- faciens. Bacillus fiuorescens putidus and Sarcina lutea. Recent investigations by Waksman f and others indicate that certain classes of fungi are even stronger ammonifiers than are bacteria. Trichoderma Koningi and the Mucorales fungi were found to be strong ammonifiers. Fun^, too, are very strong cellulose decwnposers. Further extensive investiga- tions on soil fungi will no doubt more strongly es- tablish their relationship to ammonification. 2. Nitrification. In order to be readily available for plants, ammonia and ammonia compounds must be changed still further into simpler compounds or, as the process is known, must imdergo nitrification. The ammonia is first oxidized into nitrous acid and nitrates. This is accomplished by soil bacteria, Ni- •Sacket^ W. G, Colorado Agr. Expt. Sta. Bui. 196: 3-39, 1916. t Waksman, A., Soil Science 2: 103-155, i9»6- 14 Diseases of Greenhouse Crops trosomonas and Nitrosocoscus. The nitrates are then oxidized into nitric acid and nitrates, through the work of the bacterium, Nitrobacter. The nitrates are the only forms of nitrogen which plants can use. C, Action of Soil Flora on Mineral Sub- stances. Inert mineral substances, like the organic matter in the soil, must first be acted upon by cer- tain soil bacteria to be converted to a form which plants can readily assimilate. 1. Changes of Phosphates. Phosphates as they commonly occur in nature are but little soluble in water. This is why they cannot be used in their first form, although they are required by most plants. Soils deficient in this element may be im- proved by such fertilizers as superphosphate of lime, groimd bone, phosphate rock or Thomas slag. In the process of decomposition of organic matter a large quantity of carbon dioxide is liberated, which unites with die water in the soil to form carbonic acid. This acid attacks the insoluble phosphates, transforms them into superphosphates — ^the only form soluble in water, — and renders them available to plant life. 2. Changes in Potassium, Sulphur, and Iron. The carbon dioxide and other organic acids pro- duced during the fermentation of organic mat- ter, attack the potash feldspar which occurs in the soil. The product is potassium carbonate which is soluble in water and hence readily taken up by plants. The nitric acid which is formed dur- ing nitrification may also combine with the raw pot- The Healthy Soil 15 ash in the soil, fonning potassium nitrate which is a form available for plants. As a result of the activity of soil bacteria, hydro- gen sulphate is evolved from the decomposition of proteids. The sulphur may be further changed into sulphur dioxide, and when combining with water and oxygen, into free sulphuric acid. The latter readily combines with calcium or magnesium, form- ing calcium or magnesium sulphate, from which the plant obtains sulphur for the construction of its proteids. CHAPTER 2 SICK SOILS When a soil is sick, either because its beneficial bacteria do not perform their functions properly, or because of abnormalities in its chemical or physical properties, careful treatment and proper cultural methods may restore it to health. But when a soil becomes sick and unproductive because parasitic forms gain a foothold in it, much greater skill and knowledge are required to cope with the problem. Its solution is of the greatest economic importance to the gardener and to the greenhouse man. Parasitic fungi, upon finding their way into a soil, do not necessarily interfere with the work of the beneficial bacteria, such as the ammonifiers and ni- trifiers, for instance. Nor do they always influence the chemical or physical nature of the soil. Many of them directly attack the crop itself, causing serious diseases in the plants. Damping Off This disease is "very familiar to every grower of plants. It is peculiar to seedlings or tender plants, and is very prevalent in the greenhouse, the hot bed, i6 Sick Soils 17 the cold frame as well as in the field. It is induced by the presence of definite parasitic fungi, which thrive best in overwatered soils, and when the green- house is kept at a comparatively high temperature with poor ventilation. Damping off is also favored by thick sowing and too much shade in the seed bed. Symptoms of Damping Off. Every experienced grower knows the disease when he sees it. Seed- lings freshly damped off are soft and water soaked at the base of the stem. If they are pulled they often break off easily. A more careful examination shows that the root system is entirely decayed, al- though the upper part of the stem and leaves may still be green, and also possibly fresh. The degree of prostration in the seedlings is determined by the amount of moisture in the soil. If it is slight, the seedlings will become flabby and wilted before they topple over. With a high moisture content, they are more firm, but become prostrate as soon as in- fection sets in. The trouble usually begins in spots in the bed, thence spreading in every direction. Damping off is usually caused by several fungi, the chief of which is Pythium de Baryanum Hesse. The organism was first named and described by Hesse in 1874. Ward * found it to be a very prevalent para- site in the garden soils of Europe. In America the fungus was first recognized as of great economic im- portance by Atkinson.t The seedlings of most •Ward, M., Quart. Jour. Micros. Soc. New Ser. 22: 487, iXij. t Atkinson, G. F., New York (Cornell) Agr. Expt. Sta. Bui. 94: 233-272. i«9S- ^-a U nl 5.2 Is i2 ■■£• •-g rt o •B o^ S w 'J — .S'm :is Sick Soils 19 The latest investigations have not yet disclosed whether or not Pythium de Baryanum is carried over from year to year by its oospores. It is apparently able to propagate itself indefinitely by its vegetative mycelium. Of the other fungi which are capable of pro- ducing a damping off in the greenhouse or seed bed may be mentioned Sclerotinia Uhertiana Fckl., Phoma solani Hoist., Colletotrichum sp., Fusarium sp., Sclerotium rolfsii Sacc. and Rhizoctonia solani Kuhn. Each of these, except the last, will be taken up separately in connection with the study of their respective hosts. The fungi which cause damping oif are introduced into the greenhouse, primarily v/ith sick soil used in the compost, and also with infected manure. The practice of dumping diseased plants and all other infected material in the manure pile cannot be too strongly condemned. Sometimes very lightly infect- ed plants with no visible symptoms of disease in the seed bed may nevertheless act as carriers, and like- wise infect the greenhouse soil. Damping Off of Cuttings Greenhouse men are often troubled with a damp- ing off of cuttings. In specific cases this is brought about by parasitic fungi which, however, will be taken up at length under the discussion of the va- rious hosts. 20 Diseases of Greenhouse Crops Root Rot Caused by Rhizoctonia solani Kuhn. Although not so virulent as Pythium, Rhizoctonia is a frequent cause of considerable failure in green- house culture. The fungus causes a damping off of seedlings and cuttings and a serious root rot. Symptoms. The symptoms of Rhizoctonia rot or wilt do not differ materially from those produced by Pythium de Baryanum. On older plants, however, Rhizoctonia produces cankers or deep lesions which are very characteristic. These are formed on the roots as well as on the base of the stem. The lesions are reddish brown and extend into the cortical or vital layer as well as into the woody tissue. There is perhaps no other parasitic fungus which is so widespread and which is capable of attacking such a variety of hosts as Rhizoctonia. The work of Peltier * shows that the following greenhouse crops are susceptible to Rhizoctonia: beet, bean, cauli- flower, celery, cucumber, egg plant, horseradish, lettuce, muskmelon, pepper, radish, tomato, sweet alyssum, amaranthus, omamencal asparagus, china aster, begonia, candytuft, carnation, coleus, dianthus, lavatera, lobelia, pansy, poinsettia, sweet pea, violet. Cuttings of the following hosts are also reported by Peltier to damp off from Rhizoctonia : Abutilon hybridum, var. lavitzii, Acalypha wilkesiana, var. •Peltier, G. L., Illinois Agr. Expt. Sta., Bui. 189: 283-391, 1916. Sick Soils 21 bicolor, A. wilkesiana, var. tricolor; A. wilkesiana, var. marginata, Ageratum mexicanum, Alyssum odor- atum; Coleus, Cuphea phatycentra, Tresine, Petu- nia, Piguerua trinervia, Lautolina chamoecyparissus, Sedum spectabile, Althernanthera, Vincia major. The Organism. In the United States the first ex- tended account of Rhizoctonia was given by Pam- mel.* Many other excellent accounts by American workers have appeared from time to time, to which we shall have occasion to refer later. The genus Rhizoctonia includes several forms of sterile fungi, all of which are distinguished by the manner of growth in pure culture, and by its myce- lium. Young hyphse of R. solani Kuhn are at first hyaline, then deepening in color from a yellowish to a deep brown. The young branches are somewhat narrowed at their point of union with the parent hyphse and grow in a direction almost parallel with each other. A septum is also laid down at a short distance from the point of union with the parent mycelium (fig. 3, d and e.). There is another form of hypha which is made up of barrel shaped cells (fig. 3, f.), each of which is capable of germinating like a spore. In pure cultures R. solani produces sclerotia which are first soft, whitish, and which later become hard and dark. The fungus is, carried over from year to year as sclerotia which are able to withstand the effects of heat, cold, drought, or moisture. *Panimel, L. H., Iowa Agr. Expt. Sta., Bui. 15: 244-251, 1S91. 22 Diseases of Greenhouse Crops Parasitic Soil Fusaria Next in importance to Rhizoctonia is a group of fungi which belong to the genus Fusarium. Soils infected with these species of fungi become unfit for tomatoes, sweet peas, etc., thereby causing great financial losses to the greenhouse man. Individual difficulties will be taken up in studying each of these crops separately. As an illustration of a typical Fusarium sick soil let us consider the wilt of sweet pea. The cause of this trouble is a soil inhabiting fungus, Fusarium lathyri Taub. Symptoms. The first symptom of the disease is a sudden flagging of the leaves, accompanied by gen- eral wilting and collapse of the seedling. Usually upon sowing the seeds a fair percentage germinate and reach the height of about 8 to lo inches before they are attacked by the fungus (fig. 7, b.). If the collapsed seedlings are allowed to remain on the ground, the stems will soon be covered with the sickle shaped spores. Eventually the decayed tis- sue rots and is soon invaded by small fruit flies which now begin to distribute the fungus from place to place by carrying its spores. The Organism. The mycelium of Fusarium lathyri is hyaline, septate and branched. At an early age the mycelial cells round up into countless num- bers of chlamydospores. Old cultures are practically one mass of these resting bodies. The spores are of two sorts, the macroconidia which are sickle shaped, Sick Soils 23 3-4 septate, the microconidia are one celled, minute spherical to elliptical. Soils Rendered Sick by Certain Forms of Animal Life. Some soils are made sick by the presence of minute forms of animal life. A striking instance of this is the root knot, a disease produced by a little worm generally known as nematode, or eel worm. Root Knot Caused by Heterodera radicicola (Greef) Mull. Although root knot is most prevalent in light soils, it may sometimes be found in heavier lands. The trouble is most widespread out of doors in the South- ern States, where the winter is mild. In the North the worm is usually unable to winter over in the open unless it is protected by trash or dead weeds. It is, however, prevalent in greenhouses and is un- doubtedly introduced with sick soil brought in from the field. Symptoms. The disease is characterized by swell- ings or knots on the roots. These swellings may be variously shaped, and are often mistaken for the true nodules of legumes (fig. 22.). Infected plants become stunted, pale, and usually linger for a long time before dying. The Organism. The nematode is a very minute worm, seldom exceeding one twenty-fifth of an inch in length. It is semi-transparent so that it cannot be easily detected by the naked eye. In searching for the eel worm, it is necessary to break a fresh knot 24 Diseases of Greenhouse Crops (fig. 4, a-e.). Close examination will reveal two types of worms; a spindle shaped worm, the male, and a pearly white pear shaped organism, the fe- male, firmly embedded in the gall tissue. The fe- male is very prolific, depositing no less than 400 to 500 eggs during her lifetime. The eggs are whitish, semi-transparent, bean shaped bodies, and too small to be noticed without the aid of a magnifying glass (fig. 4, f.). The time which elapses until the eggs hatch (fig. 4, f-u) depends largely upon weather conditions. In warm days the eggs hatch sooner than in cold days. Upon hatching, the young larvae either remain in the tissue of the host plant in which they emerge, or, as is more often the case, leave the host and enter the soil. This is the only period during which the worms move about to any great extent in the soil, where they either remain for some length of time or immediately penetrate an- other root of the host. The nematodes in most cases become completely buried in the root tissue, estab- lishing themselves in the soft cellular structure which is rich in food. The head of the worm is provided with a boring apparatus consisting of a sharply pointed spear, located in the mouth. This struc- ture not only aids it in getting food but is also val- uable in helping the young worms to batter through the cell walls before becoming definitely located. The two sexes during the development are indis- tinguishable up to fifteen or twenty days, both be- ing spindle shaped. In the molting or shedding of the skin, there is a marked change in the case of the Fig. 4. Nematode. a. Very young, normal root, h. mature, normal root, d, young root same age, c. attacked by nematodes, d. same, one week later, e. section of mature gall, showing distortion of tissue, f-u. the various stages of development of the young embryo worm, beginning with /, as the egg and ending with u as the mature worm ready to hatch (o-« after G. E. Stone and R. E. Smith). Sick Soils 25 female, especially in the posterior region of the body, which no longer possesses a tail-like appen- dage. Fertilization occurs soon after this molt, and many radical changes occur in the shape and struc- ture of the organization of the worm. The fer- tilized female increases rapidly in breadth and be- comes a pearly white flask or pear-shaped individual. At this stage it is far from being worm-like and may, therefore, be overlooked by one unfamiliar with the life-history of the eel worm. The young male is much like that of the young female larvae, being spindle shaped in outline. The male does not cause as much damage to the root tissue as the female, and its purpose in life seems to be only that of fer- tilizing the female, for after this function has been performed, it is quite probable that the male worm takes no more food. Omnivorous Nature of the Eel Worm. There are two hundred I thirty-five species of plants known to suffer fron le eel worm. This number includes all the important families of the flowering plants. According to Bessey * the following are among the greenhouse plants subject to root knot: bean, beet, cantaloupe, cauliflower, cucumber, egg-plant, lettuce, radish, tomato. For methods of control, see p. 40. Leaf Blight Nematode Caused by Aphelenchus olesistus Rizema-Bos. Beside the root knot disease which is caused by •Bessey, E. A., U. S. Dept. Agr. Bureau PI. Ind. Bui., 217: 7-8^ 1911. 26 Diseases of Greenhouse Crops Heterodera radicicola there is another nematode which confines its injury to foliage only. Of the greenhouse hosts affected by this pest may be mentioned the Begonia, Asplenium nidus-avis, Pteris serrulata avistata, Pteris wimeseth, Pteris tremula, and Pelargonium. Sym-ptoms. On the Cincinnati begonia the symp- toms, according to Clinton,* are manifested as nu- merous small indistinct discolorations limited by the small veinlets. In time, however, the tiny spots en- large and unite, forming a conspicuous reddish-brown blotch. Frequently infection is manifested as long streaks along the main veins. Often isolated spots occur in the midst of the surroimding healthy tissue (fig. 5, a.). On Asplenium nidus-avis, the trouble becomes conspicuous in dark brown areas from the base of the leaf near the midrib. These spread ujv ward until the entire lower half of the leaf is killed. On Pteris, the spots appear as reddish brown bands reaching out from the midrib to the border, but lim- ited sidewise by the small parallel cross veins (fig. 5, b.). The Organism. The nematode in question is a slender microscopical worm. The latter chooses the air chamber of the leaf in which to lay its eggs and upon hatching travels around in different parts of the same leaf or to the neighboring foliage. The worm can travel only when there is a wet film on the leaves. •Clinton, G. P., Connecticut Agr. Expt Sta, Thirty-ninth Ann. Rept.: 455-462, 1916. Fig. 5. Leaf Blight Nematode. n. Infected begonia foliage, b. the blight on fern leaves (a-b, after Clinton). Sick Soils 27 Control. Immersing fern plants for five minutes in water heated to 122 degrees F. (50 degrees C.) does not seem to injure the ferns, but seems to kill the nematode. All infected leaves should be cut off and burned. Diseased plants should be isolated f rwn healthy ones. Spraying with Bordeaux may also act as a repellant. CHAPTER 3 TREATMENT OF SICK SOILS Our conception of a healthy soil as has been in- dicated is one which is ideally suited to plant growth, through proper physical and chemical make-up, and by the presence of groups of beneficial micro-organ- isms. A sick soil is one in which plants would grow very languidly or not at all. Soil sickness may be caused through the improper use of fertilizers, or through the introduction of parasitic disease-produc- ing organisms. Acid-Sick Soils Soils which contain an excess of acid, in which crops refuse to grow, may be termed acid-sick. Acids in soils have a directly poisonous eflFect on plants. Soil acidity may be brought about by the loss of lime and of other bases; and by the decomposition of organic and of inorganic matter. Crops are known to draw heavily on the lime of the soil, and thus to increase the proportion of acidity. This, then, is one direct way of depleting the soil lime. Lime and other bases are further lost from the soil by leaching. The soluble car- bonates are but slowly soluble in pure water. How- ever, carbon dioxide, nearly always present in soils, 28 Treatment of Sick Soils 29 changes the calcium carbonate into calcium bicar- bonate, which is very soluble, and readily leaches out with the drainage water. Soils which are heavily manured are apt to be- come more acid. The decomposition of the organic matter yields large quantities of carbon dioxide which act on the carbonate in the manner above in- dicated. In addition to these causes, poor drain- age has a tendency to increase the soil acidity. The application of ammonium sulphate as a fertilizer leads to a development of acidity by the production of sulphuric acid. The same is true when other acid fertilizers are used. In the process of nitrifi- cation, in which nitrogen is made more available for plants, acids are produced. Acidity in a soil is usually characterized by a languid condition of the growing crop. This may be due directly to the effect of the acid on the plants, or to the inhibiting effect of the acid on the soil flora. In the latter case the plant food in the soil, although very plentiful, may not be in a form available for plants. Not all crops are equally sensitive to soil acidity. Hartwell and Damon* have determined the degree in which truck crops are benefited by the application of lime to an acid soil. Those which are very sen- sitive to soil acidity are followed by the number (3), while a lesser degree of sensitiveness is indi- cated by the numbers (2) and (1). Crops which tolerate a moderate amoimt of acidity are followed *HartweII, B. L., and Damon, S. C, Rhode Island Agr. Ezpt Sta. Bui. 160: 408-446, 1 9 14. 30 Diseases of Greenhouse Crops by the figure (o), and those which thrive best in acid soils ( — i); beans (o), beets (3), carrots (1), cauliflower (2), celery (3), cucumber (1), egg- plant (2), lettuce (3), muskmelon (o), parsley (o), pea, garden (1), pepper (3), radish (1), rhubarb (3), sorrel (—1), spinach (3). Treatment of Acid Soils The best known remedy for soil acidity is lime. Its effect is to neutralize the acidity, and to restore the normal equilibrium for the activity of the soil flora, thus overcoming the antagonism to normal growth. The amount of lime to be used depends on the kind of soil, its degree of acidity, and the crops grown. It is very unlikely that injury would result to greenhouse crops from the use of moderate amounts of lime. Lime is sold as ground limestone or as burned lime. A ton of burned limestone will yield 1,120 pounds. If enough water is added, it will weigh 1,480 pounds. If 1,120 pounds of burned lime or the 1,480 pounds of hydrated lime are allowed to air slack, the weight of both will be 2,000 pounds. Air slacked lime has the same com- position as ground limestone. In buying hydrated lime we do not get any better quality, but merely pay an excess in freight for the amount of water it contains. The cost of delivery should determine the kind of lime to buy. Wood ashes may often be used instead of lime to correct soil acidity. Hardwood ashes contain about 30 per cent, lime and 60 per cent, potash. Treatment of Sick Soils 31 Two and a half tons of good wood ashes are equiva- lent to one ton of burned lime for overcoming soil acidity. Leached ashes have lost their potash and its lime is in the form of a hydrate or carbonate. Magnesium lime, which contains a high percent- age of magnesia, is not objectionable for use. In fact, a ton of limestone, which contains magnesium carbonate is more effective on acid soil than a ton of limestone without magnesium carbonate. Lime should be applied only when the acidity of the soil requires it. Alkali Soils Alkali soils are termed sick, since plants thrive there poorly or not at all. The alkali problem gen- erally concerns only those greenhouse men located in the irrigated districts of the arid or semi-arid regions of the United States. For convenience, alkali soils are here divided into black and white. The black alkali lands are known to contain sodium carbonate or washing soda as the essential salt. The latter does not act so much on the soil as on the organic matter, turning it black. This dark material is always found on the surface with the salts. The blackening of the soil, however, is not always an indication of black alkali. Many dark spots are found to contain the white alkali. Moreover, soils which contain little or no organic matter may contain large quantities of sodium car- bonate and never turn black. The white alkali in reality is not a true alkali. The salts found in it 32 Diseases of Greenhouse Crops are sodium chloride or table salt, calcium sulphate or gypsum, sodium sulphate, magnesium sulphate or epsom salt. In addition to these may be found salts of potassium. Methods of Control. Generally speaking the al- kali problem is not serious in greenhouse culture. The alkali soil when mixed at the compost heap generally loses much of its salts due to the action of the manure used. However, in alkali regions alkali soils should be avoided as much as possible. When this is not possible the soil to be used with the compost should be spread out and exposed to the action of winter weather conditions and to the washing by rain. This treatment will result in a loss of the injurious salts through leaching. Soil Sterilization Damping off, whether induced by Pythium, Rhi- zoctonia or any other parasitic organism, is usually confined to seedlings in the seed bed under cover or in the open. The loss of seedling not only means a waste of seeds, but it also results in poor stands. The disease-producing-organisms are usually brought in with the manure and the compost. Most growers are in the habit of using the same soil in the seed bed or in the greenhouse year in and year out. A number make it a practice to empty their beds and use fresh soil every year. This, however, is too expensive and, moreover, is not always a safe method, for the new soil, too, may be contaminated, or may become infected as soon as it is placed in the Treatment of Sick Soils 33 bed previously contaminated. Fortunately, sick soils in the greenhouse, unlike the soil outdoors, may be readily treated so as to destroy all forms of para- sitic micro-organisms or injurious animal life which are present in it. The various methods to be men- tioned make it possible to use the soil over and again. Rid the soil of parasites, then all chances will be in favor of good crops whether vegetables or flowers. Soil Treatment with Formaldehyde When steam sterilization is not feasible, because of the absence of suitable steam pressure, the for- maldehyde treatment is the next best. With this method we may control Fusarium, Rhizoctonia, and P^thium in infected beds. It is doubtful, however, if it will entirely eradicate eel worms from infested soils. The method is as follows: the beds are thor- oughly prepared in the usual way with all fertilizers worked in and then the soil is drenched with a solu- tion of formaldehyde composed of one pint of the chemical (40 per cent, pure) to 30 gallons of water applied at the rate of one gallon per square foot. The solution should be put on with a watering can and distributed as evenly as possible over the bed, so as to wet the soil thoroughly to a depth of one foot. It will, in most cases, be necessary to apply the solution in two or three intervals, as the soil may not absorb the full quantity of the liquid at one time. After treatment the beds should be cov- 34 Diseases of Greenhouse Crops ered with heavy burlap to retain the fonnaldehyde fumes for a day or two, and then aired for a week before planting. Stirring the soil at frequent inter- vals after uncovering hastens the more rapid escape of the formaldehyde fumes. Sterilizing Soils with Steam Steam sterilization of soils is by far the best method. There are four waj^ of steaming soils: (l) Inverted pan method, (2) the perforated pipe system, (3) the steam rake device, (4) the drain tile method. The choice of any one of these methods is a matter of expediency. All four methods have been successfully used on a commercial scale. The Inverted Pan Method. This was first devised by A. D. Shamcl of the U. S, Department of Agri- culture. To carry it out, the boiler must maintain 9. pressure of not less than 80 pounds, for at least one and a half hours. In setting a pan, the rim is simk into the soil of the seed bed or bench, to a depth of two to three inches, to make the inclosed chamber steam tight. In heavy soil, trenching may be necessary. It is also advisable to put a heavy weight on the pan when the steam operates. For one pan, a traction engine or a portable boiler of ten to twelve H. P. will suffice. While the standard of the pan is six by eight feet, the dimensions may be modified to suit the seed beds or greenhouse benches. Treatment of Sick Soils 35 Selby and Humbert* describe the method of con- structing an inverted pan as follows : "Material used for construction of a pan is gal- vanized sheet iron; the most useful weight is No. 20 gauge, which weighs 26.5 ounces per square foot. The heavier material requires little in the way of frame supports. The galvanized iron sheets come in sizes varying from two to three feet in width by eight to ten feet in length. The standard is a pan 6x10 feet in area, six inches deep, constructed from 5 such strips 2j^ x 8 feet in size. These sheets are joined by double fold seam and riveted at inter- vals of 6 to 10 inches to make the pan steam tight. This pan is further strengthened by a band of strap iron 2x1 inch riveted to the bottom edge, and stiffened by a brace of ij4"iich angle iron across the top and extending down the sides. This is bolted at the sides to the supporting strap iron stiffener. "The entrance pipe for the steam may be placed at the side or end of the pan or may enter from the top. The latter forai has the advantage in that it will not interfere with the box boards when used on frames. The pipe, after entrance, should be a T form, so that steam in being forced into the pan when in place does not blow holes in the soil." The pans, together with the sand bags used for weight, are mounted on a frame which rests upon wheels. The wheels run on the edges of the con- •Selby, A. D., and Humbert, J. G, Ohio Agr. Eipt Sta. Circ. 151: 65-74. 1915- 36 Diseases of Greenhouse Crops Crete walks on either side of the house. By using a pulley, the pan may be conveniently placed wherever desired. Perforated Pipe Method. The apparatus consists of a set of perforated pipes buried in the soil and connected with a steam boiler. The main and cross- head pipes are 2 inches and those which are buried lyi inches. The length of the beds, and especially the capacity of the boiler, will determine the num- ber of pipes to use. However, 7 to 8 pipes are as many as could be used to advantage. These should not be over 40 feet long. The perforations should be one-eighth to three-sixteenths of an inch in size, 12 to 15 inches apart and on the upper side of the pipes. The latter are buried about six inches deep and when the steam is turned on the beds are cov- ered with a heavy canvas to retain the heat and to prevent the escape of steam (fig. 6, a and b.). When- ever convenient, it is well to have two sets of pipes so as to save time and fuel. Steam Rake Method. This consists of a two-inch main pipe which may be run between two sets of houses. The pipe is connected with the boiler at one end and with a heavy hose at the other. The rake is attached to the hose through which the steam is introduced. There are either two rakes used in a single house, or four rakes operated in pairs, end to end in two adjoining houses. The rake is gener- ally composed of three main pipes 13 feet long, which run crossways of the house, and of several cross pieces one inch in diameter that are gradually Fig. 6. a. Steam sterilization apparatus, b. bed ready to be ster- ilized, showing steam connection and burlap covering. Treatment of Sick Soils 37 reduced to three-fourths inch, then to one-half inch, then to three-eighths inch. The pegs are six inches long, and are placed eight inches apart, and consist of (Mie-fourth inch pipe poiuided together at the lower end. The steam escapes through a three- sixteenths inch hole at the lower wedge-like end of the pipe. The advantage of this apparatus is that it can be made to fit any bed. At 90 to 100 pounds pressure, more steam will naturally pass through the pipes than at thirty to forty pounds pressure. During the operation, a canvas cover laid on the beds will prevent the rapid escap>e of steam. The Tile Method. This system is at its best when the steam pressure is low, at 25 to 30 poimds. With higher pressures the steam will blow out between the tiles. With this method, therefore, the soil should be sterilized for a longer period of time, from two to four hours, depending on the depth of tile and oa soil conditions. Usually the tiles are not l^d over one foot deep and from two to three feet apart. The joints of the pipes should be well matched. Hot Water Sterilization. Numerous greenhouse men seem to prefer the use of hot water as a soil sterilizer to any other method here mentioned. Mr. Wm. L. Doran of the Massachusetts Experiment Station, who has made oMisiderable study of this method, writes as follows: "The soil should be thoroughly dry in the begin- ning so that it will take up the maximum amount of water. Before treatment, it is spaded over to 38 Diseases of Greenhouse Crops a depth of one foot to insure an open, porous con- dition. The water is heated in an ordinary boiler such as is used for heating the greenhouse, no extra equipment being needed. It is moved by a small pump operated by a motor and gasoline engine of a small horse power. The water comes out under forty pounds pressure, which insures considerable penetration into the soil. It is piped from the boiler through the center of the greenhouse in ij^-inch iron pipes. Most growers take the water from the bottom of the boiler rather than from the top, the object being to keep the temperature high but to avoid the steam which is objectionable. A ther- mometer is screwed into the main outlet pipe and is read frequently; the temperature should be above 201 degrees F., but if it goes much above 215 de- grees F. the outlet pipe spits steam and is difficult and dangerous to use. To this iron pipe in the cen- ter of the house is attached a one-inch rubber hose fifty feet in length. This hose is replaced annually to decrease the danger of blow-outs and bums. Most growers sterilize once a year, some twice. The rubber hose is attached at the other end to a Y joint which is in the middle of a five-foot iron pipe one inch in diameter. The upper half of this pipe is plumed at both ends, serving simply as a handle, and from the lower half the water is delivered to the soil. A few feet back of this exhaust pipe the rubber hose is wrapped with burlap so that it may be carried over the shoulder of the workman. Some Fig. 7. Effect of Soil Sterilization. a. To left, sterilized soil planted in sweet peas, to right Rhizoctonia sick soil unstertlized and where seed failed to germinate. b. To left, sterilized soil planted in sweet peas, to right, Fusarium sick soil unsterilized, where seed failed to germinate. Treatment of Sick Soils 39 growers shove the iron pipe down into the soil six inches; others hold it above the surface of the soil. The water penetrates equally well either way, be- cause the soil is in a loose condition and the water goes out under pressure. There are no figures as to the exact amount of water per cubic foot of bed sur- face, but hot water is applied until it stands on the surface of the soil in pools and will no longer pene- trate. The exact amount will, of course, vary with the physical ccmdition of the soil and its relative dryness. The greenhouse men do not practice cover- ing the soil with anything to hold in the heat. Out of doors, however, a cover would be desirable because of wind currents. Three or four days after treatment, the soil is cool enough and dry enough to plant." It will require about two days for five men to treat a house 275 feet by 34 feet. Roasting or Fan Firing. By this method, the soil to be sterilized is removed ixoai the bed and placed in a pan, over a hot fire. After roasting, the soil is returned to the bed and more of it steril- ized. This method is too slow and has the disad- vantage, besides, of destroying the humus in the soil. The advantage of steam sterilization and of the "fire" methods lies in the destruction of all weed seed, together with the fimgi which cause damping-ofiE (fig. 7, a and b.). 40 Diseases of Greenhouse Crops A New Method of Steam Sterilization for Controlling Nematodes* It has been our common experience, when at- tempting to control nematodes by steam steriliza- tion of the soil, that very frequently one is tmable to secure sufficient steam pressure satisfactorily to use the common harrow-type of sterilizer, the in- verted pan or any modification of these types. When the steam pressure is only 50 to 60 pounds or less at the boiler, and where it becomes necessary to carry this a considerable distance in the green- house, condensation takes place, and as a result these sterilizers cause puddling of the soil and other- wise inefficient work. In our experiments, all modi- fied types of steam sterilizers which originated from those already mentioned were equally unsatisfac- tory; therefore, a method which could utilize a low steam pressure and still do good work without in- jury to the soil, seemed urgent. The method to be described herewith was used in a span of fifteen greenhouses, which had the soil badly infected with nematodes. For two successive seasons previous to the treatment of the soil, the entire crops of tomatoes and cucumbers were a total loss. After unsuccessfully trying out all styles of steam sterilizers, the device herein described was de- vised and proved successful. It should be remembered where 80 pounds or •By L. E. Melchers, Kansas State Agricultural Experiment Station. Treatment of Sick Soils 41 more pressure is obtainable, the aforementioned kinds of apparatus may give very good results, but where the pressure is less, as in many cases in steam heated plants, they are not satisfactory. The necessary equipment for this new device con- sists of two 2 X 4's cut at suitable lengths, a few boards either the entire length or half the length of the width of the greenhouse, canvas, burlap, sacking or tarpaulin. This method has been devised purposely for greenhouses growing vegetables on the ground, although modifications of this method could be made to suit other conditions. The first operation in carrying out the work con- sists of digging a pit at one extremity of the house to the depth that one wishes the soil sterilized. The width and length depend somewhat upon the width of the greenhouse. In our work the pits were dug 12 inches deep, 6 to 8 feet wide and 10 to i^ feet long. Two 2x4's are laid on edge in the bottom of the pit. These pieces should be the length of the pit and placed about 6 to 12 inches from the sides of the pit. One or two leads of steam pipes with T out- lets in the center and at the ends of the pipes should be laid in between these two stringers (2 x 4's) . The pipes can best be run in from the ends of the pits. It has been found better to let the steam out in large quantities and not through perforated pipes. Pieces of 2 X 4's are then laid across these two stringers and should be long enough to reach across the width of the pit. Quite a large nrmber are necessary to form a kind of platform. About a quarter of an inch 42 Diseases of Greenhouse Crops should be left between the 2x4 cross pieces to allow for the ascent of the steam (fig. 8, a, b, c). When the bottom has been laid, the soil which was removed can be thrown onto the platform. Boards should be staked around the sides of the platform to retain the soil. This forms a kind of wagon box. The steam can then be turned on, ther- mometers placed in the soil and the entire pit cov- ered with any suitable covering to retain the heat. Since steam rises, this method is much more satis- factory than where it becomes necessary to force the steam downward. There is no puddling of soil, even at the lower pressures, and 212 degrees F. and higher temperature can be obtained when steriliz- ing 12 inches of soil. It should be remembered that a few inches of soil below the wooden platform is likewise sterilized in this process. The skeleton platform is easily removed by means of an iron bar with a hook at the end for catching hold of the 2 X 4's and jerking them from underneath the soil. When the framework has again been set and the steam pipes adjusted in place, the platform is ready for the second batch of soil, which is dug immedi- ately adjoining the soil which was just sterilized. In order to avoid extra labor, it becomes necessary to have one pit already dug just ahead of the bed being sterilized, so when the 2 x 4's are removed they can be laid immediately in the pit which is ready for them. This is accomplished by erecting the second bed on top of the first one, i.e., on top of the soil just sterilized. Fig. 8. Melcher's Soil Steriuzer. a. The 3x4 bottom laid and ready for the soil, h. bed ready for steaming, c. steaming the soil in two beds running the width of the greenhouse. Treatment of Sick Soils 43' When the second bed is ready for sterilization (// is directly on top of the one first sterilized), one has a pit already dug to set the framework in for the third batch, and frc«n hence on, a pit will always be in readiness for the framework. It will be seen by this process and by such procedure that it be- ccMnes necessary to return one batch of sterilized soil to the opposite end of the greenhouse, after the whole house has been sterilized. This is the second batch, which was sterilized and sets on top of the first. This cannot be avoided, but the soil can easily be carted back by means of wheelbarrows. Many greenhouses are irregularly constructed, with uprights and other obstructions more or less promiscuously scattered; therefore, the pan method is often difficult to use and it is less easy with the other unadjustable apparatus, but with the method just described these obstructirais are much less seri- ous, since they can be allowed to ccane in any part of the bed without hindrance to sterilization. There is a little more expense connected with this method, on account of extra labor which is neces- sary, but this method is not being advocated as a superior way of steaming the soil, but rather to do the work where situations arise that cannot be han- dled otherwise. Effect of Soil Sterilization on Seed Germination. The main object in sterilizing soils is to destroy the harmful fungus flora. Of all the methods here recommended, steaming is the most effective. Not all soils, however, are alike benefited by this treat- 44 Diseases of Greenhouse Crops ment. With lettuce seed, for instance, there is a higher per cent, of germination usually obtained in the sterilized soil. With tomatoes, however, ger- mination is retarded under similar soil treatment. On the average, germination is favored by soil ster- ilization. This is well shown in Table 2.* Table 2 Kind Total Number of Seed Tested Number Germinated in Per Cent. of Seed Stern- ixed SoU UnsterU- ited SoU Gain or Loss Radish 6oo 6oo 6oo 6oo 6oo 400 400 400 200 200 159 93 281 26 37 105 57 87 81 no 187 10 33 31 Ir 41 13 33 61 Tomato Cucumber Lettuce Tomato Onion |5 61 Mustard Turnip 64 43 70 Onion Effect of Soil Sterilization on Plants. That soil sterilization is practicable cannot be doubted. With some crops, the beneficial effect is especially marked. The Massachusetts Experiment Station t found a considerable increase in the production of violet blossoms as a result of soil sterilization. This is well shown in Table 3. •From the Massachusetts Agr. Expt. Sta., 15th Rept.: 40-42, 1903. t Massachusetts Agr. Expt. Sta., lath Ann. Rept.: 165-167, 1900. Treatment of Sick Soils 45 Table 3 Date No. of Blossoms Picked Unsterilieed Soa Sterilized Sou Percentage Gain \ November December. . . . January February March April Total.. Average 19 63 55 39 144 482 38 lOI 125 72 250 510 100 63 127 84 73 5 801 133 1,096 182 -36 Not only was production of flowers increased in the sterilized soil, but there was also a decided de- crease in leaf spots. Changes in the Soil due to Sterilization. Vari- ous investigators have found that by steam heat- ing, the physical, chemical, and physiological prop- erties of a soil are more or less changed. Through chemical action there is an increase of soluble mat- ter in some of the inorganic substances such as pot- ash and phosphoric acid as well as in the organic matter. Ammonia is also formed by the reduction of nitrates to nitrites and by the decomposition of organic compounds, large amounts of which are also made available for plant growth. This, then, would explain the reason of the stimulation of growth in sterilized soils. However, steamed soils may also contain injurious substances, which upon becoming soluble are harmful to plant growth and to the ger- mination of certain seed. This seems especially the 46 Diseases of Greenhouse Crops case in steamed soils deficient in lime. The inves- tigations of Schreiner and Lathrop* have shown that as a result of heating, dehydroxystearic acid is produced, and that this is harmful to plant growth. Heating soil produces both beneficial and harmful substances. The fertility is raised or lowered, de- pending on which of these predominates. The re- sult, however, is influenced by the crop, the fer- tilizer used, and the amount of lime applied. Cole- man t has found that intermittent sterilization by means of dry heat at 82 degrees C. for five suc- cessive days in moist soil produced but very slight chemical changes. But this slow method is not very popular with the grower. Since, however, sterilized soils lose their harmful substances by standing, the treatment of the soil during the summer months, when there is no crop in the greenhouse, will obvi- ate the main difficulty. Other Methods of Controlling 'Damping Of. Damping off may be largely controlled by careful cultural conditions. Unless the soil of the seed bed has been sterilized, it is unwise to use the same soil in the beds where damping off has occurred previously. Thick sowing, too, should be avoided. In Table 4, Johnson % presents some interesting data, showing the effect of thick sowing on damping off. •Schreiner, O., and Lathrop, E. C, U. S. Dept of Agr., Bur. of Soils, Bui. 89: 7-37, 1912. t Coleman, D. A., et at., Soil Science: 259-274, 1916. i Johnson, James, Wisconsin Agr. £xpt. Sta., Research Bui. 31: 31-61, 1914- Treatment of Sick Soils Table 4 47 Weight of Seed Sown Pl/iniK Plat Number Per Flat Per 100 Square Feet 1 Grams 0.1 0.2 0.3 0.4 0.5 0.6 0.9 1.0 Ounces 0.16 0.33 0.49 0.66 0.83 0.99 1. 16 1-33 Per Cent. 2 3 8 4 IS 35 75 80 g 7 8 80 g 92 96 10 Certain soils are especially favorable to damping off. Soils which contain a higher percentage of unrotted vegetable matter, and those which are hard to drain need special attention. Great care should be taken to keep the seed bed at the right tempera- ture. The latter cannot be guessed at by personal sensation. It should be accurately determined by thermometers placed in the bed at suitable distances. It should also be remembered that any covering cloth or sash will exclude light and air. Every precaution should, therefore, be taken to prevent the seedlings from becoming "drawn," for in that condition they are most susceptible to damping off. The safest plan is to keep the temperature a trifle lower than is generally required, and to allow as much ventilation as possible. Very often damping off starts only in one corner of the bed. To check the rapid spread of the disease, the infected area 48 Diseases of Greenhouse Crops may be removed. Spraying the seedlings with vari- ous fimgicides in a bed v^here damping off has be- come well established will be of little help. Control of Insect-Infested Soil. Spraying the soil will be of little value in the control of under- groimd insect pests. Fortunately, however, there are other means of dealing with them. All insect pests may, of course, be controlled by steaming the soil in the benches. Cut worms may be controlled by the use of a poisoned bran made as follows: To three ounces of molasses add one gallon of water and sufficient bran to make a fairly stiffened mixture. To this add a teaspoonful of Paris green or arsenic and stir well into a paste. A heaping teaspoonful of the mixture is scattered here and there over the infested bed. The cut worms will be attracted to the sweet- ened bran and after eating it will die from the poison. Summer Treatment of Greenhouse Soil The greenhouse is rarely used the whole year round. During the summer the house is usually idle one or two months. This is especially true re- garding truck crops, for at that time outdoor prod- ucts put the greenhouse out of cwnpetition. It is a common belief that if the soil is allowed to remain dry in the intense heat imdcr glass dur- ing July or August all injurious insects, fimgi and bacteria will be destroyed. To determine this point Treatment of Sick Soils 49 Green and Green* have carried out some interesting experiments. They used beds which had been treated as follows: New soil, straw mulch, manure mulch, and a summer soil, sun-dried soil, in the greenhouse. The results of these experiments with tranatoes are shown in Table 5. Table 5 Plot 1908 1909 1910 191 1 1912 1913 Average New soil 5-2 49 4-5 32 4-2 31 3-5 31 30 2.1 ... ... 3-3 2-5 2.6 •9 4-1 3-4 3-7 2.1 Straw mulch Manttre mulch Dry It is seen from Table 5 that as far as tranatoes are concerned the new soil gave the best results. The manure mulch is second in productiveness. The effect of the dry mulch shows a rapid decline, and the dried soil showed the poorest yield. It must be added that in this soil the greatest amount of disease was present. The result obtained with the soil treatment of tomatoes was found to be different frraa that with winter lettuce. This is more clearly brou^t out in Table 6 (see next page). This table shows that the drying of the soil does not affect the lettuce crop to the same extent as it does tMnatoes. Unlike most crops in the green- house, lettuce thrives best in old soil. On the other hand, cucumbers are as sensitive as the tomato to •Green, W. J, and Green, S. N, Ohio Agr. Expt. Sta., BuL s8i: 53-68, 1915. 50 Diseases of Greenhouse Crops Table 6 Plot 191 I 1911-12 1913 1912-13 Average New soil 3-74 329 432 3.01 4.61 5-25 iM 4.11 3-86 332 3.00 4.29 405 3-55 2.98 4.18 4. II Straw mtilch Manure mulch .... Diy old, well manured soil in the greenhouse. This does not imply, therefore, that it is necessary to renew the soil every year for cucumbers or toma- toes. Soil sterilization, good drainage, and liming will tend to overcome the ill effect of old soils on these crops. PART II CULTURAL CONSIDERATIONS CHAPTER 4 LIGHT IN ITS RELATION TO GREENHOUSE CULTURE Of the many factors which are intimately inter- woven with the growing of greenhouse crops, light is a very important one. Unfortunately, this sub- ject has received scant attention. However, Dr. Stone* of the Massachusetts Agricultural Experi- ment Station has contributed greatly to our knowl- edge on this subject. It is apparent from his work that success with greenhouse crops goes hand in hand with a thorough understanding of the light require- ments of plants. The problem of light has a direct bearing on the physiology and pathology of hot- house crops. Physiological Relationship of Light • To realize the importance of this subject we must be aware that nearly ninety-five per cent, of the substances contained in the plant is derived frcwn the atmosphere. These substances are manufactured through the action of light on the green matter (chlorophyll) located primarily in the leaves. This 'Stone, G. E., Massachusetts Agr. Expt Sta. Bui. 144: 3-39, 1913. 53 54 Diseases of Greenhouse Crops process is known as photosynthesis. It consists of an intake and assimilation of carbonic acid by the plant, and a simultaneous liberation of oxygen. The carbonic acid breaks down and combines with the water to form the sugars and starch. The spec- trum rays which are most concerned with the manu- facture of starch are the orange and the red. The blue rays aflFect growth. Success with greenhouse plants depends largely on the intensity and the na- ture of the light rays which are permitted to pene- trate through the glass. At best, these rays differ materially from the normal sunlight. Contrary to general belief, plants make most growth at night or in the dark. On the other hand, photosynthesis takes place during the daytime and under the direct influence of light. "While light does not favor growth, it assists in the development of supportive tissue which enables the plant to resist attacks of various diseases. The lack of a proper amount of light in the greenhouse causes the plants to possess little or no resistance to disease. This is especially true in the winter months. However, while insufBcient light is conducive to disease, an excess of it, such as occurs in the summer months, is also detrimental to plant health in the hothouse. In that case, shading the glass becomes necessary. Moreover, there are numerous hothouse plants, such as palms for instance, which naturally require less light. On the other hand, lettuce, tomatoes, cucum- bers, roses or carnations require more light in the Light in Greenhouse Culture 55 winter months than the ordinary hothouse is able to furnish. Pathological Relationship of Light While it is true that plants grow in the dark, they must have light to thrive. The growth made in darkness exclusively is of a soft nature. The long, whitish, slender sprouts of potato kept in the dark are a good illustration. Niimerous diseases of plants grown under glass may undoubtedly be traced to improper light conditions. Cucumbers, for instance, when grown in poorly lighted houses, becrane slen- der, producing elongated petioles and stunted leaves with little green color in them. Such plants, too, are soft, and possess little of the solid or resistant tissue. Poor light also makes cucumbers, as well as most other hothouse plants, susceptible to mil- dew, blight and leaf spots. Poor light and wet soils are responsible for the burning of the foliage of hothouse plants under fumigation. Too much light often affects the transpiration of plants and causes them to wilt unduly. Blosscan end rot of toma- toes vmder glass is more severe under bright light than under partial shading. No fixed rules can be given as to the light requirements of greenhouse crops. Until more definite knowledge is obtained on this important subject, the greenhouse manager will of course depend on his common sense, observa- tions and experience to guide him. 56 Diseases of Greenhouse Crops Construction and Management of Hothousbs AS Affected by Light Conditions From the previous discussion, it is now evident that to improve light conditions indoors will tend to produce normal growth and to hasten maturity. The greater the photosynthesis, the more rapid the assimilation of plant food, hence the quicker the growth. An increased amount of heat can never replace the normal effect of an increase of light for those crops which most require it. Many growers,- especially those who possess poorly constructed houses, often attempt to substitute heat for light in forcing. The result is generally a failure, because diseases of all sorts find the tender weak plants an easy prey to their attacks. The modem greenhouse man is partly solving the light problem by con- structing larger houses and using larger glass. As a result of this, more air space and more uniform moisture distribution is assured. The double-thick, third quality glass, used in previous years, is now being replaced by a good grade of double-thick, sec- ond quality glass. Improvements are also being introduced in the roof angles, for these, too, mean added and better light. The more closely the angle of the roof coincides with the right angle cast by the sun's rays, the greater the amount of light that may reach the indoor plants. In the old form of houses, many of which are still in existence, the glass used was from two to seven inches long and two to five inches wide, and was often lapped more Light in Greenhoujq Culture 57 than an inch. This system practically excluded fifty per cent, of the light. The modem house uses glass varying in dimensions from l6 inches by 24 inches, 20 inches by 30 inches to 24 inches by 24 inches. With the use of the larger glass, the diminished lapping results in a considerable saving of light. To prevent breakage of the larger glass a house must, of course, be solidly built and well purlined. The location of the house, too, influences the amount of light taken in. Houses located north and south are benefited by the morning light only, whereas those running west receive only the after- noon light. The ideal location from the light view- point would be to set the house on a line rurming 20 to 25 degrees north of east. Houses with greater roof angles naturally receive more light. It is also a well conceded fact that light will pass through a transparent object more easily if it is placed at right angles to the light rays. This fact is not often taken advantage of by greenhouse builders. However, it cannot be de- nied that the sunlight strikes the house at differ- ent angles during the day and likewise at diflEer- ent seasons of the year, thus producing considerable variation in the amount of light reflected. To obvi- ate this, houses should be built with greater roof angles, a plan which will insure less reflection and thus allow a greater amount of light to penetrate. During January, for instance, whien the normal sun- light is naturally less, glass placed at an angle of 58 Diseases of Greenhouse Crops 60 degrees will absorb far more light than if placed at angles of 10 or 30 degrees. It has been the general belief that the light in the hothouse was greatest nearest to the glass. Ex- perience has disproved this. Modem houses are built larger, which means a greater distance between glass and plants. Effects of Various Colored Lights That plants require light for their normal de- velopment and for the proper performance of their function no one doubts. Crops grown outdoors naturally receive their light from the sun's rays. Plants within the greenhouse do not always receive the rays of the sun in a normal way. As a result, the health of these plants may often be impaired, or the quality of the product greatly affected. The researches of Flammarion* on this subject are of particular interest to the greenhouse man. Temperature Influenced by the Color of THE Glass Flammarion has shown that temperature is af- fected by the color of the glass. Houses differen- tiated by the following sorts of colored glass were tried: blue, approaching closely to violet; red tra- versed by a little orange; green and ordinary white glass. These four houses were placed side by side * Flammarion, Camille. Experiment Station Record 10: X03-114, Light in Greenhouse Culture 59 and equal conditions of care and culture were ob- served in all of them, approaching natural condi- tions as nearly as possible. The temperatures in these houses are given in Table 7. Table 7 Time of day White Red Green Blue 7:30 A.M. Degrees 320 Degrees 31.0 Degrees 30.7 Degrees 295 8:30 A.M. 40.0 39-5 370 35-0 10:30 A.M. 49.0 46.0 415 40.0 12:30 Pa*. 42.0 40.0 390 38.0 2:30 P.M. 41.0 40.5 40.3 40.2 4-.30 P.M. 30.0 300 300 30.0 It is evident that the ability of the glass to absorb the sun's rays determines the heat in the hothouses. All rays are able to pass through white glass, which explains why the highest temperatures were found in this house. The lowest temperatures were foimd in the blue house, blue having the greatest absorb- ing power. It is striking that the temperature was apparently the same in all tibe hothouses during, the cloudy weather and when the sun's rays did not penetrate directly. Plant Growth Influenced by the Color of THE Glass Experiments on sensitive plants showed the fol- lowing results: Plants placed in a red house de- 6o Diseases of Greenhouse Crops veloped a height fifteen times as great as that in the blue house, where practically no growth was made. The red light in this case acted as a fertilizer. Moreover, the sensitiveness of the plants grown in the red house had increased considerably. The slightest movement or breath was sufficient to cause the leaflets to close, or the pedicels to droop. The sensitiveness diminished under the white or green color, while under the blue glass the sensitiveness was almost lost. The plants in the red house were first to bloom. In the white house they increased in stockiness and in vigor, but did not seem to in- crease in height. The plants in the house with the red glass possessed foliage which was lighter than those grown in the white house, while under the blue glass the foliage was much darker. After three months the height of the plants in the different houses was as shown in Table 8. Table 8 Date Ret While Green Blue June 13 Meter 0.030 Meter 0.030 MeUr 0.030 Meter 0.030 July 22 0.230 0.120 0.080 0.035 August 16 0.380 0.240 O.IOO 0.035 August 30 0.470 0.270 O.IOO 0.035 October 12 0.500 0.380 O.IOO 0.035 From the preceding table it is seen that the plants in the hothouse with the red glass attained Light in Greenhouse Culture 6i greater height and exhibited more sensitiveness than those in the white house. The sensitive plants in the green hothouse made a littl« headway at first and then came to a standstill. In the hothouse with the blue glass practically no headway was made. In comparing the weight of the plants in the various hothouses with that of the height as previ- ously mentioned, the results will be found to be diflEerent. This is clearly seen in Table 9. Table 9 Hothouse Weight of Stems and Learns Weight of . Average Leaf DiamOer Stem White Grams 8.400 Grams 0.600 Mm. 3.0 Red 4.600 0.250 2.0 Green 0.300 0.150 1.5 Blue 0.150 0.095 I.O It is very curious to find that the plants in the red hothouse, although the highest, were not the heaviest. The weight was almost double in the white hothouse, although in height the plants did not compare to those in the red hothouse. Experiments on lettuce, similar to those on the sensitive plants, yielded like results. Lettuce grown in the white hothouse produced large thick leaves with well rounded heads, in fact the plants here did not differ from those grown in the open. Let- tuce grown in the red house was drawn, its leaves 62 Diseases of Greenhouse Crops long, straight, blanched and drooping. Those grown in the hothouse with green glass made a slight growth, but the leaves were more curled than those in the red house. In the blue hothouse, the lettuce plants added only a few leaves, without increasing the height attained in the first two weeks (fig. 9, Experiments on peas and beans yielded similar results. In both plants the normal and most vigor- ous growth was found to occur in the white hot- house. The plants in the red hothouse were taller but thinner, while in the blue hothouse the minimum of growth occurred. The beans bloomed and fruited equally well in the white and in the red hothouses. In the green and in the blue houses the plants soon died. With the peas, blooming and fruiting seemed to be normal both in the white and in the red hot- houses. In the house with the green glass, the peas remained in bloom for three weeks, but did not fruit. In the blue house, the peas failed to bloom altogether. Experiments with ornamental plants, such as Coleus, yielded similar results. The Coleus in the ^hite hothouse produced a normal well developed plant. In the red house there was an increase in height with a decrease in foliage. In the green and blue hothouses there was very little develop- ment (fig. 9, a-h.). i k 1 Fig. 9. Action of Different Light Rays ON COLEUS AND ON LeTTUCE. u. Full radiation, h. red rays, c. green rays, d. blue rays, e. open air, f. subdued li^ht, g. diffused light, h. very dim light, i. blue light, /. green li^ht, k. red light, /. white light (0-/ after Flammarion) . Light in Greenhouse Culture 63 Root Development Influenced by the Color of the Glass It has already been seen that different rays of the solar spectrum may modify the parts of the plant above ground. The same effects may also appear in the root system of such plants. The root system is considerably smaller in the red hothouse than it is in the white hothouse. In the hothouse with green glass, the root system is very poorly developed, while in the blue there is almost no root system. Anatomy of the Plant as Influenced by Dif- ferent Rays of Light As we have seen, different rays of light are capa- ble of influencing the growth of plants. The same is also true of the structure of plants. Flammarion has found that sensitive plants, for instance, when grown in a white hothouse, possess a thicker epider- mis, more numerous wood fibers in the stem, and the pith was much less developed than was the case with similar plants grown in red, green or blue hot- houses. Effect of White and Colored Light on Trans- piration The effect of various lights on transpiration is shown in Table lo. 64 Diseases of Greenhouse Crops Table lo Color Weight Leaf Wnght of Transpired Water Water Trans- pired per Gram of Leaf Grams Grams Grams Red 0.135 0.208 1.540 YeUow 0.102 0.230 2.254 Green with some yel- low rays 0.095 0.065 682 Violet 0.080 0.024 0.302 It is thus seen that the greatest transpiration takes place under the yellow light, and the least under the violet. Effect of Various Light Rays on the Color of Plants It is well known that the green color of leaves which is due to chlorophyll can only be produced in the light. Other plant colors such as red, yellow, blue, may be due to the presence of colored pig- ments, or to color in the cell sap itself. That light and not temperature is capable of changing the colors in plants has been proven by the investigations of Flammarion. He found that lilac blossoms in a white hothouse became pink, and in red, green and blue hothouses the blossoms became white. If the lilac blossoms already colored are placed under a dark bell jar, they will turn from pale blue to clear red violet. This change of color Fig. 10. Action of Different Light Rays ON THE Color of Plants. a. Red flowered Crassula in sunlight, h. same in darkness, c. Alter- nanthera amoena full radiation, d, same under red rays, e. geranium leaves full radiation, f. same under blue rays, g. green rays, h. red rays iorh, after Flammarion). Light in Greenhouse Culture 65 is not due to temperature. It is due solely to the eflFect of various light rays. Lilac blossoms, for in- stance, if enclosed in a dark chamber will become discolored, irrespective of surrounding temperatures. Coleus plants grown in a white hothouse will produce leaves with the normal amount of red color and pigmentation. In a red hothouse, the red pig- ment of the Coleus decreases, the leaves are more spread, and their form is changed. Coleus grown under green-colored glass produces leaves of small sizes, the pigments almost disappear, and ^ve place to a yellow coloration. The same is true also when Coleus is grown under blue glass. In this case, however, the red pigments disappear almost com- pletely (fig. 9, a-d.). In substantiation of the fact that light is capable of transforming plants, Flammarion refers us to the following experiment: Coleus plants may gradually be transformed when grown under a slightly diffused light through a gar- den frame, in diffused light, and in still weaker light. The plants grown in the open are of course normal. The most curious transformation occurs in the diffused light. Here the leaves enlarge con- siderably and the red pigments diminish in the cen- ter. Under a weak light the Coleus leaves become stunted, and the color changes from poppy red with a dark edge to yellow with a light green edge (fig. 9, e-h.). Purple leaves of Alteraanthera amena will become green under red glass. In the open, gera- nium leaves possess a reddish brown tone. This color changes imder red, green or blue rays (fig. lo, a-h.). 66 Diseases of Greenhouse Crops These experiments seem to indicate that light is of itself able to modify plants. Effect of Light on Disease Resistance It has already been seen that light is an important factor in plant culture. It alone seems able to change the form of a plant as well as its color. Moreover, the resistance of a plant to a disease may be modified by light. Damping off, for instance, a prevalent disease in greenhouses, is more virulent on dark cloudy days, when the light in the hothouse is abnormal and weak. A temporary change in the normal functions of the metabolism of the plant occurs and is followed by a sudden lowering of vitality. The greenhouse man cannot overlook the importance of the light requirement of plants under glass. Experience has shown that white glass is the only one capable of furnishing the necessary light rays to the plant. Needless to say, that only the best quality should be secured, for economies in the quality of glass may not always be the wisest nor the cheapest in the end. Electro-Culture The field of greenhouse culture is a plastic one. Electricity is undoubtedly capable of influencing plant growth. The greenhouse man who is conscious of the possibilities of control in his plastic domain will not neglect this phase of plant culture. Light in Greenhouse Culture 67 Effect of Electric Light It has always been a questitwi whether growth under hothouse conditi(His could not be hastened by using artificial light at night. The work of Rane* has shown that such is the case. The beneficial effect on lettuce seems to be cspe- dally marked for the Grand Rapids variety first, next for the Hansc«i and thirdly for the Tennis Ball, the only three varieties experimented on by Rane. The lettuce in the house lifted with elec- tricity seemed more erect, vigorous, and the soil freer from damping off and rot-producing organ- isms. This is indeed an important consideration. Moreover, the lettuce in the electrically lifted house matured about twelve days earlier than that grown otherwise. Greenhouse spinach, like lettuce, seems also to be benefited by electric light at ni^t. On the other hand, cauliflower reacts poorly to this treatment. Although the plants are taller, the qual- ity of the head is of an inferior grade. Radishes develop more tops than roots. The practical- minded greenhouse man will use electric light at ni^t to induce extra stimulation for those green- house crops that respond favorably to it. The cost of installing the system certainly cannot be consid- ered as a real drawback. Electricity in these days may be obtained at a reasonable price. This is es- pecially true of greenhouses situated near larg^ •Rane, F. W, West Viig^a Agr. EipL Sta. Bui. 37, VoL 4, No. i: 3-*7> 1894- 68 Diseases of Greenhouse Crops cities. But more extensive investigations are needed to convince the grower of the practicability of the attempt. Effect of Shading It has been shown in the previous chapter that certain light rays, such as green or blue, are detri- mental to plant growth. On the other hand, the normal sun rays from outdoors or as they come through white glass are most conducive to normal plant culture. The practical man, however, real- izes that at certain times of the year, especially dur- ing the summer months, the white glass must be shaded to prevent an excess of sunlight. This is accomplished by whitewashing the glass. That this procedure is necessary no one can question. How- ever, it must be admitted that the method itself is still a crude one, inasmuch as the various plants in the hothouse are subjected alike to the same amount of shading. Shantz* has shown that while a certain amount of shading is beneficial to plant growth, yet not all plants are benefited alike by this treatment. Effect of Different Light Intensities on Plants The work of Shantz distinctly shows that all plants do not tolerate the same amount of shading. To prove this he grew various crops in a bed cov- • Shantz, H. LeRoy, U. S. Dept Agr. Bur. PI. Ind. Bui. 379: 7-29, 1913. Light in Greenhouse Culture 69 ered with cloths of different textures. The arrange- ment of the cloth and the amount of light penetrat- ing it are shown in Table 11. Table 11 Method of Determining the Effect of Different Light Intensities SatioH of Bed I 3 3 4 f S 6 Cloth Used Black Duck Light Canvas Cloth (.Black) Cham- bray Light Cham- bray Voile No Cover Fraction of normal li^ht •capable of passing through cloth 1/93 or n/93 I/IS or n/is 1/7 or n/7 I/S or .jin/s 1/3 or [n/3 I or n As an explanation to Table 11, in referring for instance to column marked 2, n/i$, we mean the second section of the bed where light canvas cloth (black) was used for shading, and where the light capable of passing through was equivalent to 1/15 or «/i5, / or n represents the normal. The same interpretation is given to the other sections of Table 11, all of which really correspond to the sections of the bed experimented with, it being remembered that /■ or « represents normal light. Effect of Different Light Intensities on Lettuce According to Shantz, lettuce could not grow in section i under «/93 illumination, as the seedlings died as soon as the reserve food material in the cotyledons was consumed. In section 2, n/15 70 Diseases of Greenhouse Crops illumination, growth was barely possible. The plants in this case were emaciated and worthless. It seems, therefore, evident that lettuce cannot stand shading where the light is reduced to n/\$. The greatest amount of gain is made by lettuce when the intensity of the light ranges between n/7 and n/5. At this point the stimulation is greater than in those grown under normal light or even at n/l. In full light lettuce plants are smaller than in n/'] or «/5 light. In flavor, a very slight change only may be noticed between plants grown under full light and those receiving n/l light. However, un- der «/5 illumination the strong taste seems to dis- appear entirely. When the light is reduced to w/y the flavor seems to improve even more. Moreover, m this case the plants acquire the particular form of growth required by the market more consistently than do those that are produced in brighter light. Effect of Different Light Intensities on Radish Young radish seedlings seem capable of standing about 30 days under n/93 illumination. At the end of that time, however, they die. In «/i5 light there is almost no growth. The best gains seem to be made under a light of «/2 or n/^- In this respect, the shade tolerance of the radish is somewhat simi- lar to lettuce. However, the effect of shade is not noticeable in the flavor of the radish. From the above evidence it is apparent that plant growth is assisted by shading, the degree of which Light in Greenhouse Culture 71 must be worked out for each specific crop. Ordi- narily, imder greenhouse conditions, shading k ac- complished by means of whitewashing the glass of the hothouse. It would seem more desirable to use chambray, light chambray or voile cloth instead of whitewashing. The cloth could be installed on a system of rollers, so that when shading is necessary it could be spread out on the glass and when not needed it could be rolled up again. This would enable the greenhouse man to retain the full amount of normal light on cloudy days, an advantage which cannot be obtained when the glass is whitewashed. The substitution of cloth for whitewashing offers a good field of experimentation, both for the labora- tory and for the practical man. Heat Requirement The heat requirement of indoor crops demands the closest attention and study. As is well known, no two crops require the same temperature for their maximum development and production. Moreover, the same plant requires different temperatures in its various stages of growth. To appreciate thor- oughly the relaticmship of heat to plant life, we may liken the plant to a steam en^ne. With very slight steam pressure, the engine remains "dead," because it is not able to overcome the friction of its own parts and hence is capable of no work. With the proper amount of steam pressure, the eng^e is capable of a maximum amount of work. 72 Diseases of Greenhouse Crops However, if an excess of steam pressure is used, the engine under an excessive strain will break or explode. The same is true with plants. A low temperature may not sufEce to awaken the active life processes. With increased temperature, the plant becomes capable of maximum activity. Tem- perature beyond the normal requirements causes it to suffer or even to die from weakness and disease. The ideal development with forced plants is pos- sible only if we consider the relationship of the soil temperature to that of the air. For instance, the bum of lettuce is brought about by rapid evapora- tion of moisture from the leaves at a time when the roots are unable to supply this excessive demand of water. If the soil is cold, or its temperature dif- ferent from that of the house air, the roots will be unable to supply fast enough the water needed by the foliage. This will result in their collapse or burn- ing, and the ruin of the lettuce crop. The proper temperature requirement for each crop will be taken up when we consider further the cultural require- ments of each. CHAPTER 5 MOISTURE AND WATER REQUIREMENTS Moisture here means the humidity present in the hothouse atmosphere. The importance of this sub- ject is as yet little appreciated by the practical man. The investigations of Blake* on the moisture re- quirements of roses point to the urgent need of similar experiments, on other commercial hothouse crops. In the greenhouse, temperature and humidity rank with food in their importance to the plants. Ejfect of Humidity on Rose Foliage. Frequently when a greenhouse crop fails, the soil, the fertilizer or the water receives the burden of the blame. Lit- tle does it occur to us that the cause of the failure may be due to improper adjustment of humidity to temperature and watering. That each crop requires diflFerent humidity conditions is well conceded. The maidenhair fern, for instance, will not thrive in a house with a dry atmosphere, a condition which is ideal for other plants such as ornamental cacti. With roses a low humidity tends to reduce the size of the leaves, and the latter become "hard" and lose their flexibility. Again, vigorous, dark green foliage indicates a proper degree of humidity. •Blake, M. A., New Jersey Agr. Expt. Sta. Bui. 277: 3-55, 191s- 73 74 Diseases of Greenhouse Crops Relation of Temperature and Humidity in THE Greenhouse The investigations of Blake show (Table 12) that the humidity decreases in direct proportion to an increase in temperature. The opposite occurs when the temperature is lowered. Table 12 Humidity as Affected by Temperature Date, 1914 Outdcor Wealhtr CoHdUions Time Vmrna- Urn Beat Temper- lature in 'Bouii Btmtdily 11:00 A.M. Yes On 70 73 Feb. II Fair 10:30 AJI. Yes Off 64 go Feb. 12 Fair lyo PJJ. None On 62 72 4:00 P.M. None On 64 Feb. 13 Fair, cold II-.30 A.H. None Off 68 80 Feb. 13 3-.30 P.M. None On 6S 7S Feb. 14 3:15 P.M. None Off 71 82 Feb. 14 5:00 P.M. None On 61 69 Feb. 16 Fair 2:00 P.M. Yes Off 6S 95 Feb. 16 S:oo P.M. None On 63 79 Feb. 17 • Rain 8:00 AJJ. None On 60 89 Feb. -17 Rain 1:00 PJI. Yes Off 67 95 Feb. 18 Snow and rain. . . . 8:00 A.M. None Off 67 90 Feb. 18 Snow and lain. . . . 3:45 P-M. None Off 64 86 Feb. 20 Fair 11:00 A.M. Yes Off 67 90 Feb. 20 Fair 4:30 PJl. None On 64 85 Fair 8:00 A.H. None On 71 65 Feb. 2X Fair mo P.M. Yes Off 72 ! 78 Moisture and Water Requirements 75 From Table 12 it is evident that heat lowers the humidity. It is also to be noted that the decrease in humidity is rapid on bright days even when most cold. It is to be further noted that not only the heat, but the ventilation of the house during the day when the heat is turned on in the pipes, tends to reduce the humidity still further. Rose growers, for instance, are aware that at the approach of spring the plants suddenly improve greatly. This is generally attributed to lon^r and brighter days. However, according to Blake, this change is due to an increase in humidity in the hothouse due to the shutting ofiF of the heat in the pipes. Effect of Humidity on Greenhouse Crops For further information on this subject, we have to refer again to the researches of Blake. He finds that the American Beauty rose, for instance, as a result of insuflBcient humidity fails to produce new shoots from the base of 'the plant. Moreover, the foliage, except at the tips of the growing shoots, be- comes hardened and toughened. The older leaves turn yellowish and fall oflE prematurely, leaving bare stalks. As a result of this the younger and smaller rootlets die out. Blake also found that a high humidity tends to increase the size of the foli- age, and the flowers seem to be likewise favorably affected. With low humidity the leaves of small rose plants wilt on bright days, even thou^ the soil is kept moist. Frequently the leaves turn black. 76 Diseases of Greenhouse Crops which is really a fonn of sunburn. This is un- doubtedly caused by the dryness of the atmosphere in which the moisture in the leaves is given off faster than the roots can supply it. Humidity as Affected by Walks in the House There seems to be a tendency among modern greenhouse men to build benches and sidewalks of cement. While this may be very desirable from a hygienic viewpoint, it is objectionable for the main- tenance of the proper degree of humidity. It is extremely difficult to raise the humidity of a house with cement walks. This is true even when water is applied to the walks and sprinkled on the plants. In houses devoted to roses and similar plants, where it is desirable to maintain a humidity of at least 75 per cent., cement walks become quite objectionable; cinder walks are to be recommended instead. Ce- ment walks may be readily transformed by cover- ing them with a layer of six inches of cinders. This covering will make it possible to maintain a higher and more uniform humidity. Humidity is also an important factor in the heat- ing of glass houses. The greater the humidity the greater is the evaporation of moisture, and the greater is the amount of heat required to maintain a uniform temperature. Without proper attention to these conditions, the hothouse crop may be doomed to failure. Fig. II. a. Sling psychrometer, an instrument used to determine the relative humidity in the air, b. case cover. Moisture and Water Requirements 77 Humidity Determination in the Greenhouse Perhaps the quickest and safest way of determin- ing the relative humidity of the air in the hothouse is by means of a sling psychrometer (fig. ii.). This instrument is very simple in design. It con- sists of a wet and dry bulb thermometer attached to a wooden or metal support. The handle arrange- ment permits the instrument to be whirled in the air while taking the reading. The wet bulb ther- mometer is covered with muslin and is thoroughly moistened by being plunged into a cup of water which should be of the same temperature as that of the air of the hothouse. Method of Determining Humidity After wetting the muslin of the wet bulb ther- mometer, the instrument is whirled steadily for a few seconds and the reading of the wet bulb thermome- ter noted. This whirling is repeated several times, until the reading of the wet bulb thermometer is constant. At this stage, the difference of tempera- ture between the wet and dry thermometers is re- corded. After this difference has been obtained, we turn to Table 13 to get the exact reading of the relative humidity of the hothouse air. To make this clear to the reader, let us take a specific exam- ple. Suppose that the reading of the wet bulb ther- mometer was 64 degrees, and that of the dry bulb thermometer 62 degrees. This, then, will give us 78 Diseases of Greenhouse Crops a difference of two degrees between the wet and the dry buib thermometer. Let us now refer to the table under the column Dry bulb thermometer de- grees, where it is marked 62 degrees. Read across Table 13 under the column depression of wet bulb thermometer in degrees until the column indicates a difference of two degrees. In this case it is the fourth column. The resultant figure, 89, will be the relative humidity of the hothouse air. In other words, a temperature of 62 degrees of the dry bulb thermometer with a difference of two degrees of the wet bulb thermometer will give a reading of 89 relative humidity of the air. In like maimer, and by referring to Table 13, which should be hung up at a convenient place in the hothouse, the relative humidity of the house may be obtained. There are other simpler instruments by means of which the reading of the relative humidity may be obtained directly without the use of tables. The Mithoff hygrometer, for instance, is a type of such an instru- ment. However, they may readily get out of com- mission, and thus becrane unreliable. Watering The importance of water for greenhouse plants cannot be too emphatically stated. It has been truly said that "he who does not know how to water plants does not know how to grow them." Water is essential to plant life. It has been intimated that some crops evaporate from the leaves an amount Moisture and Water Requirements 79 Table 13 Relative Humidity, Per Cent. — Fahrenheit Tem- peratures. Pressure 30.0 Inches Dry Bulb mometer Degrees SO 51 53 53 54 55 56 57 58 59 60 61 6a 63 64 65 66 67 68. 69 V> 71. 12. 73 74 75 76 77. 78. 79. So. Depression of Wet Bulb 96 97 97 97 97 97 97 97 97 97 97 97 97 97 97 98 98 98 98 98 98 98 98 98 98 98 93 94 94 94 94 94 94 94 04 94 94 94 94 95 95 95 95 95 95 95 95 95 95 95 95 96 96 96 96 96 96 1. 5 91 91 91 91 91 92 92 93 92 93 93 93 93 93 93 93 93 93 93 93 94 87 87 87 87 88 89 89 89 89 90 3.5 83 84 I* 84 85 85 85 85 85 86 86 86 86 87 87 87 87 87 88 88 88 88 88 88 89 89 89 89 89 89 89 3.0 80 81 81 81 83 82 82 82 83 83 83 84 84 84 84 85 85 85 85 85 86 86 86 86 86 86 87 87 87 87 87 4.0 77 78 78 78 79 81 81 81 82 82 82 82 83 83 83 84 84 85 85 85 85 74 75 75 75 76 76 76 77 77 78 78 78 79 79 79 80 80 80 80 81 81 81 82 82 82 82 82 83 83 S3 83 4-5 73 73 74 74 75 77 78 78 78 79 So 80 81 81 81 81 5.0 67 68 69 69 70 73 73 74 74 74 75 75 75 76 76 77 77 77 78 78 79 5-5 6s 66 66 67 68 68 69 69 70 72 73 73 74 74 74 75 75 75 76 76 76 77 77 77 77 6.0 61 62 63 63 64 65 6S 66 66 67 68 68 69 69 70 72 72 73 73 74 74 74 74 75 75 75 6.5 58 59 60 61 61 62 63 63 65 65 6S 66 67 67 68 68 69 69 70 72 72 72 73 73 74 7.0 55 56 57 58 59 59 60 61 61 62 63 63 64 65 66 66 66 67 67 68 68 69 69 69 70 70 71 71 71 72 8o Diseases of Greenhouse Crops Table 13 (continued) Relative Humidity, Per Cent. — Fahrenheit Tem- peratures. Pressure 30.0 Inches Thermometer in Degrees JS 8.0 8.5 9.0 9.5 10. 10.5 II. 11.5 12.0 12. 5 13.0 13.5 14.0 14.5 rs.o 15. S S2 49 46 43 41 38 35 32 29 27 24 21 18 16 13 10 8 53 SO 47 45 42 39 36 34 31 28 26 23 20 17 15 12 9 54 51 49 46 43 40 37 3S 32 29 27 It 22 19 17 \t II SS 52 50 *Z 44 41 39 36 33 31 28 23 20 18 13 56 53 SO 48 45 42 40 37 35 32 29 27 24 22 20 17 15 57 54 51 49 46 43 41 38 36 33 31 28 26 23 21 19 16 *Z 55 52 so *Z 44 42 39 37 34 32 30 27 25 22 20 18 S8 55 S3 50 48 41 43 40 38 35 33 31 28 26 24 22 19 59 56 54 SI 49 46 44 41 39 37 34 32 30 27 25 23 21 59 57 55 52 49 47 45 42 40 38 35 33 31 29 26 24 23 60 *! 55 53 SO 48 46 43 41 39 37 34 32 30 28 26 23 61 58 56 54 SI 49 47 44 42 40 38 35 33 31 29 27 2S 61 59 57 54 52 SO 47 45 43 41 39 36 34 32 30 28 26 62 60 H Si S3 SO 48 46 44 42 40 37 35 33 31 29 27 63 60 58 56 53 51 49 47 45 43 41 38 36 34 32 30 38 $3 61 59 S6 54 52 SO 48 46 44 41 39 37 35 33 31 29 S* 61 59 S7 SS S3 51 48 46 44 42 40 38 36 34 32 30 64 62 60 58 S« 53 51 49 47 45 43 41 39 37 35 33 31 S* 62 60 S8 56 54 52 50 48 46 44 42 40 38 36 34 32 6s 63 61 59 57 55 53 SI 49 47 45 43 41 39 37 35 33 66 s* 61 5" 57 55 53 SI 49 48 46 44 42 40 38 36 34 66 A* 62 60 58 56 54 52 SO 48 46 45 43 41 39 37 35 67 s* 63 61 59 57 SS 53 SI 49 47 45 43 42 40 38 36 S^ 6s 63 61 ?» S7 55 53 51 50 48 46 44 42 40 39 37 67 65 63 61 60 58 56 54 S2 50 48 47 45 43 41 39 38 68 66 t* 62 60 58 56 54 S3 51 49 47 45 44 42 40 39 6S 66 s* 62 61 59 57 55 S3 51 SO 48 46 44 43 41 39 69 V 65 63 61 1" 57 56 54 52 SO 48 47 45 43 42 40 ^ 67 6s S^ 62 60 sf 56 54 S3 SI 49 47 46 44 43 41 69 68 66 64 62 60 58 57 55 53 51 SO 48 46 4S 43 4a 70 68 66 64 62 61 S9 57 55 54 52 SO 49 47 45 44 42 Moisture and Water Requirements 8i Table 13 (continued) Relative Humidity, Per Cent. — Fahrenheit Tem- peratures. Pressure 30.0 Inches Dry Bulb Thamometer SO. SI. sa. 53. S4. SS. S6. 57. S8. 59. 60. 61. 63. 63. 64. 6S. 66. 67. 68. 69. TO. 71. 7». 73. 74. 7S. 76. 77. 78. 79. 80. Oeinessioii of Wet Bulb 16.0 41 16.S 39 38 ; 18.0 18.S ta 33 a4 as a6 32 33 34 34 35 36 *S a? 38 39 39 35 30 30.5 W 33 34 35 35 36 82 Diseases of Greenhouse Crops Table 13 (continued) Relative Humidity, Per Cent. — Fahrenheit Tern- peratures. Pressure 30.0 Inches Thermometer in Degrees 31.0 21. S 32.0 23. S 23.0 33. s 34.0 34. S 3S.0 3S.S 36.0 36.S 37.0 37. S 38.0 38.5 I 3 % 7 9 10 13 13 14 IS 17 iS 19 30 31 33 33 34 3S 36 I 3 % 7 9 10 II 13 14 15 16 17 IS 30 31 33 33 33 34 I 3 4 5 I 10 II 1-3 *3 ?i 17 18 19 30 31 33 33 3 4 5 7 8 9 II 13 13 14 IS 19 30 31 33 3 3 1 8 9 10 13 13 14 17 18 19 20 3 3 i 8 9 10 II 13 14 IS 16 17 18 19 3 3 S 6 7 9 10 II 13 13 \% 17 18 I 3 % 7 8 10 II 13 13 14 IS 16 "i 3 % 7 8 9 II 13 13 14 IS I 3 4 S 7 8 9 10 II 13 14 I 3 4 S \ 9 10 II 13 I 3 4 5 6 8 9 10 II I 3 4 i 8 9 10 I 3 4 5 6 7 9 I 3 4 i T I 4 s Moisture and Water Requirements 83 of water equal to about three hundred times the weight of the dry matter which they contain. The amount of water in the soil is also an important con- sideration. The more water a soil contains the less air it will have. The presence of too much water in the soil often brings about serious complications in the health of plants such as suffocation of ^e roots, weak growth and a loss in power of resistance. The improper use of water may affect the physi- cal structure of the soil and injure the plants. The careless dadiing of water on the surface of hothouse benches will compact and puddle the soil, and tend to wash down the smaller grains to the bottran, changing thereby the capacity of that soil to retain air or heat, and thus indirectly affect the health of the plants. Greenhouse plants depend on irrigation for their water entirely. Surface watering is still in use by the majority of hothouse men. But at best, this method often does no more than pack the soil in- stead of saturating it. Moreover, while safe enough for the experienced grower, it becranes extremely unsatisfactory when entrusted to careless or inex- perienced labor. SUBIRRIGATION It has been hinted previously that subirrigaticm has not foimd general favor with greenhouse men. Yet this has proved both experimentally and in practice to be far superior to any other form of 84 Diseases of Greenhouse Crops greenhouse irrigation. In subirrigation water is ap- plied through tiles undergroimd. Effect of Subirrigation on Vegetable Crops. In- vestigations by Rane* have clearly shown that pars- ley, tomatoes, long rooted radishes and spinach are greatly benefited by subirrigation. Lettuce, espe- cially, seems to be most favorably influenced by this method of watering (fig. 12, a-c). Little is known of the eflFect of subirrigation on flowering plants. In- vestigations along those lines are especially desirable. From the health viewpoint, subirrigation should appeal to greenhouse men. Where lettuce drop is prevalent subirrigation seems to check it materially. The same is also true of damping oflE. In the greenhouse, subirrigation may be adapted to any form of bed used, whether raised or solid. In either case the bed should be practically water- tight. To prevent the rotting of wooden beds Taf 1 1 recommends coating the inside of the beds with a cement made of one part of water lime and three of sharp sand. This is made into a thick paste and spread over the surface about one-fourth of an inch thick. For a bed with tile or slate bottCHns a simi- lar covering will render them sufficiently tight. With wooden benches it is desirable that the sup- ports be close enough to prevent sagging of the beds. In case of solid beds, a tight bottcMn about eight inches below the intended level of the bed is •Rane, F. W, West Virginia Agr. Expt Sta. Bui. 33: 255-270, 1893. t Taft, L. R., Year Book, U. S. DepL of Agr.: 233-246, 1895. SUB- o ORDINARY omimw 5UB- ?f ORDINARY " ii iiP I IM|.il"| i Fig. 12. Effect of Subibkigation on Lettuce. a, Boston curled, b. Frankford head (o-c after Rane, F. W.). Moisture and Water Requirements 85 necessary. If the subsoil is a stiff clay it may be de- sirable to spread an inch of gravel. After thoi^ ou^y ramming it is covered with a thin layer of the cement as described above. Overhead Irrigation This method is in greater use than any other prac- tice of greenhouse watering. The advantages claimed for it are the cheapness of installation and the more uniform way in which the water is applied. By this method, too, the dry atmosphere of the house can be quickly changed. This is especially desirable during the hot summer days. The disadvantages of this system are the packing of the surface soil and the en- couragement of disease through the excessive mois- ture applied to the plant. Ventilation Next to watering, ventilation is of utmost im- portance frcttn the health viewpoint. Many of the plant diseases which are confined to the greenhouse are encouraged by improper ventilaticHi. The lack of it is as harmful as an excess. The practical grower will give this careful thou^t and consideration. As a rule, plenty of ventilatitm should be given whenever weather ctaiditions permit it, avoiding, however, draft and strcaig air currents. CHAPTER 6 BREAKING THE REST PERIOD OF PLANTS The object of greenhouse culture is to grow cer- tain crops or blooms at a time and season when these cannot be produced outdoors. All plants un- dergo a period of rest. Bulbs, for instance, enter their resting state when the leaves all die. No mat- ter how cold, warm or wet, bulbs will not grow again before the fall. Howard* has found that it is very difficult to shorten this dormant period, at least during the earlier phases of the rest. He further found that of all treatments, drying, followed by injection with ether and Knop's solution (made up as follows: Calcium nitrate i gr., magnesium sul- phate 25 gr., acid potassium phosphate 25 gr., and water 1 liter.), and combinations of these were most effective in shortening the rest period of bulbs. The injection may be accomplished by piercing the bulb with a hypodermic needle. Herbaceous perennials, too, like the bulbs, undergo a rest period. Frost, drying, and ether appear to be the most effective agents in breaking this rest period. To treat plants with ether, a galvanized iron chamber is preferred. The latter as used by Howard is shaped like a cylin- * Howard, W. L., Missouri Agr. Expt. Sta., Research Bui. 15: J-*Si 1915- 86 Fig. 13. Effect of Etherization on Plants. b. Baptisa australis, 24 hours; c. check; a. 12 hours, f. Stokesia cyanea, check, d. etherized 24 hours; e. etherized 12 hours (a-f after Howard, W. L.). Breaking Rest Period of Plants 87 der, with a diameter of about two feet and is made in two sections, each about three feet in length. The lower section is fitted with a bottom and at the top, aroimd the rim, with a groove which is filled with fine sand. The rim of the upper section flares out) so as to accommodate a lid. The latter fits in ti^tly by being forced down in the sand. The second sec- tiwi of the cylinder is like the first, except that it is bottomless. When treating a large number of plants at one time, the second section is placed uprai the first, the lower end being forced into the sand. The ether is poured in throu^ an opening in the lid, which may be tightly closed by means of a screw cap. The amount of ether used is at the rate of 40 grams to each 100 meters of space. The lid is weighted with bricks to prevent its being pushed off by the ether vapor. Treatments should preferably be ^ven in the afternoon, or where there is no likelihood of changes of temperatures. The results of the treatment are summarized by Howard in Table 14 on following page. From Table 14, it is seen that with certain plants etherization breaks the rest period and hastens growth (fig. 13, a-f.) while with others the treatment has the opposite effect. In his investigations How- ard* further found that the rest period of a large number of woody plants may be largely overcane by ether treatment (fig. 14, a-b.). On the whole, how- •Howard. W. L, Missouri Agr. Expt Sta, Research Bui. 16: 3-27, 1915. 88 Diseases of Greenhouse Crops M n < Jig (qui II .S S 1« s 5« s. ^14 15, S l|s| ll-'^l iS 5. t:,0 Q |l-5| ;; •In aoo t* I no n 4- 4- O in<0 •^00 i<0 +■« |t*M»«.^n 4-laioo wiflPi iww"* '*X ** ' itJ^'/TUn t ♦* I *♦ ;p+*+* I ;3^** -SI I ^A| I ^■Oi I I WVlMOt -*-n|lo ooOiOt lw>«l 5ISI -^1 I l^^l I -^1 I I I -^85 I l-^l 8 ai?l -iiia-il II 1 1^1 -III -&-IS-II ^3^81 -^ ^n H -III -^ssiiaii ^H"S' *"H ""'"' ft I M « ei ^ ei on c« I I M met ^e* n fj, ^^ 4^ 44 4444 4444 J j 00 00 o I O ooo I ^o+-n Ot 00 I ^- 1 00 >-u3ot r»^^H-ao 44 44*H I ^ M44 I M Ot** M I I M 4+44 44M M 444-l>4'444-4^ 44 44 ^.- 4+44 +-00 M «*« M M M e« « n TC III II I I I *♦ 44 44 :>4 i-S •• B :2 ;l : i- iFllf a •■S-o & -oft : a -si a -ag aa '■OlaS'ES uuQaanon ■I ^ •a s "a Fig. 14. Effect of Etherization on Hybiscus Syriacus. a. Etherized 48 hours, b. check (after Howard, W. L.). Breaking Rest Period of Plants 89 ever, the use of anesthetics is still in the experi- mental stage, although much that has been already discovered could be applied with great advantage commercially. PART III DISEASES OF GREENHOUSE VEGETABLES CHAPTER 7 NATURE OF PLANT DISEASES The successful greenhouse operator will realize the necessity of recognizing readily any plant dis- ease. Very often this is overlooked and attention is attracted only when the trouble takes the form of an epidemic, and a large number of plants are thus carried oflE by it. Plant diseases are usually of four kinds : 1. Those of a mechanical nature. 2. Those brought about by physiological dis- turbances or imfavorable environment. 3. Those brought about by parasitic flowering plants, fungi or bacteria. 4. Diseases the cause of which is unknown. A familiarity with the symptoms of diseases will enable us to determine the contagious nature of the trouble and often the methods of control to pursue. The following outline* briefly summarizes the prin- cipal symptoms of disease in plants : 1. Discoloration or change of color, a. Pallor, yellowish or white instead of the nor- mal green. 'Adapted with slight modifications from Heald, F. D., Texas Universi^ Bui. 135, Sc ser. No. 14: 7-8, 1909. 93 94 Diseases of Greenhouse Crops b. Colored areas or spots. White or gray, such as mildews, white rusts, etc. Yellow, many leaf spots. Red or orange, rusts, leaf spots. Brown, many leaf spots. Black, black rusts. Variegated, leaf spots, mosaic 2. Shot hole, perforation of leaves. 3. PF27ft«^, wilts, damping off. 4. Necrosis, death of parts such as leaves, twigs, stems, etc. 5. Atrophy, dwarfing or reduction in size. 6. Malformations or excrescences, galls, pus- tules, tumors, "cankers, rosettes. 7. Exudation, slime or gum flow. 8. Rotting, dry or soft rots. 1. Diseases of a Mechaxical Nature Greenhouse plants, contrary to those grown out- doors, are open to but few injuries of a mechanical nature, for it is seldom, indeed, that indoor plants are injured by rain, hail, or frost. Sunburn. While most greenhouse crops require a great deal of light, a few are injured by it. Some varieties of tomatoes, the Earliana especially, tmder the influence of strong sunlight are subject to sun- scald. Sunburn may be overcome by shading the glass. Of the various shading materials, the cheap- est and quickest to use is air-slaked lime. The Nature of Plant Diseases 95 most expedient to use is air-slaked lime which has been slaked dry by sprinkling lightly with water. This is diluted in water and applied as a spray. If new lime is used it will be more difficult to wash off later. Moreover, it seems that air-slaked lime sticks a good while, but rubs off easily. It is far more desirable to use shading material that must be applied twice in the summer than something that will stick hard and remain during the fall and win- ter season. Smoke injury. As a rule large greenhouse estab- lishments are situated near large cities which are centers of industrial production and manufacture. Greenhouse plants are often injured from the effect of smoke or gases which escape fr6m the furnaces into the air. The sources of smoke may be classified into three divisions: (i) Smoke from large buildings or from manufacturing plants; (2) Smoke from locomo- tives; (3) Smoke from chimneys of dwelling houses. Smoke is generally produced because of improper furnace construction, such as improper draft, over- loaded boiler, insufficient air space, insufficient air supply to boiler room, and also by carelessness qf operation. Smoke contains large quantities of carbon dioxide, steam and sulphur dioxide, besides its characteristic soot. The latter consists of carbon, tar, and mineral matter mixed with small quantities of sulphur, arsenic and nitrogen compounds which are of an acid nature. Soot adheres to plants, especially to 96 Diseases of Greenhouse Crops foliage, giving them a burned, contorted appearance. Another effect of soot and smoke is to close up the stomata or respiratory openings of the leaf, so that asphyxiation results. The effect of smoke on plants is a loss of leaflets in case of compound leaves, and an abnormal curling and distortion. Lesions and spots may be formed on the foliage as a result of the sulphur dioxide which is present in smoke. The spots are at first small, but soon enlarge and finally involve the whole leaf, which dries and becomes gray. Smoke injury, although of a mechanical na- ture, may also be considered from a physiolo^cal point of view. The after effect of smoke on plants resolves itself into a question of insufficient food supply and assimilation. This is indirectly brought about by diminished illumination, interference with the normal transpiration and the reduction of leaf surface. Methods of Control. There is as yet no definite method of control known, consequently all that can be done is to avoid the smoke belts. The greatest injury usually occurs in locations to the leaward of smoky districts and when the soil is wet. As far as possible, therefore, postpone irrigation during the windy days. 2. Physiological Diseases In this class are included disturbances which are due to unfavorable conditions of nutrition. There are numerous diseases of plants which are brought Nature of Plant Diseases 97 about by lack of, or by an excess of, certain food elements in the soil. The effect is an interference with the proper life functions of plants. Malnutrition Symptoms. The symptoms of malnutrition are not always the same. They differ somewhat with the crop, the nature of the soil, and the fertilizer applied. In malnutrition the symptoms to be looked for are retarded growth, change of color in the foli- age and root injury. Affected plants remain dwarfed at a time when maximum growth is ex- pected. The color of the foliage turns a lighter green, especially in the spaces between the veins, which become yellowish green to brown. Roots of such plants are poorly developed, and secondary roots are often missing. Causes of Malnutrition. The work of Stone*, and Harter f and others seems to have established the fact that malnutrition cannot be attributed to the work of parasitic organisms. Stone cites in- stances where constant watering with liquid fertil- izers or manure would cause malnutrition in cucum- ber plants. The same is also induced when pig and cow manure are mixed, or when manure is worked into a soil already well fertilized otherwise. Harter records cases of malnutrition brought about by an 'Stone, G. £, Massachusetts Agr. Expt. Sta., Ann. Rept, 5-13: 1910. t Harter, L. L., Virginia Truck Expt Sta., Bui. i : 4-i£, 1909 (Norfolk, Va.). 98 Diseases of Greenhouse Crops excess of acidity in the soil. In soils where plants suflFer from malnutrition, from 3,500 to 6,000 pounds of lime per acre area are often required to neutralize the excess of the soil acidity. This con- dition is apparently the result of intensive trucking and the heavy application of chemical fertilizers which leave the soil acid. Sulphate of ammonia, muriate and sulphate of potash and acid phosphate when used continuously will leave the soil in a very acid condition. On the other hand, nitrate of soda, carbonate of potash and Thomas phosphate tend to make the soil alkaline. Another important cause of malnutrition is the exhaustion of humus. This is a natural result where commercial fertilizers are used instead of some form of organic manure. Methods of Controlling Malnutrition. It is quite obvious from what has already been said, that the greenhouse grower is the loser if he uses his fertilizer injudiciously. Not only is malnutrition favored by such a course, but the yields, too, are considerably re- duced. With acid soils, liming to neutralize the soil acidity will help control malnutrition. Chlorosis This disease may be attributed to several causes. Greenhouse plants that receive too much shade will become yellowish, then whitish, and in time may lose all their green color and finally die. Chlorosis is often brought about when plants grow in soils Nature of Plant Diseases 99 that have become too alkaline. This is true for soils containing an excess of lime, wood ashes, or magnesia, and especially when nitrate of soda is used in excess. Control. Chlorosis when brought about by the lack of available iron in the soil may be remedied by the application of small quantities of iron sul- phate. If the disease is caused by the other factors previously mentioned, a cure may be effected by re- moving tiie cause. Blossom Drop This is another trouble which may be termed physiological and the cause of which carmot be at- tributed to the work of parasitic organisms. It is often noticed on tomatoes and various other plants. Various causes lead to it. Sudden drops of tempera- ture at blossoming will induce many plants to shed their blossoms. Blossom drop may also be brought about when too much nitrogen is applied to the soil in the form of manure, especially hen manure. To overcome this, the fertilizer in the soil must be bal- anced by the addition of 600 pounds of acid phos- phate and 150 pounds of muriate of potash per acre. Overacidity in the soil may also cause the shedding of blossoms. A sudden checking of the water sup- ply, or overwatering may have the same effect. Finally, improper pollination is often one of the main causes for the blossom drop of greenhouse plants. In the field, |}ollination is favored by both 100 Diseases of Greenhouse Crops wind and insects. In the greenhouse, these two agencies are practically shut out. With forced cu- cumbers, the difficulty is often overcome by install- ing beehives in the house. Bees are very active imder high temperature conditions, and perfect pol- lination is the result. The usual practice is to sup- ply a beehive to every 200 feet of house. The hives should be placed on platforms several feet above the bed to protect the bees from becoming drenched during the watering or sprinkling of the beds. We should bear in mind that the hives must be taken out whenever the house is fumigated with potassium cyanide. Nicotine fumes do not seem to injure the bees, especially if the fumigation is carried on at night. Bees may be used to pollinate practically every crop grown in the forcing house. It seems, however, that bees refuse to work on to- matoes, perhaps because of a dislike for their nec- tar. In this case, then, it is necessary to pollinate by hand. The investigations of Fletcher and Gregg* and others have shown that the setting of a good crop of smooth heavy tomatoes depends largely on the proper distribution of pollen over the stigma. A lack of pollination will of course result in no crop. An uneven distribution of pollen will result in too large or irregular fruit. During the winter and on sunny days, it will pay to go over the plants and tap each blossom with the finger or with a stick on which is fastened a small glass rod or spoon. This •Fletcher, S. W., and Gregg, O. T., Michigan Agr. Expt Sta., Special Bui. 39: z-io, 1907. Nature of Plant Diseases loi will shake out the pollen and enough of it will be liberated by this operation to insure complete fertili- zation. A high temperature will favor the maturing and the bursting of the pollen sacs even during cloudy weather. It is, therefore, advisable to run up the temperature of the house as high as is ex- pedient on the days when the tapping of the blos- soms is done. This should always be done during the day and never at night. The pollen sacks (an- thers or male organs) do not burst freely until after the yellow petals have fully expanded and have begun to wither slightly. The pollen is discharged most freely in a hot dry atmosphere. 3. Diseases Brought About by Parasitic Flowering Pjlants or Micro-organisms In this class of diseases may be mentioned those which are induced by parasitic flowering plants such as the dodder and the broom rape. These, however, as well as the diseases induced by bacteria and fungi, will be considered under their respective hosts. Carriers of Diseases. In the greenhouse, dis- ease producing organisms are often brought directly with infected soil or manure in the compost. Fusa- rium lycopersici Sacc, the cause of sleeping sickness of tomato, as well as large numbers of other para- sites, are brought in that way. Little as yet do we realize the importance of in- sects as carriers and disseminators of plant diseases, although we are becoming increasingly aware of 102 Diseases of Greenhouse Crops their role in human and animal pathology. Acting as carriers of spores of parasitic fungi, which may adhere to any part of their body, they are responsible for distributing plant diseases. Insects, too, by feed- ing on plants or in searching for the nectar of the blossoms, are likely to come in contact with diseased parts. Their bodies may become coated with spores of parasitic bacteria or fungi, which are thus car- ried from plant to plant and from field to field. The striped cucumber beetle is known to carry the virus of cucumber mosaic, and the germ of cucumber wilt (Bacillus tracheiphillus Ew. Sm.). It is there- fore very essential that every effort should be made to keep insect pests out of the greenhouse. 4. Diseases of Unknown Origin Mosaic In this class will be included those diseases which spread by contact, but the exact cause of which is unknown. Special emphasis will be given to that important disease known as mosaici This trouble attacks a variety of greenhouse plants. It is especially severe on the tomato, cucumber, and sweet pea. Symptoms. Mosaic is readily distinguishable by a yellow dotting or mottling on the foliage, present- ing in some instances a beautiful mosaic structure, whence its name. Affected leaves linger and often curl. Nature of Plant Diseases 103 Cause of Mosaic. The cause of Mosaic is as yet a disputed question.* AUard claims that mosaic is caused by an ultra-microscopic pathogen, that is, a parasitic organism which cannot be detected by our present technic in microscopy. Mosaic may be transmitted from plant to plant. The easiest way to prove this is to rub with the fingers a diseased leaf and then immediately rub a healthy one. The disease will appear on the inoculated host in about ten days. In the greenhouse, the green aphid and the white fly act as carriers of mosaic. Control. Methods of control in mosaic lie in the direction of prevention. Diseased plants should be destroyed by fire, and all indoor insect pests kept in check. * See also Taubenhaus, J. J., Truck Crop Diseases, E. P. Dutton Co, 1918, New York, N. Y. CHAPTER 8 GERMINATION TROUBLES Diseased Seed. Numerous failures in geraiina- tion may be directly attributed to diseased seed. These may cany infection internally in the form of mycelia in the invaded tissue. Seed may also carry infection material externally in the form of spores or sclerotia adhering to the seed coat. Age of Seed. In determining the cause of poor germination, the age of the seed is to be considered, for after a certain age limit deterioration sets in. Each kind of seed has its own age limit, which is generally determined by the character of the seed itself, i.e., whether oily or starchy, or lacking in both. Thus the vitality of the minute seed of tobacco is perhaps eight times as great as that of the large oily seed of the castor bean. With many species of seed there are apparently no external symptrans to indi- cate loss of vitality due to age. Cultural Conditions. The viability of seed is also largely determined by the conditions undei which the previous crop grew. The more vigorous the mother plant the more vitality will there be impart- ed to its offspring. The vigor of the previous crop depends on favorable climatic conditions, care in 104 Germination Troubles 105 cultivation, and in fertilization. Old seed produced in a favorable season may be preferred to fresh seed of an inferior quality produced in a bad season. Weight and Color of Seed. As a rule, light weight seed is inferior to heavy seed of the same variety. The weight of the seed is influenced by culture, and by imperfect fertilization which results in minute and weak embryos. The cwnparative weight of seed may be readily determined by the water method. Place the seed in a tumbler filled with water. After shaking and letting it stand for a few minutes, the heavier seed sink and the lighter float. Using this method, Stone * has shown that the heavier sinking seed give a higher percentage of germina- tion than the lighter. (See Table 15.) Table 15 Name of Seed) No. vf Seed Germinated Per Cent, of Increase in Germination ofHeavyOver LigUSeed Light Heaoy Lettuce 68 100 38 44 50 60 90 85 88 58 87 32 Onion 17 Onion 142 Lettuce 100 17 Average 61 The color of the seed does not seem to have any influence on the germination. Darker colored seed is usually preferred to the lighter of the same va- riety. Color, however, largely depends on the de- gree of ripeness. •Stone, G. £., Massachusetts Agr. Expt Sta., Bui. 121 : 3-14, 1908. io6 Diseases of Greenhouse Ci;ops Storage Conditions. The vitality of seed is great- ly influenced by storage conditions. The longest lived seed may be ruined by improper storage. The ideal conditions of storage, however, are not always those which "favor germination. Seed should be cured or dried before storing. The drier it is the less likely it is to spoil and the higher will be the temperature that it can stand. When large quanti- ties of seed are to be handled by the trucker, it is advisable to build a seed house. The seeds are best kept in strong paper or cloth bags, placed in tin or galvanized iron cans. Seed Testing. In buying seed we must never take it for granted that the germination will be per- fect. To make sure, a sample of the seed should be tested for germination. The simplest method, per- haps, is to sow a definite number of seed in a shal- low pan filled with moist sand, and kept covered in a warm, dark place. However, the fact that a seed sprouts does not always imply that it will develop into a normal plant. Hence, allowance should be made for this probability when making a test at home or in the seed laboratory. Effect of Fertilizer on Seed. With the hope of hastening germination, greenhouse men often apply various fertilizers to the seed bed. This practice cannot be too strongly discouraged, especially when muriate of potash and nitrate of soda are used. These two fertilizers when used in strengths of one per cent, or more, inhibit the germination of the seed, whether applied directly or mixed with the Germination Troubles 107 soil. Phosphoric acid or lime, when not used in excess, seems to have no injurious action on seed germination. However, on no account should com- mercial fertilizers be brought into direct contact with the seed. This is well brought out in Table 16 by Hicks.* Table 16 Effect of Chemical Fertilizers on the Germination of Breakfast Radish Seed Fertiliser Used How Applied First Sprouts Per Cent, of Germi- nation Potash Phosphoric Acid Nitrogen Lime Mixed Fertilizer Check, no fertilizer. In the rows Mixed with soil. In the rows. . . . Mixed with soil. In the rows Mixed with soil. In the rows. ... Mixed with soil. In the rows Mixed with soil. No sprouts No sprouts May 26 May 24 May 25 May 26 May 24 May 24 May 25 May 24 May 24 1.5 1-5 lO.O 950 2.0 6.5 37-5 930 34-5 92.0 96- 5 Seed Treatment. Since seed is often a carrier of disease it is essential that it be treated before plant- ing. Treating the seed for about ten minutes with sulphuric acid will hasten germination and destroy adhering spores of disease-producing organisms. However, more information is needed before this method can be universally adopted by the green- house grower. In practice, the safest method would be to soak all seed, before planting, in a solution •Hicks, G. H., U. S. Dept. of Agr., Div. of Botany, Bui. 24: 5-15. 1900. io8 Diseases of Greenhouse Crops of one part of formaldehyde in 320 parts of water, i.e., one pint of formaldehyde in 22 gallons of water. The soaking is carried on for 10 or 20 minutes, depending on the size of the seed and per- meability of the seed coat. CHAPTER 9 DISEASES OF GREENHOUSE CROPS Asparagus {Asparagus Officinalis) Cultural Considerations. Asparagus plants lend themselves admirably to forcing. It is now grown for commercial purposes on a fairly large scale in- doors. Light is not essential for this crop. The beds may be in total darkness, although a diffused light is preferred. Any variety which produces large shoots is desirable for forcing. However, the variety Reading Giant has been developed for its resistance to rust, and therefore should be given pref- erence. Forced asparagus may be grown in any soil, even sand or coal ashes, provided it contains plenty of organic matter. At the beginning of the forcing process, the temperature should not run higher than 45 to 50 degrees F. for at least one week. As soon as strong shoots are made, a temperature of 65 to 70 degrees is desired. In order to obtain high yields, profuse watering is necessary. Diseases of Asparagus Greenhouse asparagus seem to be subject to but few diseases. Damping Off, see Rhizoctonia, p. 20. 109 no Diseases of Greenhouse Crops Rust (Puccinia aspargi D.C.) seems to be of no unportance as a disease of forced asparagus. Bean (Phaseolus Vulgaris^ Cultural Considerations. Beans are not to be grown as a fall or winter crop. They are produced more easily and more profitably as a spring crop. In this case they follow well a winter crop of let- tuce. The night temperature should not go below 60 degrees F, The best soil for bean culture is a rich light sandy loam. The soil should never be al- lowed to become damp and cold for any length of time. It must not be allowed to become packed and soggy through overwatering. As a safe guide to succesSj the crop should never receive a check in its growth in any period of its development. Of the varieties adapted to forcing may be mentioned, Black Valentine, Long Yellow Six Weeks, Ken- tucky Wonder. Diseases of the Bean Forced beans may be attacked by several impor- tant diseases. Blight Caused by Fseudomonas phaseoli Ew. Sm. Symptoms. If the soil is too wet during planting time, the seed may rot in the ground and never ger- minate. At other times the roots of the young seed- lainmcitau coiMi AnThraoioK 5porti t CufAtnus . .<■' Starch Grams Fig. 15. Bean Diseases. a. Anthracnose on pods (after Halsted), b. cross section of bean seed to show relationship of Colletotrichum lindemuthianum to its host, c. cross section of bean seed to show canker produced from anthracnose (b-c after Whetzel), d. cross section of bean tissue to show presence of the bean blight organism, e, Pseudomonas phaseoH {d-e after Smith, £. F.)< Bean Diseases iii lings may decay and the result will be a very poor and uneven stand. Under drier ccmditions a better germination is obtained. The disease also works on the older plants, forming irregular spots. When their root system is attacked, affected plants becrane yellowed and wilted by daytime, but slowly revive at night. Should the air become mu^y by over- watering and high temperatures, infected plants ap- pear as though they have been drenched with hot grease, the leaves having a burned appearance. The injured plants then seem to make a desperate at- tempt to produce new foliage, which in turn becomes affected; the pods cease filling, and ripening is very uneven. In carefully examining diseased seed, it is found to be yellowed and shriveled; or, in light cases of attack, covered with irregular yellow blotdies. On the leaves, the trouble appears as watersoaked spots which later becrane amber colored. The cankers on the stems scMnewhat resemble the canker produced by Colletotrichum lindemuthianum. The Organism. Pseudomonas phaseoli Ew. Sm. is a short rod, rounded at both ends, and motile by means of polar flagella (fig. 15, d and e.). It lique- fies gelatin slowly, coagulates milk, and produces no gas. For methods of control, see Anthracnose, p. 112. SCLEROTINIA RoT Caused by Sderotinia libertiana Fckl. Sclerotinia rot is a disease which attacks snap 112 Diseases of Greenhouse Crops beans. During a period of several hot humid days the disease may suddenly break out in great se- verity. Usually withering and decaying of stems and pods where the plants are thickest is the first S3Tnptom that attracts attention. On closely ex- amining infected stems and pods, we find that they are watersoaked, and overrun by a white mycelial growth on which appear numerous hard, black scle- rotia. In the field, the Black Valentine snap bean seems to be more resistant to rot. For a description of the causal fungus and methods of control, see let- tuce drop, p. 150. Powdery Mildew Caused by Erysiphe polygoni D. C. Symptoms. Powdery mildew is a serious bean disease. It is characterized by white, mealy patches on the surface of the leaves and stems. The foliage soon turns yellow and dry. Powdery mildew may be controlled by dusting the plants with flowers of sulphur. Care in the proper amount of watering and ventilation will also help to keep it in check. Anthracnose Caused by Colletotrichum lindemuthianum (Sacc. & Magn.) B. and C. Symptoms. Anthracnose is so characteristic that it cannot be mistaken for any other disease, except perhaps the blight. In light attacks, the seeds are Bean Diseases 113 covered with sunken brown to black specks. These are especially evident on the white seeded varieties. In severe attacks, the seeds are covered with deep sunken black spots (fig. 15, c.) which are rifted in the center. On the leaves the disease attacks the veins, which become blackened and somewhat shrunken. Frequently it attacks the petioles, espe- cially at the point of leaf attachment. In this case, the foliage drops off, leaving the bare petioles or stems. Anthracnose on the pods begins as small, circular, pin-point, dark red spots which enlarge, and later elongate into maroon colored pits, cracks, or cankers (fig. 15, a.). On young seedlings the stem rots off a short distance above ground. The Organism. Spores are formed on the spots or cankers of all parts affected (fig. 15, b.). These are imbedded in a gelatinous substance and may be- come loosened only by water splashing upon it. It is at this stage that the disease becomes serious, for it is then spread from plant to plant. When the spores are lodged on a new bean plant or on a new part of the same plant, infection takes place through the penetration of the tube of the germinated spores. Control. Spraying has not given satisfactory re- sults. The best control is to plant clean seed select- ed from clean pods. The latter, before shelling, may be dipped for ten minutes in a solution of one part of corrosive sublimate to a thousand of water. The treated pods are then dried in the sun, shelled, and the seed put away in dry Mason jars until planting time. Should weevils threaten these seeds, they 114 Diseases of Greenhouse Crops may be fumigated with carbon bisulphide. Under no circumstances should infected plants be syringed. When this is done the spores of the fungus are scat- tered broadcast. Recently Burkholder * has suc- ceeded in developing a resistant bean by crossing the Well's Kindney Bean with the White Marrow va- riety. Root Rot, see Rhizoctonia, p. 20. Root Knot, see Nematode, p. 28. Beet (Beta vulgaris'^^ Cultural Considerations. Beets are not grown very extensively in the greenhouse. They are, how- ever, raised on a small scale for greens or for the roots. It is often used as a companion crop with tomatoes. The Egyptian or any other early variety is preferable. The cultural requirements of the beet are the same as those of the lettuce, see p. 145. However, beets will grow more rapidly under higher temperatures than lettuce. Diseases of the Beet Indoor beets are subject to less diseases than those grown out of doors. The following are the more important ones: Crown Gall Caused by Fseudomonas tumefaciens Sm. and Town. 'Burkholder, W. H., Pbytopath. 8: 353-359, 1918. Fig. i6. Beet Diseases. a. Nematode or root knot, b. Crown gall, t. Cercospora leaf spot (after Halsted), d. spores of Cercospora beticola (after Scbwarze). Beet Diseases 115 Crown gall is a very important disease because of its cosnu^litan nature, for it is widely prevalent and attacks a lai^ number of hosts. Symptoms. The disease does not usually mani- fest itself until the roots are nearly half grown. Abnormal outgrowths or galls (fig. 16, b.) appear which vary in size from that of a garden pea to nearly two inches in diameter, according to the se- verity of the attack. The galls are usually attached to the beet by a narrow string. In light cases of infecticm there may be but one gall cm the rootj in severe cases, however, the roots may be covered with niunerous galls. TTie Organism. The cause of crown gall is a bac- terial organism, Fseudomonas tumefaciens Sm. and Town. It is a short rod, multiplying by fissicm, and moves about by means of poldt flagella. On agar or gelatin it forms small round white colcmies. Un- der unfavorable c«iditi(Mis it readily develops in- volution forms; the organism is short lived in pure culture. P. tumefaciens lives over in the soil frtxn year to year. Control. The disease may be introduced with in- fected soil. Sterilizing the soil with steam or for- maldehyde (see pp. 32-43) is reccmmended. Scab Caused by Actinomyces chromogenus Gasp. Scab on beets is the same as the scab of the Irish potato, the radish, and the carrot. ii6 Diseases of Greenhouse Crops Symptoms. The symptoms of the disease on beets do not differ from those of the Irish potato. Occa- sionally, the scabs which arise before the beet is full grown disappear entirely, leaving merely a small scar. This is somewhat sunken and has a definite outline. In normal cases of infection, the scabby areas on the beet are rough; while the corky layer of the spots decidedly bulge out. Immediate- ly below them, the tissue is a discolored reddish brown. The Organism. The cause of beet scab is the same as that of the scab of the white potato. The parasite is a soil organism, and thrives best under alkaline conditions. Control. The disease is introduced with infected soil, or with the compost. Care should be taken that no infected potato peelings find their way to the manure pile. Soil sterilization with steam, or formaldehyde (see pp. 32-43) is recommended. Damping Off and Root Rot Caused by Pythium de Baryanum Hess. Symptoms. Damping off very commonly occurs just as the seedlings emerge from the ground. These topple over and die in the characteristic way so fa- miliar to truckers. The greatest damage follows from overwaterings, when a hard crust is formed on the surface, a condition which prevents the seedlings from emerging normally. On old and mature roots, Pythium de Baryanum may cause a rot. A pecu- Beet Diseases 117 liarity of this disease is that it seldom starts at the top of the crown. The latter appears to be perfectly healthy, although the leaves turn yellow, indicating a diseased condition further down. Rotted roots are found to be overrun by a varied flora, although Pythium is the original cause of the trouble. For a further description of the organism see p. 17. Control. The methods of controlling this dis- ease are the same as those for lettuce drop, see p. 151. Downy Mildew Caused by Feronospora scJiachtii Fckl. This disease is of little economic importance in the United States. The trouble, however, is preva- lent in Europe. The mildew attacks the young seed- lings in grayish patches on the under side of the foliage. On older plants, the mycelium of the causa- tive fungus works downwards into the root, causing it to rot. Drop Caused by Sclerotinia lihertiana Fckl. Drop, which attacks young seedlings of the beet, but not the older plants, is not very different from a similar trouble on lettuce. The high temperature of the soil soon after making the hot bed, is important in favoring the disease. Sterilizing the soil with formaldehyde, careful regulation of temperature, and watering are methods to be observed in the con- trol of the trouble. Ii8 Diseases of Greenhouse Crops Leaf Spot Caused by Cercospora beticola Sacc. There is perhaps no beet disease that is of greater economic importance than leaf spot. The trouble is well known to truckers and it seems to be found wherever beets thrive. Symptoms. The disease first makes its appear- ance on the leaves as tiny circular whitish spots. These gradually increase in size and assume a brown- ish color. The spots soon multiply and involve the entire leaf area (fig. 16, c), which becomes dry and brittle. Leaf spot attacks the outer and older leaves first. As the inner foliage advances in age, they too become infected in turn. Serious though the dis- ease may appear, it never kills the plant. The re- sult, however, is noticeable on the roots, which are undersized and elongated instead of round. Leaf spot generally appears in overwatered and poorly ventilated houses. The disease increases in severity as the plants are weakened by heat. The Organism. The fungus, Cercospora beticola^ Sacc, like most fungi, is composed of a vegetative part of mycelium and of spores. The latter are microscopic in size, somewhat needle-shaped, and di- vided by means of a cross wall into cells numbering from two to seven (fig. 16, d.). Each of these cells may germinate by sending out a thread-like tube, which penetrates the leaves through the stomata. The spores are borne on a cluster of stalks or conidio- phores, at the base of which is formed a small Beet Diseases 119 stroma. The temperature and relative humidity of the air influence the production and infection of conidia. Conidia are generally formed on the lower surface of the leaves, no doubt because these are subject to a higher humidity. Control. Infected material should be destroyed by fire. Spraying with Bordeaux mixture 4-4-50 is also recommended. Root Rot Caused by Rhizoctonia solani Kuhn. Symptoms. This disease produces a damping off of the young seedlings, and on older plants a rotting of the crown. Upon pulling out an infected plant, we find that the outer leaves are dead and dry, while the inner ones are somewhat curled. The roots of such plants invariably are rotted at the crown, the rot generally working inwards to a considerable ex- tent. The peculiarity of this disease is that the lower half of the root is generally sound. Frequent- ly, the rotted crowns are also found to be cracked at various places. Beets thus affected are worthless for the market. For a description of the fungus see p. 20. Control. There are no methods of control known. The factors which favor the trouble are poor drain- age, an excess of soil moisture, and lack of suffi- cient ventilation. Every step taken to overcome these will in a degree help to control the rot. Soil sterilization is also recommended. Root Knot, see Nematode, p. 28 (fig. 16, a.). 120 Diseases of Greenhouse Crops The organisms Pseudomonas teutlium Met., Pj. heticola Ew. Sm., Urophlyctis leproides (P. Mag.) Trab., Cystopus bliti (Biv.) Lev., Uromyces beta. Kuhn, and Phoma beta Fr. seem to attack beets out of doors only. Carrot (Daucus carota) Cultural Considerations. Carrots are forced in about the same way as the radish. The soil, how- ever, should be more sandy. The variety best adapt- ed for forcing is the early small topped Short Horn type. Diseases of Carrots Carrots are very hardy and subject to but few diseases of consequence. Soft Rot, see Cauliflower, p. 126. Root Rot, see Rhizoctonia, p. 20. Cauliflower {Brassica oleracea var. botrytis") Cultural Considerations. Cauliflower is not so extensively forced because large amounts of it are shipped from California during the forcing season. Nevertheless, indoor cauliflower is far superior in quality, and with the proper advertisement the forced product should gain greater recognition frcMn the consumer. There are few varieties which lend themselves well to forcing. The Snowball and the Erfurt are preferred by most growers. The soil Carrot Diseases 12 1 should not be too heavy, although the plants are heavy feeders. The compost should contain a fair amount of well rotted manure. In addition, a well balanced fertilizer may be added at the rate of 1,000 pounds per acre. Lime should also be added to the beds at least once every two years. This will sweeten the soil in case it has a tendency to sour. Cauliflower requires an abundance of water. Lack of sufficient water may check the growth, an eflfect that will result in small or no heads. On the other hand, overwatering may produce an excess of foliage at the expense of head development. In warm weather, the plants and the walks should be syringed in order to keep the atmosphere moist. The best night temperature is about 50 to ^^ degrees F. and the day temperature from 65 to 70 degrees. Plenty of ventilation should be provided; but drafts should be avoided. CHAPTER lo DISEASES OF CAULIFLOWER Indoor cauliflower seems to be subject to less dis- eases than that grown out of doors. The troubles which attack this plant are practically the same as those which are found on the cabbage. Club Root Caused by Flasmodiopkora hrassica Won Symptoms. Affected plants show a wilting of the foliage in the day, although recovering in the eve- ning or during cloudy weather. Diseased plants are dwarfed, pale, and sickly looking. The seat of the trouble is at the roots. The latter swell considerably in size, often taking on the form of a hernia (fig. 17, a-c). The disease is more severe on seedlings in the seed bed, from whence it is carried to the field or to the greenhouse. The Organism. Club root is caused by a slime mold. The spores of the parasite (fig. 17, d.) are nearly round and possess a transparent and refrac- tive cell wall. The first signs of germination are a swelling of the spores, followed later by a bulging at one side. The inner pressure exerted splits the spore wall, thus permitting the protoplasm (swarm 123 Fig. 17. Cauliflower Diseases. a, Youn^ cauliflower plant with club root (after Jones, L. R.). &• cross section of an infected root, c. cross section of a young healthy root (b-c after Woronin), d. host cell containing Myxomycete spores (after Lutman, B. F.). Cauliflower Diseases 123 spores) to ooze out. The latter is without a cell wall, and moves by means of a thick flagellum at the small end. The germination of the spores is im- proved by exposing them for a short time to cold and drying. The best medium is water which has been filtered through muck soil. Infection of the hosts takes place through the wall of the root hair while the organism is in a uni- nucleate stage. Entrance of the parasite is evi- denced by the browning and shriveling of the root hair. Control. If this disease becomes introduced into the greenhouse, the safest course would be to ster- ilize the soil in the benches and in the seed bed. Sterilization with steam or formaldehyde is recom- mended (see pp. 32-43). Bacterial Leaf Spot Caused by Pseudomonas maculicolum McC. Symptoms. The disease is characterized by nu- merous small brownish to purple-gray spots. When the small spots coalesce, the entire leaf surface may be involved. Practically all parts of the leaves are affected. When the midribs and veins are attacked, the tissue becomes shrunken, and the leaves have a puckered appearance. In the early stages of infec- tion, the spots on the leaves are watersoaked, later they become dry and turn dark merging into pur- plish gray. In transmitted light, the centers of the spots are thin, almost colorless, and are surrounded 124 Diseases of Greenhouse Crops by a dark border. The diseased leaves become yel- low and drop oS prematurely. The trouble appar- ently does not attack the cauliflower head. The same disease may also attack the radish. The Organism. The disease is produced by Pseu- domonas macuUcolum, a rod-shaped organism, with rounded ends, usually forming long chains in cer- tain media, but producing no spores. The organism is actively motile by means of polar flagella. Invo- lution forms are produced in alkaline beef bouillon; and pseudo-zoogloese occur in acid beef bouillon. No gas is produced and the organism is aerobic. It is killed by drying and exposure to light. Control. Badly diseased plants should be pulled up and destroyed. Spraying with 4-4-50 Bordeaux is recommended. In spraying cauliflower with cop- per compounds, and especially if the latter are in a concentration somewhat stronger than the plant can stand, nimierous warts will appear on the leaves in about three days after spraying. These warts should not be mistaken for a disease induced by a parasitic organism. The wart formation is apparently due to a stimulation from the salts absorbed by the host cells. Black Rot Caused by Fseudomonas campestris (Pammel) Ew. Sm. The disease is known both as stem rot and black rot. The latter perhaps is the more common name. Symptoms. Black rot has distinct symptoms Cauliflower Diseases 125 which cannot easily be confused with other diseases. On the leaves, the symptoms are manifested as a burning appearance on the edges and a yellowing of all the aflFected parts except the veins, which re- main blackened. Frcxn the margin of the leaves, the disease works downwards to the stalk. Frcttn there it travels up again to the stems and leaves. The parasite works in the fibrovascular bundles of the leaves and main stalk, causing a premature defoli- ation. Occasionally, the disease enters one side of the stalk, the latter beccwning dwarfed and the cauli- flower head grows one-sided. In severe cases of attack, there is a total lack of head formation. Upon splitting open a stump of an affected plant, one finds a black ring which corresponds to the places of the fibrovascular bundles invaded by the organism. In- fection takes place through small openings naturally found on the leaves and known as water pores which are scattered over the teeth of the leaves. Infec- tion by means of insect bites is also a very cranmon occurrence. Outbreaks of black rot may undoubt- edly be traced back to the use of infected manure. Black rot also attacks greenhouse radish. The Organism. Pseudomonas campestris is a rod- shaped organism, slightly longer than it is broad. When young it is actively motile by means of long polar flagella. It is found single or in pairs and produces no spores. It liquefies gelatine completely in about Kteen days. On agar plates the colonies are round, yellow in color, and the margin entire. 126 Diseases of Greenhouse Crops On potatoes a liberal growth is produced with no odor and no browning of substance. Control. Before planting, cauliflower seed should be disinfected for fifteen minutes in a solution of ^ pint of pure (40%) formaldehyde diluted in seven gallons of water. In making the seed bed, manure known to be free from cabbage refuse should be used. All insect pests should be kept in check by spraying with arsenate of lead. The disease can- not be controlled by merely cutting off diseased foliage. If anything, this operation aggravates the trouble. Diseased plants should be pulled out and destroyed. Soft Rot Caused by Bacillus caratovorus Jones. Soft rot, although a field trouble, causes consid- erable damage to greenhouse cauliflower. Symptoms. The disease is characterized by a soft, mushy to slimy decay of the entire plant. The dis- ease works very rapidly under favorable conditions of moisture and temperature. The causal organism can gain entrance only through a wound or bruise. The Organism. Soft Rot is caused by a bacillus that is rod-shaped, of varying length, and usually formed in chains. It moves about by peritrichous flagella. It completely liquefies gelatine in about six days. Gas is produced with a majority of str^ns. Control. Diseased plants should be destroyed by fire. To check further spread, water should be with- held and plenty of ventilation allowed. During Cauliflower Diseases 127 watering unnecessary splashing of soil particles on the plants should be avoided. Damping Off Caused by Olpidium brassica (Worr.) Dang. The symptoms of damping off for cauliflower are similar to those produced by Pythium de Baryanum, p. 17. The sporangia of the parasite may be found singly or in groups in each infected host cell. The zoospores are globose, uniciliate. The resting spores are globose, wrinkled, and star-like in appearance. The disease is found mostly in seed beds, where it does considerable damage. For methods of con- trol, see pp. 32-34. Downy Mildew Caused by Peronospora parasitica (Pers.) De By. Symptoms. Downy mildew, while a common field disease, causes considerable damage to young seed- lings in the seed beds. It is characterized by whit- ish downy patches on the underside of the leaf. Seen from above, the affected areas are angular, pale yel- low, and somewhat shrunken. The spots seem to be limited by the veins of the leaves. The disease is common in damp houses. Besides the cauliflower, the radish, and numerous other cruciferous hosts are known to be susceptible to downy mildew. The Organism. The sporophores of the fungus are stout and numerously branched, each of these re- peatedly forked. The tips of the smaller branches 128 Diseases of Greenhouse Crops are slender and curved. The conidia are broadly elliptical, and the resting spores are globose and smooth, becoming wrinkled with age. Control. In the seed bed, spraying with 4-4-50 Bordeaux will control the disease. The first applica- tion should be given as soon as the disease makes its appearance. Later the application will be governed by disease conditions. Care should also be taken to avoid sowing the seeds too thickly. Overwater- ing, poor ventilation, and high temperature favor the disease. Drop Caused by Sderotinia libertiana Fckl. Drop is a disease fairly common on cauliflower. The trouble may be recognized by a drooping and wilting of the leaves. The bases of the affected foliage are covered with a white weft of mycelial growth, later by sclerotia. For a more extended discussion of the disease, see lettuce drop, p. 150. Ring Spot Caused by Mycosphterella brassicacola (Duby) Lind. Symptoms. On the leaves, the disease appears as numerous small spots and the affected foliage turns yellow. Most of the spots are formed on the laminffi, but others are also formed on the large midribs. The spots are definite in outline, round Cauliflower Diseases 129 and visible on both surfaces of the leaf. The color is light brown to gray, with dry centers surrounded by olive green or blue green borders which shade off into the natural color of the leaf. The outer edge of the spot is covered with the fruit of the fungus. Spraying with 4-4-50 Bordeaux is recommended. Black Mold Caused by Alternaria brassier (Berk.) Sacc. Affected leaves are covered with spots which are nearly black on the under side of the leaf. The spots are composed of a series of rings, the smaller ones enclosed within the larger. There is no distinct border separating the diseased portions from the healthy; the spots gradually shade off into the healthy tissue. Little is known of the causative fungus or of the control of this disease. It is prob- able that spraying with 4-4-50 Bordeaux will be of value. Root Knot Caused by Heterodera radicicola (Greef) Mull. Root knot is characterized by small swellings on the lateral feeding roots. For a description of the parasite and methods of control, see p. 28. Celery (^Apium graveolens) Cultural Considerations. Celery has not yet taken its place among the standard forced vegetables. It 130 Diseases of Greenhouse Crops is possible, however, to produce celery in the green- house which is of a quality far superior to that grown out of doors. The self-bleaching varieties such as the Kalamazoo seem to be well adapted for forcing. The White Plume seems to have a tendency to go to seed, and the Golden Self-blanching is subject to heart rot. Celery requires an abundance of mois- ture. A lack of it will cause such a setback to the plants that they may never recover. Too high or too low a temperature has the same detrimental effect. Diseases of the Celery Celery is subject to numerous diseases. Success with the crop demands great care in the production of healthy plants. Soft Rot, see Cauliflower, p. 126. Late Blight Caused by Septoria petroselini Desm. var. apii Br. and Cav. Symptoms. The disease first attacks the lower leaves of the stalk, producing irregular spots with- out a definite boundary line. When the spots be- come numerous the foliage withers and dries up (fig. 18, a.). The disease attacks the leaves as well as the stalks, rendering the affected plants useless for the market. In storage, plants affected with late blight will keep very poorly or rot altogether. The Organism. The fungus mycelium is hyaline, Fig. i8. Celery Disease. a. Septoria leaf spot, b. cross section through leaf to show relationship of fungus to its host, c. spores of Septoria petroselini {a-c after Coons), Celery Diseases 131 septate. The pycnidia (fig. 18, b.) are olivaceous, prraninent, and abundant in the spots. The pycnio- spores are filiform, straight or curved, hyaline and many are septate (fig. 18, c). Control. According to Rogers,* late blight may be controlled by spraying with 5-6-50 Bordeaux. The first two applications should be given to the seedlings in the seed bed. In the house the first spraying should be administered about six weeks after transplanting. Besides spraying, shad- ing also seems to keep the disease in check. In spraying celery, great care should be exercised to ap- ply a fine mist. Where this is overlooked, large drops of the Bordeaux mixture may be deposited on the leaves and stalks, which upon drying may deposit copper salt in sufficient quantity to injure the consumer. Sprayed celery should be carefully washed and dried before shipping. Early Blight Caused by Cercospora apii Fr. Symptoms. The trouble first appears on the outer leaves as pale blotches visible on both sides of the affected parts. The spots are irregular, an- gular in outline, limited apparently by the leaf veins, with slightly raised borders (fig. 19, a.). The spots later turn brown to ashy white. The Organism. The conidiophores are usually •Rogers, S. S, California Agr. Eipt Sta. Bui. 208: 83-115, 1911. 132 Diseases of Greenhouse Crops borne on the under side of the leaf, light brown, and in clusters. The conidia are hyaline, 3 to lo septate, cylindric (fig. 19, b.). Control. Early blight as well as late blight may be controlled by spraying with Bordeaux mixture. The Boston Market and Golden Heart varieties should be avoided because of their susceptibility to the disease. The White Plume seems to be resist- ant. CHAPTER n CUCUMBER {Cucumis sativus)' Cultural Considerations. Cucumbers are exten- sively forced for the winter or early spring markets, (fig. 20.) The houses generally used are either two-thirds or even-span and are provided with ground beds instead of benches. Unlike lettuce, cucumbers are not so sensitive to variations in soil texture. A great variety of soils may be used if, however, they are well provided with organic matter. Cucumbers require a night tempera- ture of about 65 degrees F. and about 85 degrees during bright weather. In cloudy weather, how- ever, the day temperature should be about lo to 15 degrees lower, otherwise the plants will become weak, spindly and susceptible to disease. Extreme care is required in watering the plants. Overwater- ing during cool, wet weather will greatly injure them by encouraging numerous diseases. Of the varieties which lend themselves to forcing are the Telegraph (English), and all strains of Dark Spine and White Spine among the American varie- ties. Diseases of the Cucumber Cucumbers under glass are subject to a large num- ber of diseases. 133 134 Diseases of Greenhouse Crops Leaf Curl Cause, physiological. Symptoms. The trouble is often manifested as a wilting of the edges of the leaves which curl into a spherical fonn. The wilted area soon dies, thus preventing any further development of the affected leaf. As the inner part of the leaf continues to grow and as it is restricted by its outer dead area, it as- sumes a convex form and a contorted margin, so that it curls up and assumes the shape of a ball. In advanced cases the stems, too, curl. The disease was studied by Stone * who believes that the cause of the trouble is overmanuring. Abnormal modifi- cations in the light, soil texture, and moisture condi- tions may frequently induce the same trouble. To prevent this disease the use of excessive manures should be avoided. As far as possible, conditions which favor weak soft growth should be eliminated. Malnutrition of Cucumbers Cause, physiological. Malnutrition generally results fr{Mn an overfer- tilization of the soil. This trouble has been care- fully studied by Haskins t who found it very preva- lent on indoor cucumbers. * Stone, G. E., Mass. (Hatch) Agr. Expt Sta., Bui. 87: 3-43, 1903. t Haskins, H. D^ Mass. Agr. Expt. Sta. Twenty-fifth Ann. Rept.: 71-76, 1913. < •J P u O u o O >< K 1-1 la b Cucumber Diseases 135 Symptoms. At first, the plants have a vigorous appearance, but soon turn yellow and fail to form fruit. The leaves of affected plants become spotted^ resembling somewhat mosaic. Cucumbers are often grown in the same beds for a number of years. Each year as new manure and fertilizers are added, the salt content of the soil becomes higher and more concentrated. Although there is an abundance of available food in the soil, the cucumber suffers because it is unable to stand a concentrated form of food. Chemical analysis of a normal and an overfed soil throws much light on this important subject. These analyses are given in the accompanying Table 17. Table 17 Average Composition of an Overfed Soil Com- pared with Normal Soil Total water soluble salts. Soluble nitrogen Soluble pota^ Soluble phosphoric add. . Soluble calduin oxide. . . . Soluble sodium oxide . Soluble magnesiuin oxide S(duble sulphates From Table 17 it is seen that an overfed soil has a marked increase of soluble plant food. If we should express this in terms of fertilizers it would make 3^ 136 Diseases of Greenhouse Crops tons of nitrate of soda, 6^ tons of high grade sul- phate of potash, 2 tons of 16 per cent, phosphate, and 1 ton of hydrated lime. To express it in terms of a mixed fertilizer it would amount to 14^^ tons of a formula testing 4 per cent, nitrogen, 23 per cent, actual potash and 2.25 per cent, available phosphoric acid. The injurious effect on cucumbers is not due to the excess of any one element but rather to the toxi- city of the combined excess of soluble salts. Physiological Wilt Symptoms. Cucumber growers often find that their plants wilt badly when subjected to the in- tense rays of the sunlight. This is especially true when bright weather follows a continued cloudy spell. This trouble is common in houses which are poorly ventilated, and where the plants are weak. Too high a temperature and poor lighting will great- ly favor wilting. The removal of these causes will effect a cure. Lack of Color in Fruit Cucumber fruit, especially of the White Spine va- riety, often becomes very white, thus commanding a lower market price. This discoloration is probably due to a lack of available nitrogen in the soil. It may be remedied by the application of one part liquid nitrate of soda to one thousand parts of water. Fig. 21. Cucumber Diseases. a. Mosaic, b. anthracnose. Cucumber Diseases 137 Mosaic or "White" or "Little Pickle" Cause unknown. Symptoms. The first sign appears as a yellow mottling near the stem end of the fruit. Later the light areas are found all over the cucumber, and the darker portions frequently form protuberances. Some fruits retain their green color and show the disease only by being distorted. The leaves become mottled light to dark green (fig. 21, a), and some- times wrinkled, while the stems and petioles are dwarfed and distorted. Affected leaves die prema- turely and are replaced by others, which in turn con- tract the disease. The trouble is spread principally by the melon louse. Aphis gossypii Glov., and to a lesser degree by striped cucumber beetle, Diabrotica vittata Fabr. Satisfactory methods of control are still wanting. Affected plants should be destroyed to prevent further spread of the disease. Bacterial Wilt Caused by Bacillus tracheiphillus Ew. Sm. The symptoms and the damage caused by this wilt will be found discussed under the muskmelon, p. 155. Recent investigations by Rand and En- lows * have shown that seeds from diseased plants fail to reproduce wilt. This is true not only for the cucumber, but also for all the other cucurbit •Rand, F. V., and Enlows, E. M. A., U. S. Dept. of Agr. Jour. Agr. Research, 6 : 417-434, 1916. 138 Diseases of Greenhouse Crops hosts which are subject to this trouble. Of the nu- merous varieties of cucumber, none shows promise of resistance to the disease. Angular Leaf Spot Caused by Pseudomonas lachrymans Sm. and Bry. Symptoms. The trouble is characterized by an- gular brown spots which tear or drop out when dry, giving a ragged appearance to the infected leaves. In the early stages of the disease a bacterial exudate collects in drops on the lower surface of the spots. This usually dries up and becomes whitish. It seems that angular leaf spots usually attack only the foli- age, rarely the fruit. The Organism. The parasite is a short rod with rounded ends, occurring singly or in pairs with a decided constriction, and occasionally in chains of twelve individuals or more. It is motile by means of polar flagella, produces capsules on agar and milk; no spores, and no gas is formed. The organism com- pletely liquefies gelatine in about three or four weeks. Little is known of methods of control. Damping Off, see Pythium, p. 28. Downy Mildew Caused by Fseudoperonospora cubensis (B. and C.) Rost. Symptoms. The disease appears on the leaves Cucumber Diseases 139 as yellowish spots, which have no definite outline. In a warm, moist atmosphere numerous spots coal- esce, and soon the affected leaves turn yellow and die. With cool temperatures, the spots seem to spread less rapidly. The disease appears to work on the older leaves, beginning on those at the center of the plant and working outwards. With infected plants the center of the hill is clearly marked by a cluster of yellow leaves. Diseased plants may flower profusely, but set no fruit. The few cucum- bers which are set are small, deformed, and unfit for the market. The Organism. The fungus derives its food from the host cells by means of suckers or haustoria. The mycelium is hyaline, non-septate; the conidiophores arise in small clusters through the leaf stomata and are branched and flexuous. The zoosporangia are hyaline but slightly violet, tinted in mass. Germina- tion of zoosporangia is by means of motile zoospores. The zoospores or sexual fruiting stage was first found on the host by Rostovtsev. Control. Downy mildew seems to be most prev- alent on greenhouse cucumbers planted in August. Those set in October seem to be free from it. Where the disease makes its appearance, it is advisable not to syringe the plants, but on the other hand to keep the foliage dry. Diseased plants or parts of plants should be destroyed by fire. Late planting in Sep- tember or October wherever practicable is also ad- vised. 140 Diseases of Greenhouse Crops Timber Rot Caused by Sclerotinia Ubertiana Fckl. Symptoms. The disease seems to attack the stem end of the plant nearest to the ground line. Af- fected stems at first water-soaked, then become invaded with a cushion of white mycelial growth. Rapid wilting, with no recovery, immediately fol- lows. As the affected plant dies, the shriveled stem becomes covered with black masses of fungous bodies, sclerotia. The same fungus also causes lettuce drop. For a description of the causal or- ganism and methods of control, see p. 151. Powdery Mildew Caused by Erysiphe dchoracearum D. C. Powdery mildew of cucumbers is not a serious greenhouse trouble. Like all powdery mildews, the causative fungus grows on the surface of the leaf, giving it a white mealy appearance. From the mycelium are produced erect threads which bear the summer spores of the fungus. The ascus or winter stage appears as minute dark-brown, rounded cap- sules enclosing a group of spore sacs within which are formed the ascospores. Control. The conditions which favor mildew are overwatering, lack of ventilation, lack of light, and too high a temperature. Proper attention to these factors will help to remove the cause and to effect a cure. Fig. 22. Cucumber Root Knot. Cucumber Diseases 141 Anthracnose Csaisedhy Colletoirichum lagenan'um (Pass.) Ell. and Hals. Symptoms. This disease is often serious on green- house cucumbers and muskmelons. It is seldom so in the fall and winter, but is most frequently met with in the spring of the year. Affected plants dry up and present a parched appearance. The dis- ease also attacks the cucumber leaves, forming round spots (fig. 21, b.), and on the fruit, deep cank- ers, thus ruining its market value. It is claimed by practical greenhouse men that the great difference in temperature between day and night, which is un- avoidable in the spring when the fires have gone out, favors infection. The Organism. In structure, Colletotrichum la- genarium resembles the organism of bean anthrac- nose. The cucumber fungus has a peculiar ability to remain dormant during the dry weather; but it is easily revived by moisture. The fruits of the fun- gus are borne in masses on the pustules which take on a salmon color. The spores are typical of all CoUetotrichums — that is, oval, one-celled, and hya- line. The setae in C lagenarium are not very plenti- ful. In pure culture it resembles C. lindemuthia' num; however, pathologically it is distinct from the latter, since numerous attempts by the writer and by others have failed to infect growing bean plants with the watermelon anthracnose or the watermelon with that of the bean. 142 Diseases of Greenhouse Crops Control. As soon as the disease makes its appear- ance the foliage should not be syringed, but kept dry. Spraying with 3-5-50 Bordeaux is recom- mended. Root Knot, see Nematode, p. 28 (fig. 22). Eggplant (^Solanum melongena) Cultural Considerations. Eggplants require as much heat as cucumbers. The night temperature should never run down below 60 degrees F. The day temperature may safely be maintained at 80 degrees or more, provided, however, sufficient ven- tilation is allowed. The best soil for greenhouse eggplants is a light sandy soil containing plenty of organic matter. Raised benches with bottom heat is preferred for winter forcing. The eggplant does not thrive under an excess of water. To obtain marketable fruit, the blossoms must be hand pol- linized to insure fertilization. Diseases of Eggplants Eggplants are subject to numerous diseases. Southern Wilt, see Tomato, p. 185. Damping Off, see Pythium, p. 17. Fruit Rot Caused by Phomosis vexans (Sacc. and Syd.). Symptoms. Fruit rot attacks all parts of the plant Fig. 23. Egg Plant Diseases. a. Phomosis spot on leaf, b. pycniospores, t. conidio- phores, d. stylospores (b-d after Barter, L. L.). Eggplant Diseases 143 except the roots. On the seedlings it causes a damp-, ing o£F. Young plants are attacked at the stem end OT an inch or two above the ground line as indicated by a constricted area at that place. On the leaves the trouble is manifested as large brown round spots which later become irregular and ragged (fig. 23, a.). The older spots are light purple in the center and are surrounded by a black margin. As they en- large the spots also invade the veins, midribs, and petioles, forming depressions. Diseased fruits are at first soft and mushy, but later become dry, shriv- eled, and mummified (fig. 24, a.). The Organism. Pycnidia are usually foimd on all parts of the attacked plant. Within the body of the pycnidia and intermixed with the conidio- phores (fig. 23, c.) and pycniospores (fig. 23, b.) are found filiform hooked-shaped bodies termed stylos spores (fig. 23, d.). Fhomosis vexans has been erro- neously referred to as Pkoma solani Hals; Pkoma vexans Sacc. and Syd., and Aschochyta hortorum Speg. Control. The seedlings in the seed bed should be sprayed with Bordeaux at least once before trans- planting. The plant in the house should be sprayed from four to eight times with either Bordeaux mix- ture or ammoniacal. copper carbonate. Anthracnose Caused by Gloesporium melengonea E. and H. Anthracnose on the e^plant attacks only the 144 Diseases of Greenhouse Crops fruit. The trouble is characterized by numerous deep pits which later become covered with salmon colored acervuli (fig. 24, b.). The latter are made up of myriads of spores of the fungus. Spraying for fruit rot will also help to control anthracnose. Root Knot, see Nematode, p. 28. Fig. 24. Egg Plant Diseases. u. Phomosis on fruit, &. anthracnose on fruit. CHAPTER 12 LETTUCE {Lactuca sativa) Cultural Considerations. Lettuce is extensively grown as a greenhouse crop (fig, 25). The best re- sults are obtained where the soil contains consider- able sand, especially where head lettuce is produced. This is also true for Coss lettuce. However, the Grand Rapids variety will thrive in any soil. Let- tuce is a heavy feeder, hence stable manure is often used exclusively. If the crop does not make rapid headway, nitrate of soda at the rate of one pound to 100 square feet of space may be applied. In using acid phosphate or potash only small quantities should be applied for fear of burning the plants. Lettuce requires an abundance of water and good drainage. High temperatures and humidity will produce weak, spindly plants. Careful ventilation may be the cause of preventing numerous diseases. In mild weather the ventilators may remain open even at night. This, however, should not be done during freezing weather. It is fortunate that lettuce seed retains its vital- ity for three or four years. This enables the grower to test out carefully the strains which he uses. 145 146 Diseases of Greenhouse Crops Diseases of Lettuce Top Burn Cause, physiological. Symptoms. In plants suffering from top bum a withering of the leaves is followed by the curling back of the tips and margins of the outer leaves, the affected areas becoming blackened to a distance of an inch or more from the margin. The condition great- ly disfigures the lettuce head and reduces its mar- ket value. Causes. The trouble may originate on a bright day following a cloudy spell. The greenhouse air is then saturated with moisture and consequently the lettuce leaves transpire very little. With the sudden appearance of strong sunlight, there is a rise in temperature, and a loss of moisture in the greenhouse air. Under these conditions, the foliage will transpire heavily. If the water given off by the leaves is greater than the roots are able to re- place, the leaves will wilt, and if this is continued for any length of time, the tissue along the leaf margin will wither and die. Control. A practical remedy for top bum is to saturate the greenhouse air with moisture on bright days which follow cloudy spells. This will prevent the undue transpiration of the leaves and its subse- quent bad effect. g s H Lettuce Diseases 147 Bacterial Blight Caused by Pseudomonas viridilividum Br. Symptoms. The disease seems to attack only the outer leaves of a head. The affected foliage is first covered with numerous watersoaked spots which en- large, fuse together, and involve the entire area of the affected leaves. The latter either soften or dry up, opening up the way for the entrance of other decay organisms, which may now attack the other- wise sound head. The Organism is rod-shaped, occurring singly, in pairs, or in chains, and it moves about by means of polar flagella. On agar, the young colonies are round with entire smooth margins; they are translucent, cream white in reflected light, but bluish in trans- mitted light. The older colonies are not always uni- form in color, but may take on yellowish bands or become mottled. The organism does not form gas and it liquefies gelatine slowly. It is not especially sensitive to sunlight. Control. Since the disease may be introduced with infected soil, soil sterilization is recommended. The SotTTH Carolina Disease Caused by Pseudomonas vitans Br. Symptoms. The disease may attack the stems or leaves. At first, diseased plants become pale and lose their normal green. Later the head wilts and rots (fig. 26, a.). The rot may be confined to the 148 Diseases of Greenhouse Crops outer leaves, or involve the whole head. Affected stems become brittle and may be readily broken. At first they are a blue green afterward becoming brown. The disease is met with in the field, but may also be introduced in the greenhouse. The Organism. Nellie Brown * has definitely proved that Pseudomonas vitans is the cause of the trouble which seems so prevalent in South Carolina. The causal organism is a short rod with rounded ends, motile by means of polar flagella (fig. 26, b.), one at each end; produces no spores, but capsules and pseudozoogloeae. It liquefies gelatin slowly and produces no gas. Control. The disease may be introduced with in- fected seedlings or soil. For the latter, soil steriliza- tion with steam or formaldehyde is recommended. Diseased seedlings should be discarded. The Kansas Disease Caused by Pseudomonas marginale Br. Symptoms. The disease seems to appear when the plants are half grown. At first the leaves wilt slightly in restricted areas at the margin. On the older leaves wilting starts at the tips. The affected areas fall over and gradually dry up. The vascular tissue then becomes affected and brown, then reddish, and finally black. The tissue of the dead parts on the leaves becomes dry and papery. •Brown, Nellie A., U. S. Dept of Agr., Jour. Agr. Research, ij: 367-388, X918. Fig. 26. Lettuce Diseases. a. Bacterial blight, b. Pseudomonas vitans, polar flagella stained with Casares-Gil's stain, c. gray mould rot; notice the numerous Botrytis fruiting heads on the wilted lettuce head. Lettuce Diseases 149 This disease does not cause a rot of the leaves. The trouble is confined mainly to the edges of the foliage, marring the appearance and the market value of the product. The varieties most afltected seem to be the Black-seeded Simpson, the Improved Hansen, and the Big Boston. Of the varieties less suscep- tible may be mentioned the Early Curled Simpson, and Vaughan's All Season. The variety Grand Rapids seems to be immune. The Organism. Pseudomonas marginale is a short rod, rounded at both ends and motile by means of polar fiagella. It forms capsules but no endo- spores, liquefies gelatin quickly and produces no gas. Control. Infected material should be destroyed* by fire. In watering, splashing should be avoided. Soil sterilization with steam or formaldehyde (see pp. 32-43) is recommended. Downy Mildew Caused by Bremia lactuce Reg. Symptoms. Affected leaves lose their natural green color and turn yellow. A careful examination will disclose a delicate downy web on the under side of the foliage which will have a wilted appearance. The downy web consists of the conidiophores of the fungus. These appear singly and are much branched. The conidia germinate by means of a germ tube. Downy mildew is a disease which is more troublesome in Europe than in the United States, and it is more serious on greenhouse lettuce 150 Diseases of Greenhouse Crops than on that grown in the open. In the field it usu- ally attacks fall lettuce. Downy mildew attacks not only lettuce, but also chicory and numerous other Compositae. Control. This disease is controlled in the same way as lettuce drop (see p. 151). Gray Mold Caused by Sderotinia fuckeliana De Bary. Symptoms. Gray mold attacks grapes in Europe but in the United States it is commonly met with on lettuce plants which are fully developed and somewhat overgrown. The disease is manifested by soft, watersoaked spots on the foliage, causing a wilting. The spots soon become coated with the fruit of a gray mold. The fungus has two stages, the Botrytis cinera Pers. stage, which is commonly found as a gray mold on wilted lettuce leaves (fig. 26, c.) ; the other is the winter or apothecial stage, known as Sderotinia fuckeliana. American botanists have not as yet been able to cormect these two forms. It seems, however, that IstvanfR * was able to con- firm the work of De Bary, who first indicated the re- lationship of Botrytis cinerea with Sderotinia fuckeliana. Control, see Lettuce Drop, p. 151. Lettuce Drop Caused by Sderotinia lihertiana Fckl. Symptoms. The term drop best describes the 'IstvanflS, G. De, Ann. de I'institut central amp£l. roy. Hon- grois: 183-360, 1915. Fig. 27. Lettuce Diseases. o. Drop (after Humphrey), b. Septoria leaf spot, c, same as &. but older spots, d. pycnida, e. pycniospores (af- ter Selby). Lettuce Diseases 151 symptoms of the disease. The first sign is a wilting of the lower leaves, which is immediately followed by a drooping of upper ones until the entire plant is involved. The affected plant has a sunken ap- pearance as if scalded with boiling water (fig. 27, a.). In examining a dead plant, a white cottony fungus growth is foimd on the under side of the lower leaves, and near the moist regions at the stem end. When the plants are fairly rotted, there appear on the cottony mycelial growth mentioned above, black bodies, or sclerotia, which vary in size from a pinhead to a grain of com. The three definite sjonptoms of the disease may be summarized: (1) drooping, (2) cottony-like mycelial growth on the under surface of the affected leaves, (3) the appear- ance of sclerotia. The latter help to carry over the fungus during the winter. After the sclerotia have been in the soil over winter, they germinate in the following spring by sending out small mushroom-like fruiting bodies known as apothecia. The latter con- tain small sacs or asci which bear the spores. Control. Lettuce drop is favored by high tem- perature, overwatering, and poorly drained beds, leaky roofs, and insufficient ventilation. To check the disease a low night temperature of 50 degrees F. should be maintained. The water should also be withheld and an abundance of ventilation given es- pecially during cloudy weather. Soil sterilization with steam or formaldehyde is also recommended. 152 Diseases of Greenhouse Crops Leaf Spot Caused by Septoria lactuce Pass, and Septoria consimilis E. and M. This disease is induced by two species of Septoria fungi. The symptoms produced by both are so near- ly alike that it is difBcult to distinguish one iroca. the other, except by microscopic examination. Pale brown discolored spots appear on the older leaves with numerous black pycnidia in the center (fig. 27, b-e.). The disease is of little economic importance, as it usually occurs late in the season, on plants which have nearly passed their usefulness. The Boston variety is considered resistant, while the Salamander and the Wonderful are more susceptible to leaf spot. Shot Hole Caused by Marsonia perforans E. and E. The disease is of little economic importance. Af- fected leaves are covered with dry spots which drop out, leaving irregular perforations. Along the bor- der of these holes, the causative fungus may be found abundantly fruiting. The disease attacks the mid- ribs of the leaves as well as the stem of the plants. It seems to be more prevalent under conditions of surface irrigation. With sub-irrigation, on the other hand, it is not found to cause any damage. Fig. 28. Lettuce Diseases. a. Lettuce rosette (to right diseased, and to the left healthy plant), b. Rhizoctonia eSEect on roots; to right healthy roots, to left two diseased ones. Lettuce Diseases 153 Cercospora Leaf Spot Caused by Cercospora lactuca Stev. This disease is as yet of no importance in the United States. The causal fungus attacks the older and lower leaves forming numerous irregular spots. Rosette Caused by Rhizoctonia solani Kuhn. Symptoms. The disease attacks young seedlings by causing a damping off. Transplanted seedlings show infection at an early stage. Unlike healthy plants, they fail to send out new leaflets. The gen- eral growth takes the form of a rosette. The axis bearing leaf remains stunted. The roots show nu- merous deep lesions, and in an advanced stage are considerably rotted (fig. 28, b.). For a description of the causal organism, see p. 20, and for meth- ods of control see Lettuce Drop, p. 151. Root Knot, see Nematode, p. 28. Mint {Mentha sp.) Cultural Considerations. Mint is often forced on a small scale. The plants are easily grown, and re- quire about the same indoor conditions as the let- tuce. Diseases of the Mint Indoor mint may be subject to but one disease of importance. 154 Diseases of Greenhouse Crops Rust Caused by Puccinia tnentha Pers. This disease attacks about thirty-five members of the mint family. All the three stages of the fungus, i.e., secidiospores, uredospores, and teleutospores, oc- cur on the same host. The disease is characterized by brown sori which are at first cinnamon colored and later become chestnut brown. Diseased leaves curl and dry up. The infected parts of plants should be destroyed by fire. MusKMELON {Cucumis meld) Cultural Considerations. Muskmelon culture is little different from that of the cucumber (fig. 29.). However, the former is very sensitive to cold drafts and sudden changes in temperatures. For forcing, the heavier types of soil seem to be more desirable than the lighter ones. The fertilizer requirements for muskmelons are practically the same as those for cucumbers. Muskmelons require an abundance of soil moisture, but are sensitive to overwatering. It is also essential to maintain a high hiimidity in the house during the period of active growth. Dur- ing pollination and the ripening of the fruit the above condition is unnecessary. The temperature should be about 70 to 75 degrees F. at night and from 80 to 85 degrees Fahrenheit during the day. Muskmelons, like cucumber blossoms, must be pol- linated artificially, since both male and female flow- Fig. 29. Typical muskmelon house, showing method of trailing and supporting fruit. Muskmelon Diseases 155 crs are distinct. The pollination is done by means of a camel's-hair brush, where the pollen from the male blossoms is rubbed on the stigma of the female flowers. Diseases of the Muskmelon Like cucumbers, greenhouse muskmelons are sub- ject to numerous diseases. Bacterial Wilt Caused by Bacillus tracheiphillus Ew. Sm. Symptoms. The symptoms of bacterial wilt are very striking. At first a few leaves of the plant are wilted. Soon after, the entire plant wilts and dies. Upon cutting through an infected stem, one observes a whitish viscid exudate that oozes out from the vascular bundles of the cut surface. If one places his finger on the viscid substance and then gently removes it, the bacteria will be strung out into nu- merous delicate threads resembling cobwebs. The disease works quickly, and the change of leaf color from bright to dull green is also sudden. Musk- melons, imlike squash, show no tendency to recover temporarily from wilt. Bacterial wilt is spread about through the bites of leaf-eating beetles, such as striped cucumber beetle {Diabrotica vittatd). The Organism. B. tracheiphilus is a short straight rod with rounded ends. The organism oc- curs singly, in pairs, or rarely in chains of four; it is 156 Diseases of Greenhouse Crops motile by means of flagella. It grows slowly on gelatine which is not liquefied. On potato cylinders growth is vigorous, resulting in a gray-white film with no changes manifested in the substratum. There is no gas production and the organism is aerobic. Control. Infection begins at a place of injury that has been produced by the bite or puncture of insects. Hence, any attempt to control wilt should first aim to control insect pests (see pp. 381-410). Downy Mildew, see Cucumber, p. 138. Powdery Mildew Caused by Erysiphe polygoni D, C. This disease is the same as the mildew which at- tacks cuciraibers and numerous other hosts. Mildew is prevalent on greenhouse melons. It is character- ized by powdery white patches on the leaves. For control, see p. 323. Mycosph^rella Wilt Caused by Mycospherella citrullina (Sm.) Gr. Symptoms. This form of wilt is often a serious greenhouse trouble. Grossenbacher * found that in- fection is localized at the nodes and not at the inter- nodes. The injury from Red Spider or from other sucking insects is perhaps responsible for opening •Grossenbacher, J. G, New York (Geneva) Agr. Expt. Sta. Tech. Bui. 9: 197-229, 1909. Fig. 30. MusKMELON Diseases. a. Alternaria leaf spot, b. Alternaria spore (after Schwarze). Muskmelon Diseases 157 the way to this disease. A characteristic of the trouble is that the edges of the infected areas are covered with an oily, green to raisin-colored gum. The older parts of the spots are either dark and gummy or gray and dry, bearing numerous brown pycnidia. The Organism. The perithecia are roundish, rough, dark brown to black, and almost superficial on the surface of the spots. The necks of the peri- thecia are hairy, the ascospores are cylindrical, two- celled, hyaline, and slightly constricted at the center. Control. Spraying with Bordeaux mixtures when the plants are about half grown and before the dis- ease appears is recommended. Spraying should be continued so that the growing parts arc kept cov- ered with the fungicide. Anthracnose, see Cucumber, p. 141. Leaf Blight Caused by Alternaria brassica van mgrescens Pegl. Symptoms. The disease begins as small round spots which gradually enlarge. These spots are dry, brown in color and made up of concentric rings or zones (fig. 30, a and b.). Usually the spots are very numerous and their presence causes the leaves to curl and dry up prematurely, leaving bare vines and un- protected fruit. As a result, the melons ripen early and have an insipid taste, and are very poor shippers. Leaf blight is most serious under field conditions. 158 Diseases of Greenhouse Crops Control. The disease may be kept in check by spraying with a weak solution of Bordeaux mix- ture. Southern Blight Caused by Sclerotium rolfsii Sacc. Southern blight, a disease that attacks a large va- riety of hosts, is a serious melon disease in the South- em States. The injury in most cases is confined to the foot of the stem, the girdling and rotting of which finally causes the death of the affected plant. In the case of the cantaloupe, the fruit itself is at- tacked, infection usually taking place at a point where it touches the ground. The disease appears first as a slight soft spot which enlarges quickly, changing the entire mass of the fruit to a mushy pulp. The exterior of the affected melon is rapidly covered with a white cottony growth consisting of the mycelium of the fungus. Later there appear numerous whitish bodies known as sclerotia which turn yellowish and then brown. They help to carry the fungus over the winter. For methods of con- trol, see pp. 32-43. Root Knot, see Nematode, p. 28 (fig. 31). Fig. 31. Root Knot of Muskmelon. CHAPTER 13 THE MUSHROOM, Agoticus caitipestrts L. Cultural Considerations. As a rule florists are not as yet giving the mushroom the attention and con- sideration which it deserves. It is a crop which adapts itself particularly well to growth under benches, so that it utilizes all the extra greenhouse space (fig. 32, a and b.). Like all other remunera- tive crops, it requires skill to insure its permanent success. Temperature. Mushrooms may be grown in to- mato houses. In this case, the day temperature should run from 60° to 70° F. and the night tem- perature about 55° F. It should never be allowed to fall below 50 degrees. At less than 50° the crop does not thrive, although the spawn in the soil may endure freezing temperature without being killed. Preparation of Soil. In preparing .the soil, fresh horse manure is mixed with loam as follows: To three shovelfuls of manure add one of loam, piled alternately in thin layers. This is kept for three da3^, but mixed every day in order to prevent the rapid fermentation or heating. This mixing is con- tinued until all danger of spontaneous combustion 159 i6o Diseases of Greenhouse Crops is over. At this stage, the manure loses its rank odor and is ready to be put in the bed. Preparation of the Beds. The beds should be lo- cated preferably under the center benches, and in- closed in rough boards eight inches wide and one inch thick. The boards are set on edge and raised slightly above the floor so that with a bed ten inches thick the top of the bed would not extend much above the upper edge of the board. A layer of pre- pared manure is then spread evenly over the bot- tom of the bed, to the depth of three inches, and firmly pressed down by pounding with a brick. Two other layers of manure, each three inches thick and firmly pressed down are laid on the first, making the bottom about eight inches thick. A thermometer is placed in the manure and the temperature watched until it registers about 90 degrees F. Spawning the Bed. When the temperature of the manure in the bed ceases to rise above 90 degrees, it is ready to be planted with the spawn. The lat- ter is usually bought in bricks, sixteen of which make a bushel. Each brick is broken into twelve equal parts, which are inserted about an inch deep in the manure bed with intervals of nine inches. The manure is then packed firmly over the pieces, leav- ing the surface of the bed smooth again. Two weeks after planting the spawn, the beds are coated with two inches of the mellow loam prepared as stated above. The loam should be neither dry nor wet, but simply moist. It should not be applied until it is certain that the spawn has commenced Fig. 32. tt. Healthy mushroom bed, b. mushrooms grown under the benches in the greenhouse (after Beach and Paddock). Mushroom Diseases i6i growing. This becomes noticeable as a bluish-white, moldy growth. The loam beds should be covered with a three-inch layer of excelsior to keep them from drying. The mushroom beds should be pro- tected frtan the drippings of the overhead benches by a roof of heavy waterproof cover. Watering. Care should be taken never to over- water the beds. It is necessary to apply enough water to keep the surface of the bed moist, but not soaked. In watering the excelsior is often rolled back or else water may be applied on top of it. Beach* recommends as the beds begin to bear that they be watered twice a week with nitrate of soda dissolved at the rate of one ounce to each gallon of water. It is applied with a watering can in a quan- tity sufficient to moisten, but not to soak the beds. To promote good bearing and to prevent a rapid ex- haustion, the beds are often coated over again with a layer (me and a half inches thick of fine mellow loam. Diseases or the Mushroom Mushrooms are subject to few diseases. There are but two which need concern the greenhouse man. Bacterial Spot Caused by Pseudomonas fluorescens (Fl.) Mig. This disease, although serious, seems to be re- * Beach, S. A, New York (Geneva) Agr. Expt Sta. Fourteenth Ann. Kept.: 33i-S4i> 1^95* i62 Diseases of Greenhouse Crops stricted as yet to the mushroom caves in St. Paul, Minnesota. The trouble was first described by Tolaas.* Symptoms. It is characterized by an unsightly spotting of the caps, the severity of which differs in the cultivated varieties, especially the large white kinds. The spots, which do not extend deep into the flesh, appear while the mushroom is in the but- ton stage, or when the cap is fully expanded. The spots are at first pale yellow, but later become a chocolate brown. Though the disease does not seem to reduce the yield, the market value of the spotted mushrooms is considerably reduced. The Organism, Pseudomonas fluorescens is a small rod rounded at both ends and motile by means of polar flagella. It is a facultative anaerobe; pro- duces no endospores, no gas, but liquefies gelatine. On beef and potato agar, it produces a shiny gray- ish white growth accompanied by a greenish pigmen- tation, which diffuses in the substratum. Control. Spraying the mushroom caps with solu- tions of benetol, sodium carbonate, or copper sul- phate seems to have no beneficial effect. On the other hand, fumigating the beds with sulphur before planting the spawn insures the production later of a clean crop of mushrooms. The amount of sulphur to use is about one and a half pounds to each tiiou- sand cubic feet of house space. 'Tolaas, A. S., Pbytopath. 5: 51-53, 1915. Mushroom Diseases 163 The Mycogone Disease Caused by Mycogone pemiciosa Mag. The Mycogone is a very destructive mushroran disease. The exact amount of its distribution in the United States is as yet unknown. However, if once introduced in a house, it is likely to ruin the en- tire crop. Symptoms. The symptoms of the disease are often various. The presence of the malady may be indicated by small tubercules on the cap and by a form of fluflFy white growth on the gills, which in- terferes with their normal development. The result is distorted caps and stipes, and finally, a general darkening and decay of the tissue. In severe cases, monstrous soft masses with thick white fungus coat- ings are observed in houses in which the disease is very prevalent. In this case, the afltected plants have little resemblance to mushrooms. They decay rapidly, and emit a very disagreeable odor. The Organism. The spores of Mycogone pemi- ciosa are very characteristic. They consist of two cells, the upper spherical, rough, and covered with warts, the lower hyaline and smooth. Both cells possess thick walls. Control. According to Veihmeyer,* there are no evidences that tend to show that the Mycogone dis- ease is carried with the spawn manufactured by the "tissue culture" method. It is very probable, how- ever, that the disease was introduced into this coun- •Veihmeyer, F. J, U. S. Dept of Agr. Bui. 127: 1-24, 1914. 164 Diseases of Greenhouse Crops try from France with imported virgin spawn col- lected at random from fields. The disease may be introduced into a new place with the manure and then spread quickly in a number of ways. Immedi- ate precautionary measures are essential for the con- trol of this trouble. Diseased plants when first no- ticed should be pulled out and burnt. Allowing these infected plants to decay in the beds is a sure means of spreading the fungus broadcast. The gain from keeping the beds free from diseased specimens will more than compensate for the trouble. At the end of the season the soil in beds should be carried away to a distance where mushrooms will not be grown, al- though it may be used for garden purposes, since the Mycogone disease is known to attack only mush- rooms. After the house has been thoroughly cleaned out, it should be disinfected with the formaldehyde gas method. This is carried out as follows: For every thousand cubic feet of house space use three pints of formaldehyde and twenty-three ounces of potassium permanganate. The potassium perman- ganate is placed in two or three earthen or wooden vessels, each having a capacity of one quart to every ounce of permanganate. When ready for the opera- tion, the mushroom house is sprinkled with water, the potassium permanganate placed in the recepta- cles, the formaldehyde is poured evenly over the permanganate, and the greenhouse doors are closed at once. They are kept closed for twenty-four hours and then opened to allow the formaldehyde fumes to escape. All lights must be kept away from the house Mushroom Diseases 165 while they are being fumigated since formaldehyde gas explodes upon coming in contact with fire. Mush- room houses thus treated may be thoroughly rid of the Mycogone disease, but care must be taken to prevent reinfection. It is hardly necessary to add that all tools and wagons which were used in connection with the in- fected houses should be disinfected before being used again. All such tools and vehicles should be washed in a solution of one pint of formaldehyde in twenty gallons of water. Throughout the process the oper- ator must exercise extreme care not to inhale any of the poisonous formaldehyde fumes. CHAPTER 14 PARSLEY {Carum petroselinunij^ Cultural Considerations. Parsley is easily forced and requires no particular care. Any of the curly- leaved varieties lend themselves to forcing. Diseases of Parsley Under greenhouse conditions parsley is subject to but few diseases. Drop, see Lettuce, p. 150. Late Blight, see Celery, p. 130. Pea (Pisum sativum) Cultural Considerations. Peas are seldom forced, although they could be easily grown in the green- house. No attempt should be made to grow them after March. They require a night temperature of 40 to 50 degrees F. and a day temperature of about 60 degrees. They are readily injured by higher tem- peratures. They thrive best in solid beds and re- quire an abundance of water and good drainage. The early dwarf varieties lend themselves well to forcing. 166 Fig. 33. ScLEROTiNiA Rot on Pea Pods. Pea Diseases 167 Diseases of the Pea Indoor peas may become subject to several dis- eases. ScLEROTiNiA TOt (fig. 33), See Lettuce drop, p. 150. Thielavia Root Rot Caused by Thielavia hasicola Zopf. Symptoms. Plants severely infected with Thiela- via have practically no root system, for the latter is destroyed by the fimgus as rapidly as they are formed. All that is left is a charred, blackened stub. The diseased host constantly attempts to produce new roots above the injured part, but these in turn become infected. Such plants linger for a long time, but fail to set pods which are of any value. The Organism. The mycelium of Thielavia hasi- cola is hyaline, septate, and branched. The Myce- lium becomes somewhat gray with age. Three kinds of spore forms are produced — endospores, chlamy- dospores, and ascospores. The endospores are so called because they are formed inside a special thread of the mycelium. This is the spore form that com- monly occurs in pure cultures of artificial media and on the host. The endospore case is formed on terminal branches with a somewhat swollen base and a long tapering cell. The endospores are formed in the apex of this terminal cell and are pushed out of the ruptured end by the growth of the unfrag- l68 Diseases of Greenhouse Crops mented protoplasm of the base. They are hyaline, thin walled, and vary frcnn oblong to linear in shape. The chlamydospores are thick walled, dark brown bodies borne on the same mycelium as the endo- spores. This type of spore is formed in great abun- dance on the host and particularly within the af- fected tissue. The ascospores are lenticular in shape and are borne in asci or sacs within black perithecia. This stage, however, has not been found on the pea nor in pure culture. Control. Since the causal organism is introduced with infected manure or soil, sterilizing the beds with steam or formaldehyde (see pp. 32-43) is recommended. Powdery Mildew, see Bean, p. m. Pod Spot Caused by Spherella pinodes (Berk, and Bl.)] Niessl. Symptoms. On the stem the trouble appears as numerous elongated lesions. These spread to such an extent as actually to girdle the aflEected stem. On the leaves are formed oval spots, grayish in the cen- ter, and limited by a dark band. The pods, too, become badly attacked and the symptoms there re- semble those on the stems. The disease works its way from the pods to the seed within. The Organism. The causative fungus has two spore stages. The pycnidia bear the hyaline, two- celled spores, and are formed within the dead tissue Fig. 34. Pepper Diseases. 0. Antbracnose, b. ^art of ascervtilis, showing seteae. c. anthracnose spores of Colletotrichum nigrum ib-c after Schwarze), d. sunburn. Pepper Diseases 169 of the affected stems, leaves, or pods. The pycni- dial stage is known as Ascochyta pisi Lib. The win- ter or ascospore stage has only recently been discov-^ ered by Stone,* who found it on pods and stems previously aflFected, and on culture media. The fun- gus may be carried frwn year to year as dormant mycelium within the seed, or in the ascospore stage. Control. Seed treatment will not be of any value since the fungus is hidden within the seed. No out- side treatment is capable of reaching the parasite within. Seed should be secured from localities known to be free from the disease. Susceptible varieties, such as French Jime, Market Garden, American Wonder, should be discarded. The Alaska variety is said to be more resistant. Pepper (^Capsicum annum). Cultural Considerations. Peppers are not diffi- cult to force, although they are not extensively grown on a oxnmercial scale in the greenhouse. Peppers thrive best at a temperature slightly lower than that required by cucumbers (see p. 133). The Sweet Mountain variety seems to lend itself best to forcing. Diseases of the Pepper The pepper plant is considered comparatively hardy, and its few diseases usually become trouble- some only when the crop is neglected. Sun Burn (fig. ^ d), see p. 94. *Ston^ R. £., Annales MycoL, xo: 564-5931 1913. 170 Diseases of Greenhouse Crops Anthracnose Caused by Glomerella piperata (E. and E.) S. Anthracnose is a serioiis disease which is usually confined to the fruit. Its symptoms are character- ized by round, soft, sunken, pale spots (fig. 34, a). The summer or conidial stage is known as Gleosporium piperatum E. and E. and is found as salmon colored pustules abundantly scattered over the spots. The ascospore stage may develop in pure, cultures of the fungus. Black Anthracnose Caused by Colletotrichum nigrum E. and H. This form of anthracnose differs from the disease described above only in that the spots turn jet black. The trouble attacks the young as well as the mature fruit. The winter or ascospore stage of the causa- tive fungus has not as yet been found. It is very probable that the fimgus (fig. 34, b-c) is carried over as viable mycelium on the infected fruit left over in the field. Both forms of anthracnose may be controlled by spraying with Bordeaux mixture. Fruit Spot Caused by Macrosporium sp. This disease, which is as important as anthracnose, attacks the fruit at the blossom end. The peppers that are attacked are half rotted, black, and moldy'. Pepper Diseases 171 Little is known about the causative fungus. It is probable that the disease has the same origin as the blossom end rot of tomatoes, and that the Macro- sporium fungus is only secondary. Spraying with Bordeaux mixture is recommended. Leaf Spot Caused by Cercospora capsisi H. and W. This disease is characterized by roimdish raised spots on the upper surface, at first brown, later be^ c(M3iing gray brown. They are limited by a dark zone, beyond which the leaf tissue is pale and chlor- otic. Where the spots are abundant the leaves turn yellow, wilt, and fall off prematurely. The conidiophores of the fungus are formed in clusters on both surfaces of the spots. The conidia are dilutely brown, clavate, and several septate. As a control measure spraying with Bordeaux mixture is recoaimended. Southern Blight Caused by Sclerotium rolfsii Sacc. Symptoms. Affected plants show a drooping of the young leaves at the tips of the branches. At night the plant seems to recover and it appears nor- mal the next morning. This recovery, however, is only temporary. Wilting generally follows, and after three or four days the leaves become completely yellow, wilt, droop, and die. In another day, the 172 Diseases of Greenhouse Crops stem of the plant loses its green color, dries up, and dies. On pulling out a plant freshly wilted, we find a shrunken discolored area at the foot of the stem, slightly below ground level. In more ad- vanced stages, the shrunken area is covered by a delicate web of white mycelial threads, and after the death of the plant numerous brown mustardlike sclerotia are found on the surface of the affected tissue. Control. The causal fungus is introduced in the greenhouse with infected soil or manure. Soil ster- ilization with steam or formaldehyde (see pp. 32- 43) is recommended. CHAPTER 15 RADISH {Raphnus sativus) Cultural Considerations. There are few green- houses near a large city which do not force radishes. The radish more than any other plant thrives best in full light. Shade favors the development of foliage over root. The varieties best liked by the market are those of the Scarlet Rose type. A light sandy soil which contains sufficient humus is ideal for forced radishes. Radishes need plenty of water. However, overwatering may favor damping off. The most favorable temperatures are 43 to 45 degrees F. at night and about $$ to 62 degrees during the day. In warm days the ventilators should be fully open. On cold days they may be opened a little at a time. Radishes are often intercropped with let- tuce or cauliflower. Diseases of the Radish Radish is subject to many diseases in common with the cauliflower and numerous other crucifers. Club Root, see Cauliflower, p. 122. Black Rot Caused by Fseudomonas campestris (Pam.) Ew. Sm. 173 174 Diseases of Greenhouse Crops Symptoms. Black rot on radish is confined mostly to the tender white-rooted varieties, especially the Icicle. The black-rot germ penetrates the lateral feeding rootlets, from which it works its way into the main root. In cutting across a diseased radish, its interior iibrovascular bundles are found to be blackened. Such radishes are useless for the mar- ket. The disease seldom attacks the red or the black-skinned varieties. For further consideration see Black Rot, p. 124. Scab Caused by Actinomyces chromogenus Gasp. Scab is not a common field disease of radishes. It is, however, found to be troublesome on the crop grown in greenhouses. The French Breakfast va- riety is commonly susceptible to the disease. The trouble may be expected if the crop is planted in a soil which previously produced a potato crop that was badly scabbed or where infected manure was used, or too much lime applied. For methods of control, soil sterilization with steam or formalde- hyde is recommended (see pp. 32-43). Damping Off Caused by Kheo sporangium asphanidermatum Ed. Symptoms. The disease seldom attacks the leaves. The injury is confined to the roots only. Diseased plants are flabby, pale or yellowish, with a tendency to wilt. The roots when pulled out will show that Fig. 35. Rheosporangium Rot op Radish. Radish Diseases 175 the rootlets have been rotted off and that the main root, too, has rotted at various intervals* (fig. 35). Control. This disease may be controlled in the same way as damping off (see pp. 32-43). Downy Mildew, see Cauliflower, p. 127. Damping Off, see Rhizoctonia, p. 20. Root Knot, see Nematode, p. 28. Rhubarb Cultural Considerations. Rhubarb is a popular greenhouse crop, and is extensively forced for win- ter use. Greenhouse rhubarb is superior in quality and in texture to the out-of-doors variety. The plant may grow in total darkness, but a diffused dim light is advisable. The roots before being planted should be thoroughly frozen for a few days, then given a short rest. In the milder climates of the South, the roots should be dried before planting. Both of these treatments will accelerate growth. When well established the plants need not be watered more than twice a week. The temperature for rapid growth ranges from 50 to ^$ or 60 degrees F. Under lower temperatures, the plants will re- quire a longer time to mature. The varieties which lend themselves well to forcing are the Paragon, Mammoth, Linnseus, Strawberry, and Victoria. *A description of the causal organism is given in the author's previous volume, "Diseases of Truck Crops and their Control," p. 2IO, 1918. (E. P. Dutton & Co., Nevf York.) 176 Diseases of Greenhouse Crops Diseases of the Rhubarb The Rhubarb is considered a very hardy plant. It is subject to but few diseases. Powdery Mildew Caused by Feronospora jaapiana Mag. This disease is fairly prevalent in Europe. Its presence in the United States is not definitely known. At any rate it is of little economic importance. Rust Caused by Fucdnia phragmitis Schum. Rust is a disease of little consequence. The secium known as Mcidium rubellum occurs on the rhubarb. The uredinia and the telia are found on Phragmitis. By destroying the Phragmitis the rhu- barb rust will be prevented. Anthracnose Caused by Vermicularia polygoni-virginica Schw. This disease is frequently found on old leaves of rhubarb grown out of doors. It is of little eco- nomic importance. Leaf Spot Caused by Ascochyta rhei E. and E. Like anthracnose, this trouble is of little impor- Spinach Diseases 177 tance to greenhouse rhubarb. The causal fungus causes irregular spots, which fall out and give the affected foliage a ra^ed appearance. Spinach {Spinacia oleracea) Cultural Considerations. There has developed lately a tendency to grow indoor spinach on a large scale. Growers who have tried it out find that it is as profitable a crop as lettuce. The cultural re- quirements of spinach are the same as those of let- tuce, see p. 145. If the soil is deficient in nitrogen an application of nitrate of soda will be very beneficial. The aim should be to encourage rapid growth, which, moreover, insures high quality. Vigorous broad- leaved varieties such as Victoria, New Zealand, and others are recranmended. Diseases of the Spinach Indoor spinach is generally subject to less diseases than that grown out of doors. Malnutrition Cause : An excess of acidity or a lack of soil humus. Symptoms. Malnutrition may be met with where CMiunercial fertilizers are used to the exclusion of organic manures. The margins of the veins of the leaves become yellow while the central part takes on a mottled appearance. The outer leaves are usu- 178 Diseases of Greenhouse Crops ally the first to suffer; soon, however, the entire plant exhibits similar symptoms and ceases to grow. Control. Where this disease is prevalent, the soil should be changed, or sufficient organic matter in the form of well rotted manure incorporated in the beds. Malnutrition as a rule is not prevalent in the greenhouse, for it is rare that a greenhouse soil is lacking in humus. Downy Mildew Caused by Peronospora efusa Rabenh. Symptoms. The trouble is characterized by yel- low spots of conspicuous size on the upper part of the leaves. On the under side of the leaves, and corresponding to the spots above, is seen a mat com* posed of the dirty white or violet gray fruiting bodies of the fimgus. The disease is often prev- alent in the field. The Organism. Downy mildew is caused by the fungus Peronospora efusa. The spores of the para- site are borne on branches, which generally emerge through the breathing pores or stomata of the lower part of the leaf and germinate by sending out a slender germ tube. Infection takes place when the germ tube penetrates the upper side of the leaf, gen- erally through the stomata. The winter stage or oospores may be found in the affected leaves. Control. All infected material should be de- stroyed. Water should be withheld, and plenty spinach Diseases 179 of ventilation allowed whenever possible. The plants may be sprayed with a standard fungicide. Anthracnose Caused by Colletotrichum spinacitz Ell. and Hals. Symptoms. It appears as minute, round, water- soaked spots on the leaves. These quickly enlarge and become gray and dry. In the spots will be found evenly-scattered, minute, dark tufts; these are merely fruiting pustules which also contain mi- nute black bristles or setse. The disease is not limited to any particular part of the plant. Infection may take place anywhere on the foliage, stems, or peti- oles. The spore pustules may be formed on the upper as well as on the lower surface of the leaf. Under moist conditions, the pustules take on a sal- mon tinge, indicating that there is an abimdance of spores formed at that time. The spores may be carried frcMn leaf to leaf and from plant to plant by insects, wind, or rain water. In badly infected beds, picking should not be done when the leaves are wet. Infected material should be destroyed by fire. The fungi Entyloma ellissii Hals, Phyllosticta chenopodii Sacc, Cladosporium macrocarpum Preuss, and Heterosporium variabile Cke. do not seem to trouble indoor spinach but are rather serious out of doors. CHAPTER 16 TOMATO (JLycopersicum esculenium) Cultural Considerations. The tomato is one of the three most important greenhouse vegetables. It is perhaps more difficult to grow than either lettuce or cucumbers. Great skill is required in the heating, watering, ventilating, and pollinating. To overlook any of these factors may result in failure. Of the numerous varieties which lend themselves to forcing the following are the most preferred by the Ameri- can and English growers: American Varieties English Varieties Beauty Best of All Boimy Best Carter's Sunrise Earliana Comet Magnus Frogmare Stone Globe Lorillard Peerless Sterling Castle. The tomato thrives best in a medium heavy loam. The plants are heavy feeders. The fertilizer must be well balanced mixtures. The nitrogen, for in- stance, should not take the place of the potash or 180 Tomato Diseases i8i the phosphoric acid. Tomato plants require a lib- eral supply of water. However, overwatering will encourage numerous diseases. On bright, sunny days there is little danger of overwatering, but great care is required not to overwater during cloudy weather. The temperature for greenhouse tomatoes is very important. At night and on cloudy days it should be maintained at about 60 degrees F. During bright, suimy days higher temperatures will not be harmful. The house should be given all the ven- tilation possible. Even during cold days, the ven- tilators should be opened slightly at frequent in- tervals while a close watch should be kept on the indoor thermometer. Diseases of Tomatoes Greenhouse tomatoes are subject to a large num- ber of diseases. Many of these are of economic importance. Hollow Stem Cause, physiological. Symptoms. Hollow stem is a trouble manifested by seedlings in the bed, or after transplanting. The central portion of the head of the plant remains green while the lower leaves turn yellow. In se- vere cases, affected plants fall over as in damping off, with the absence, however, of signs of rotting. i82 Diseases of Greenhouse Crops Such plants when examined are found to have hol- low stems and seem too weak to stand up. Cause. There are several causes, any one or all of which may lead up to hollow stem. ( i ) A highly nitrogenous fertilizer applied to the seed bed to force the seedlings. (2) An abundance of water supply to make the fertilizer quickly available. (3) Sow- ing seeds of a rapid growing variety. (4) Trans- planting without hardening off. (5) Transplanting into a dry soil. Control. It is evident from what has been said that the fertilizer in the seed bed should be well balanced. Care should be taken to prevent the seed- lings from becoming leggy, and to see that they are properly hardened before transplanting. The Stone and its related varieties seem to be more resistant to hollow stem. On the other hand, the Dwarf Champion seems to be especially susceptible to hol- low stem. Winter Blight Cause, vmknown. Symptoms. This disease seems to be very preva- lent on forced tomatoes in the United States and Canada. Howitt and Stone,* who have recently studied this disease, describe it as follows: The leaves show distinct brown or blackened, angular, diamond-shaped spots scattered between the larger veins. When the spots are numerous and close to- gether they appear as a distinct pattern. In a more •Howitt, J. E., and Stone, R. E., Phytopath. 6: i(i-i66, 1916. Tomato Diseases 183 advanced stage, the primary and secondary veins also become browned. Afltected stems are peppered with minute brown lesions, irregularly scattered, and apparently superficially seated. In advanced stages, however, the lesions seem to work deeply into the vascular bimdles. On the fruit the disease appears as surface lesions which are variously shaped. The surface of the spot may be unbroken and smooth, or rough and scabby. In advanced stages, the super- ficial lesions work in deeply in the flesh of the fruit. Upon maturing, the affected areas fail to take on the normal color. Such fruit is spotted and scabby, and is worthless for market purposes. Up to the present, the exact cause of the disease and methods of control are unknown. It seems that the trouble is not caused by a pathogenic oi^anism, but rather by srane unknown chemical or physical derangement of the soil. Blossom End Rot Cause unknown. Blossom end rot, also known as point end rot, may be found wherever tomatoes are grown. It is a disease of the fruit only. In some seasons fifty per cent or more of the fruit crop is ruined by it. It seems to be serious in dry weather and on light soils. Symptoms. Infection is manifested as a water- soaked spot at the blossom end of the fruit (fig. 36, a.). The size of the spot may be that of a pin- head, or it may spread so rapidly as to involve half 184 Diseases of Greenhouse Crops of the tomato. A few days later, the water-soaked spot becomes black and leathery and ceases to make further progress. Complete rotting of the fruit may be brought about by secondary invasions. Plants subject to frequent slight wilting produce a greater number of defective fruits. There seems no doubt but that the water supply in the soil is an important factor in limiting or increasing blossom end rot. The factors of drainage and cultivation are, therefore, important considerations. Although dry soils and drought favor the increase oi the dis- ease, the state of health of the plant itself seems equally important. The use of fertilizers, too, seems to influence the trouble. Heavy applications of manure or of pot- ash seem to increase the rot, as do fertilizers in the form of ammonium compounds. This is especially true on sandy loams. On the other hand, nitrate of soda or lime acts as a check. In controlling blos- som end rot, the moisture of the air in the green- house seems also an important factor. On bright, simny days, it is not advisable to keep the air dry. However, care should be taken not to keep the air of the house dry during the night, as this encourages numerous fungous diseases. Sunburn Tomatoes are often burned while they are on the vines by strong sunlight beating on the exposed fruit. This results in a scalding of certain parts, loss of Tomato Diseases 185 color, and a local drying which produces white spots with a dry, peppery appearance. Such fruit is unfit for the market. Control. In houses where sunburn is prevalent it is advisable to have the house shaded and to plant varieties that have a dense foliage. Mosaic Cause unknown. A lengthy discussion on mosaic has already been given on p. io2. Mosaic on tomato is a common field and greenhouse trouble, conspicuous on stalks, fruit, and leaves. On the leaves it is manifested as a mottling of yellow areas on the tissue that causes the leaves to warp and grow unevenly. In severe cases the normal leaflets are replaced by a filiform or fem-like structure, with a striking dissected form. The blossom of the diseased plant usually drops off, and the few fruits that are set are small and de- formed. Southern Wilt Caused by Pseudomonas solanacearutn Ew. Sm. Symptoms. Infected plants usually wilt rapidly without losing their green color. In large leaves, the main axis is bent downward in a drooping way. With the young plants the stems and foliage also droop and shrivel. The vascular system of such plants is browned, indicating the presence of the causative organism within. Upon cutting across a freshly wilted stem, one observes that a dirty white i86 Diseases of Greenhouse Crops to brownish white slime that is not sticky oozes out. In soft and rapidly growing plants, the whole pith is often converted into a watery slime. In toma- toes and eggplants the disease seldom attacks the fruit but is confined to the vegetative parts. Southern wilt attacks not only the tomato and eggplant, but it also causes a serious disease on po- tato, tobacco, peanut, nasturtium, ragweed, impa- tience, and verbena, in the open. The Organism. Pseudomonas solanacearum is a medium-sized rod, with rounded ends and motile by means of polar flagella. Pseudo-zoogloeae are common in old cultures. No spores are formed; on agar-agar, colonies are white, then dirty white, after- wards becoming brown with age. The organism does not liquefy gelatine and produces no gas. Control. All diseased plants should be carefully pulled out and destroyed by fire. The house should be given all the ventilation p>ossible and water with- held for a while. Syringing of the plants should cease until the disease subsides. In watering care should be taken not to splash soil particles on the plant. All insect pests whether sucking or biting should be controlled, as these usually help to spread the disease. This trouble is likely to be prevalent in greenhouses in the Southern states. Damping Off. See Pythium. Late Blight Caused by Phytophthora infestans (Mont.) DeBy. Tomato Diseases 187 Late blight is a disease of frequent occurrence on greenhouse tomatoes. Symptoms. Affected plants appear as though killed by frost. The disease first shows itself as small blackened areas on the leaves, stems, and fruits. These rapidly increase in size and cause the premature death of the affected host. Fruits which may not show signs of disease will develop the trouble in transit if coming from infected houses. The Organism. The mycelium of the fungus is hyaline, non-septate. As shown by Melhus* and others, the mycelium may be carried from year to year within the infected tubers. In fact this is but one way by which late blight is distributed. Through the stomata of the infected leaf emerge the slender conidiophores bearing the ovoid conidia. According to Melhus the conidia of Phytophthora infestans may germinate either directly by a germ tube or by the production of zoospores as in Pythium. The best germination occurs at the optimum tem- perature, which lies between lo and 13 degrees C. (50-57 degrees F.). The conidia may be killed by exposure for six to twenty-four hours to dry atmos- pheric conditions such as exist in an ordinary room. Frost which kills the top of the plants will also kill the conidia of Phytophthora. Light does not hinder germination and therefore has no inhibiting effect on infection. Investigation fails to show that PAy- tophthora infestans produces sexual spores or 00- * Melhus, I. E., U. S. Dept of Agr. Jour. Agr. Research, $ ■ S9-fi5i 191J. l88 Diseases of Greenhouse Crops spores within the affected tissue of the leaf or tuber. However, Clinton succeeded in developing what ap- peared to be oospores of the fungus in pure culture on oat agar. The oogonia appear as swollen terminal heads, cut off from the main thread by a cross wall. The antheridium resembles that of P. phaseoU. Ma- ture oospores have a medium thick, smooth, hyaline wall. How the oospores germinate is unknown. Control. Late blight of tomatoes may be con- trolled by spraying. The best results are obtained by using 5-5-50 Bordeaux. Buckeye Rot Caused by Phytophthora terrestria Sherb. Buckeye rot is a disease which attacks the fruit. The trouble seems to be new and has been recently described by Sherbakoff.* So far as is known, the disease has appeared only in Florida. Symptoms. The disease, as the name indicates, appears as pale to dark greenish-brown zonate spots on the fruit. The rot is hard and somewhat dry when the fruit is green, but becomes softer as the tomato ripens. It usually begins at a point where the fruit touches the ground, which is most com- monly at the blossom end, and might be mistaken for blossom end rot were it not for the characteristic zonations. The Organism. The mycelium is at first continu- ous, then septate. Conidia germinate by means of * Shetbakoff, C. D., Fhytopath, 7:119-129, 1917. Tomato Diseases 189 swarm spores. Chlamydospores are common, oospores frequent on cornmeal agar. Besides tomato fruit, P. terrestria causes a foot rot of citrus trees and a stem rot of lupines. Control. Fruit destined for distant markets should not be packed as soon as it is brought in from the house. If possible it should be kept a few days to allow for possible rot to develop so that the af- fected ones may be culled out and destroyed. Spray- ing with Bordeaux mixture is also recommended. Leaf Spot Caused by As cocky ta lycopersici Brun. This disease is of common occurrence but of lit- tle economic importance. It produces brown circu- lar spots which enlarge and change to grayish brown in color. Fruit Rot Caused by Phoma destructiva Plowr. Symptoms. On the fruit the disease is character- ized by conspicuous dark spots on the side and at the stem end of both green and mature fruit. On the surface of the largest spots, numerous dark pycnidia may be seen. Besides attacking the fruit, the disease may also infect the foliage, causing dark spots which resemble those on the fruit. Affected leaves shrivel, droop, and sometimes drop off. The disease seems to be unable to attack potatoes or peppers. 190 Diseases of Greenhouse Crops The Organism. The mycelium forms a dense net- work of fungal threads within the host tissue. The pycnidia are subglobose, carbonaceous, smooth, slightly papillate, and with a distinct central pore. The pycnidia are scattered and few. Leaf Spot Caused by Septoria lycopersici Speg. Symptoms. The first indications of the disease are minute water-soaked spots on the underside of the leaves. With time, these increase in size and become circular in outline with a definite margin. The spots become hard, dry, dark, and shrunken, and when numerous they coalesce into large blotches, involving the entire leaflets and leaves; the latter soon droop, dry, and cling to the stalk, until broken oif by the wind or by any other jar. Within the spots are formed minute black, glistening pycnidia while the spores exude yellowish mucilaginous drops. On the stems, the spots are similar to those on the leaves, although they are not so clearly defined, nor do they work in deep enough to form cankers. Spots may also occur on the calyx and on the fruit. The disease, however, is usually a foliage trouble. Of the more resistant varieties may be mentioned Mikado, King Humbert, Wonder of the Market, and Up to Date. Of the medium resistant varieties may be mentioned Alice Roosevelt, President Gar- field, Prelude, Ponderosa, and Magnum Bonum. Tomato Diseases. 191 The Trophy and Ficarazzi are very susceptible varieties. The Organism. The mycelium of Septoria lyco- persici is hyaline and septate. The pycnidia are globose ; the pycnospores are hyaline, needle-shaped, many-septate, and lose their vitality when exposed to ordinary room temperature for about four days. Control. The disease often starts on the seedlings in the seed bed. It is important, therefore, to start with a clean seed bed soil. Seedlings should be sprayed with 4-4-50 Bordeaux before being trans- planted. In the house, the plants should not be worked when wet. Spraying with 4-4-50 Bordeaux IS recommended. Anthracnose Caused by Colletotrichum phomoides (Sacc.) Chester. Anthracnose is a disease to which ripe tomatoes are especially subject. The losses are often con- siderable both in the house and in transit. Symptoms. The spots are at first small, but they soon enlarge. They are discolored, sunken, wrinkled, with distinct central zones, closely resembling the anthracnose of apple. In moist weather, the spots become coated with a salmon-colored layer which consists of the spores of the fungus. The Organism. In structure, C phomoides is lit- tle different from other Colletotrichums. The setse of the fungus aire very numerous, thus giving the 192 Diseases of Greenhouse Crops acervuli a black appearance. The conidiophores are short, and the conidia, oblong, hyaline and one- celled. Control. Anthracnose depends upon a moist at- mosphere for its activity. Spraying with Bordeaux is recommended. Leaf Mold Caused by Cladosporium fulvum Cke, Leaf mold is very troublesome in the greenhouse. In some of the Southern States, however, it is found on field tomatoes also. The disease is favored by a damp, moist atmosphere. Symptoms. The mold appears as rusty ciimamon, colored irregular, feltlike spots on the underside of the leaf (fig. 36, b), the upper part of which turns brown, then black. The affected foliage finally curls and dies. The Organism. The conidiophores of the fimgus break through the cuticle of the epidermis in a dense crowded mass. The conidia are few and are borne on the tip ends of the condiophores, which are spar- ingly branched and knotty. The conidia are elliptic or oblong (fig. 36, c), 1 septate. Control. The effects of the disease are seldom disastrous if infection starts when the fruit has set and is well developed. An early infection when the plants are still young may result in the failure of the crop. Careful and thorough spraying with Bordeaux 4-4-50 before the disease appears is rec- ommended. Spraying should be done once every Fig 36. Tomato Diseases. a. Various stages of blossom end rot, b. Cladosporium leaf mold, c. fruiting stalks and spores of Cladosporium ftilvum ic. after G. Massee). Tomato Diseases 193 two weeks and should cease about five days before the fruit is picked. If the disease becomes well es- tablished in a house, spraying will prove of little benefit. In that case, the house should be emptied of all vegetation, the soil sterilized with steam or formaldehyde (see pp. 32-43), and wherever possi- ble the house, too, should be fumigated with formal- dehyde and potassium permanganate (see p. 164). Black Rot Caused by Macrosporium solani E. and M. Symptoms. Black rot is a fruit, stem, and foliage trouble. The spots are black, dry, slightly wrinkled, and extend deep into the interior tissue (fig. 37, a and b.). The Organism. The mycelium of the fungus at first varies in hue from hyaline to brown, then turns black. The conidiophores and conidia are dark, with three to six transverse and one to two longi- tudinal septse (fig. 37, c). Spraying with Bordeaux mixture is recommended. Sleeping Sickness Caused by Fusarium lycopersici Sacc. Sleeping sickness is a tomato trouble. It is usu- ally brought in with diseased seedlings. Symptoms. Infected plants become pale, the leaves wilt and droop and never recover (fig. 38, a.). The droopiness of a diseased plant gives it a 194 Diseases of Greenhouse Crops sleepy appearance, hence the name of the disease. On splitting open a diseased root or stem, one finds that the interior vascular bundles are brown, due to the presence of the parasite (fig. 38, b.). The Organism. F. lycopersici is a soil fungus which may be introduced with infected manure or seedlings. The fungus greatly resembles F. oxy- sporum. The conidia are hyaline to yellowish, fal- cate, acute (fig. 38, c and d.). Control. Spraying will not control this malady since the parasite lives internally and cannot be reached by external applications. The selection of resistant varieties may offer a means of conquering this trouble. Soil sterilization with steam or for- maldehyde is essential. Black Mold Caused by Fumago vagans Pers. Black mold usually follows the attacks of the white fly. The same fungus also attacks nastur- tiums grown indoors. The fungus appears as a con- spicuous olive-black growth on the upper part of the leaves. The fungus in this case is not parasitic, but usually grows on the honey dew secreted by the white fly. Although the fungus is not parasitic, its presence on the leaves is undesirable since it inter- feres with the absorption of light by the plant. In controlling white fly, the black mold fungus will also be checked. Fig. 37. Tomato Diseases. a. Cluster of tomatoes, affected with black rot, h. black rot on stems, c. germinated spore of Macrosporium solani (c. after Schwarze). Fig. 38. Tomato Diseases. o Sleeping sickness, 6. cross section of fibrovascular bundle of infected tomato stem showing mycelium, c. spores, d. chalmydospores (b-d after Schwarze). Tomato Diseases 195 Rhizoctonia Fruit Rot Caused by Corticium vagum B. and C. var. solani Burt. This form of rot makes its appearance at the place where the fruit touches the ground. The dis- eased area bec(Knes chocolate-colored, and the epi- dermis slightly wrinkled. The rot extends into die interior pulp, turning it brown and dry. For a further description of the causative fungus, see p. 20. Root Knot, see Nematode, p. 28. Broom Rape Caused by Orobanche ramosa L. The parasite fastens itself to the tomato roots whence it derives its food. The parasite produces a base of considerable size below ground from which a cluster of branching stems and bluish-yellow flow- ers appear above ground. The same parasite also attacks the hemp and tobacco out of doors. Fumigation Against White Fly The tomato is a favorite host for the white fly. The different conflicting results obtained by grow- ers in the fumigation treatment may be attributed to the use of widely different varieties of plants. The variations may also be partly due to tightness or looseness in construction of the greenhouse. Inves- 196 Diseases of Greenhouse Crops ligations by Warren and Voorhees* have shown that tomato varieties such as Lester Prolific, Elongated Sparks, Earliana and Station Yellow recover from the first fumigation with almost no injury. Under the same treatment, Eclipse and Fragmore's Selected suffer lightly, while Stone, Lorillard, Beauty, Per- fection, and Best of All become seriously injured. Tomato plants injured by night fumigation usually show no ill effect until about four o'clock the follow-" ing day, when they wilt. If lightly injured the tops usually die. Fumigation for fifteen minutes with potassium cyanide, one ounce to each 1,000 cubic feet of glass, during the dark is satisfactory for indoor tomatoes. The house at that time should be cool and dry (fig. 39, a-c). •Warren, G. F., and Voorhees, J. A., New Jersey Agr. Expt Sta. Twenty-seventh Ann. Rept.: 242-246, 1906. Fig. 39. Effect of Fumigation on Tomatoes. a. Fumigated 35 minutes in dark, c. fumigated 15 minutes in daylight, slight injury, 6. fumigated 30 minutes in daylight, severe injury (after G. F. Warren). PART IV DISEASES OF ORNAMENTALS CHAPTER 17 ALTERNANTHERA {AlterTicmtkera sp.) Cultural Considerations, see Coleus, p. 245. Diseases of the Alternanthera The Alternanthera is comparatively free from dis- ease and it is generally considered a hardy plant. Leaf Blight Caused by Phyllosticta sp. Symptoms. Alternanthera blight was first re- ported by Halsted* as being very serious in green- houses of the eastern states. It is especially severe in the "cutting" benches. The trouble is character- ized by a premature defoliation. The affected leaves coil up and drop off. In an early stage, the leaves become spotted merely, and it is only when the spots become numerous that the foliage drops off. The trouble is usually overlooked, because of the variegated foliage of the host. The cause of the blight is a Phyllosticta fungus, probably the same * Halsted, B. D., New Jersey Agr. Expt Sta., Thirteenth Ann. Kept.: 299, 1892. 199 200 Diseases of Greenhouse Crops as P. amaranthi, which attacks the pigweed, Amaran- thus retroflexus. Control. It is probable that spraying with a standard fungicide will control the trouble. Root Rot Caused by Rhizoctonia solani Kuhn. This form of injury is commonly met with in propagating benches of Altemanthera. The young cuttings often rot off before setting roots. On well established plants, the Rhizoctonia fungus is found as strands on the sides of the branches which touch the ground. In this case there is apparently no in- jury. It seems that the reddish varieties of Alter- nanthera is covered with more Rhizoctonia strands than are the green or the variegated varieties. For a description of the causal organism and methods of control, see p. 20. Antirrhinum {Antirrhinum Majus). Cultural Considerations. Antirrhinums have be- come important plants, forced primarily as cut flowers. The plants require a light sandy loam com- post. In filling the benches, we must avoid fresh and undecomposed manure. It is necessary also to avoid the excessive use of nitrogen. Where this is overlooked, the flowers will have a tendency to "sport" and possess too much yellow color, which is objectionable to the trade. Some growers prefer to Antirrhinum Diseases 201 add to the soil a liberal application of rock phosphate and finely ground limestone. Antirrhinums thrive very poorly in wet soils. The plants should not be syringed in winter and especial care should be taken in watering on cloudy days. The plants are not in- jured by a night temperature of 45 degrees F., al- though 48 to ^s degrees suits them' best. The day temperature should never run above 70 degrees F. Diseases of the Antirrhinum The antirrhinum, although considered a hardy plant, is subject to several diseases, most of which are of economic importance. Rust Caused by Puccinia antirrhini Diet, and Halw. Symptoms. The Uredo stage is the one most commonly found. It is manifested as small round- ish, reddish brown pustules, usually grouped circu- larly on the under side of the leaf or on the stem (fig. 40, a and b). The affected tissue becomes yel- low. The fungus was first described by Dietel* who foimd the Teleuto and the Uredo stage on specimens collected in California. The fungus is very com- monly foimd to attack snapdragons out of doors. It is also a serious trouble to growers of greenhouse plants. However, the Teleuto stage is not fre- •Hedwigia, 36:298, 1897. 202 Diseases of Greenhouse Crops quently met with. The exact life history of this fungus is as yet imperfectly known. Control. In the greenhouse, the disease is only prevalent on snapdragon propagated by cuttings taken from outdoor plants. In this case, the dis- ease is brought in directly with infected cuttings. The only remedy known is to use healthy cuttings. The safest is to use plants started from seeds sown indoors. Anthracnose Caused by Colletotrichum antirrhini Stew. Symptoms. Anthracnose is a common disease on greenhouse and garden snapdragons. In the green- house, it is more troublesome in the fall and spring. The disease attacks the stems (fig. 40, d) in all stages of development. It appears as a large spot on the stems or lateral shoots, resulting in their death (fig. 41, a and b). The spots are at first dirty white with a narrow border. Soon, however, the center turns black and under conditions of moisture, becomes covered with the acervuli of the causal or- ganism. On the leaves (fig. 40, d) the spots are circular, slightly sunken, at first yellowish green with indefinite outline, and later becoming dirty white or greenish, definitely outlined and limited by a narrow brown border. The spots, when nu- merous, spread and blend together. The affected foliage shrivels, clings to the stems and dies. Fig. 40. Antirrhinum Diseases. a. Rust on leaves, h. root knot, c. Uredo spores of Puccinta anttr- rhini (after Schwarze), d. anthracnose lesions on stems and leaves, e. sec* lion through an acervulus of Colletotrichum antirrhini f. spores of C. antirrhini, (d-f after Stewart, F. C). Antirrhinum Diseases 203 The Organism. The stroma is well developed; the conidia are straight to curved, with both ends rounded. The conidiophores are short, the setae abundant, dark brown, simple, and mostly straight (fig. 40, e and f). Control. The disease is often introduced in the greenhouse with infected cuttings. Cuttings should therefore be secured from healthy plants. This disease attacks only the snapdragon. It should therefore be an easy matter to prevent its introduc- tion indoors. If the disease makes its appearance, spraying with Bordeaux mixture should be resorted to. All diseased material should be destroyed by fire. Branch Blight Caused by Phoma poolensis Taub. Symptoms. The disease seems to be confined to the tender and growing shoots. It seldom affects the older and more woody stems. Affected parts wilt, and become discolored without showing any definite spotting. Later, however, numerous pycni- dia appear on the dead parts. The Organism. — Stewart* has proved by artificial inoculation that the causal organism is a parasite. The writer's investigation of this organism has con- firmed the work of Stewart. In 1916 and 1917, a careful study of this disease was made, as it occurred in several greenhouse establishments in San Antonio, •Stewart, F. C, New York (Geneva) Agr. Expt Sta. Bui. 179: 109-110, 1900. 204 Diseases of Greenhouse Crops Texas. It was proved definitely that the organism is parasitic and that it was also apparently an unde- scribed species to which the name Phoma poolensis Taubenhaus was given. The pycnidia are minute, numerous, black, with distinct mouths (ostioles). The spores ooze out in a colorless gelatinous rope- like mass. They are small, elliptical, hyaline, and one celled. Control. The methods of control for this disease should be the same as those used for anthracnose. Blight Caused by Septoria antirrhini Desm. This disease is greatly dreaded by English gar- deners. It was first described by Chittenden* who claims that it is very prevalent in Great Britain. Fortunately, it is not yet known to occur in the United States. The disease is characterized by a general blighting and dying of the leaves and branches. Wilt Caused by Verticillium sp. This disease, although new, is prevalent all over the United States. Little is known of the disease and of the causal organism. The Verticillium, how- ever, may be introduced with infected soil or ma- nure, or with diseased cuttings. To prevent the 'Chittenden, J. F., Jour. Roy. Hort Soc 35: 216-217, i909- Fig. 41. Antirrhinum Diseases. Healthy plant, b. plant killed by anthracnose (a and b after Stewart, F. C). Aspidistra Diseases 205 disease from getting a foothold in the greenhouse, it is necessary to secure cuttings from healthy plants. Infected soils should be steam sterilized or treated with formaldehyde (see pp. 32-43). Spraying in this case will be useless since the causal organism works in the interior of the roots and stems. Root Knot (fig. 40, b), see Nematode, p. 28. Aspidistra {Aspidistra Lurida) Cultural Considerations. This plant is very easy to grow. It is valued mostly as a foliage plant. It grows well in dark halls and in dwelling houses. The plant reqiiires an abundance of water. It is propagated by division of rhizomes in late winter. Diseases of Aspidistra The Aspidistra is a very hardy plant. It is sub- ject to the attacks of but few diseases. Anthracnose Caused by Colletotrichum omnivorum Hals. This disease causes irregular ragged dry spots on the leaves. The spores are sickle shaped, hyaline, one celled. The setse are black, elongate, and pointed. The disease may be kept in check by spraying with a standard fungicide. All infected material should be destroyed by fire. 2o6 Diseases of Greenhouse Crops Leaf Spot Caused by Ascochyta aspidistra Mas. This disease is characterized by roundish, whit- ish spots on the leaves. The trouble is as yet of no economic importance. Little is known of the causal organisms. Of the other fungi recorded on aspidis- tra may be mentioned Fyrenochteta bergevini Roll. CHAPTER 18 ASTER (Aster sp.) Cultural Considerations, see Chrysanthemum, p. 235- Diseases of the Aster Although considered a hardy plant, asters are sub- ject to some important diseases when grown under greenhouse conditions. Yellows Cause, phjrsiological. Symptoms. This is a very obscure disease, the cause of which is little understood. It has been in- vestigated by Smith,* who, however, reached no definite conclusions. The roots of affected plants are apparently normal in every respect. The stems and branches, however, become pale yellow, slender and spindly, and in extreme cases stunted. The leaves too are often stunted and poorly developed. The flower bracts show no change, the cal)^ (se- pals) has a tendency to revert to leaf -like lobes. The color of the corolla changes to a uniform light greenish yellow irrespective of the original color of • Smith, R. E., Mass. (Hatch) Agr. Expt. Sta., Bui. 79: 3-26, 1902. 207 2o8 Diseases of Greenhouse Crops the variety. In form, the florets of the corolla be- come elongated, tubular, with short lobes at the ends. The stamens have a tendency to abort, the anthers are undersized, producing little or no pol- len. The pistil tends to elongate, the stigma too becomes much elongated and enlarged, protruding abnormally from the corolla tube. The ovary and ovules too are elongated and enlarged (fig. 42, a and b). Affected plants produce no seeds. The same disease also attacks the Marguerite, the Calendula, and the African Marigold. The cause of the trouble is unknown. Practically all varieties of asters are equally susceptible. The source of the seed, its stor- age conditions, transplanting, the ph3^ical proper- ties of the soil, are not apparently concerned in the development of this malady. Control. It is very likely that yellows may have an origin similar to that of mosaic. In the latter case, insects are likely to carry and to spread the virus. The control of all insect pests is therefore recommended. Diseased plants should be pulled out and destroyed by fire. Spraying will be of no benefit. Leaf Blight Caused by Bacillus asteracearum Pava. The disease is known to occur in Italy where it was described by Pavarino.* The trouble is ap- •Pavarino, G. L., Atti. R. Accad. Lencei Rend. CI. Sci. Fis, Mat. et Nat. 21 : 544-546, 1912. Fig. 42. Aster Diseases. a. Blossoms affected with yellows, notice the one-sidedness of the petals, b. section of a partially diseased blossom, showing upward turn of affected florets, c. young plant affected with Fusarium wilt (a-c after Smith, R. E.). Aster Diseases 209 parently confined to the foliage, the lower leaves usually becoming infected first, then dry and shrivel. Leaf blight is as yet of no importance in this coun- try. Wilt or Stem Rot Caused by Fusarium sp. Symptoms. This disease appears as soon as the plants are set out and persists throughout the grow- ing season. It is, however, most noticeable during planting time and at blossoming. The trouble usu- ally becomes apparent first on the lower leaves. Here the normal color disappears, turning to a dull yellowish green, followed by wilting. This seems to spread throughout the length of the stem although the disease is usually confined to one side of the plant (fig. 42, c). This gives it a very characteris- tic appearance, since one side of the plant has a dull-green, wilted, blighted appearance and only one half of some of the leaves and flowers are af- fected at first. When pulled up, the roots and stems of a diseased plant appear perfectly healthy. However, if one splits open lengthwise the stem of an infected plant, he will find that the seat of the trouble is localized in the interior of the woody or vascular tissue, the latter of which will be darkened. Infection in this case no doubt takes place in the seed, at the seedling stage. Although some plants are able to make a little headway in spite of the dis- ease they too finally succumb. The cause of the 210 Diseases of Greenhouse Crops trouble is a Fusarium fungus, of which little is now known. Control. Since the Fusarium fungus is a soil in- habiting organism, steam sterilization of the soil at once suggests itself. The seed should always be started on a sterilized soil, and this trouble will be entirely eliminated. Diseased plants should be pulled out and burned, and by no means allowed to find their way into the manure pile. Spraying in this case will be of no value, since the seat of the trouble is confined to the interior of the roots and stems. Other Troubles Mistaken for Wilt. An injury in- flicted by the common white grub (Lachnostema) is often mistaken for wilt. The latter feeds on the roots, and the result is a general wilting. When the aflEected plant is pulled up, the grubs will be foimd in the act of feeding. By careful watching, they may be destroyed before serious damage results to the plants. Another cause of apparent wilt and stimted growth may be due to the sucking of the root lice. The latter are of a bluish color, and are usually foimd in large number on a single plant. This pest usually is harbored in the soil, especially where as- ters are continually grown in the same beds. Chang- ing the soil or sterilizing it with steam will eflFect a cure. In Europe, Fusarium incamatum (Desm.) Sacc. is believed to be the cause of an aster wilt there. Aster Diseases 211 Damping Off Caused by Rhizoctonia solani Kuhn. Symptoms. The trouble is at first manifested as brownish spots on one side of the seedlings at the surface of the soil. The lesions increase in size until the seedlings are girdled and topple over. In time, the Rhizoctonia fungus spreads over the fallen plants and forms a mat of mycelia over them. On older aster plants, a damping off is not pro- duced, but instead the typical Rhizoctonia lesions appear on the stem end and on the roots. For a description of the causal organism and methods of control, see p. 20. Root Knot Caused by Heterodera radicicola Muhler. Symptoms. The disease manifests itself when the plants are about three inches high. The younger portions of the plant produce spindly shoots with dwarfed, disfigured leaves. The color of this growth is yellowish pale to white, the flowers are small and stunted. Such plants are known to florists as "white legs." For a description of the organism and meth- ods of control see Nematode, p. 28. Azalea {Azalea Indica) Cultural Considerations. Azaleas are very sensitive as regards water. They require plenty of moisture. 212 Diseases of Greenhouse Crops but not so much as to make the soil soggy. They demand a cool, shady house and a rather close at- mosphere. The varieties forced for the Easter mar- ket should be kept in a temperature of 45 to 50 de- grees F., and those forced for Christmas should be grown under a temperature of 50 to ^^ degrees. Six to eight weeks before Christmas the plants are given a temperature of 60 to 65 degrees F. In providing ventilation, cold drafts should be avoided. The best time to re-pot azaleas is after blooming. Neglect in this direction may seriously interfere with next year's bloom. Azaleas are very sensitive and may be injured even by the presence of organic matter of a heat producing nature. This means that the ma- nure in the compost must be thoroughly rotted. Diseases of Azalea The literature on azalea diseases is very scant. This means either that the troubles of this plant are still to be investigated or that it is a remarkably healthy one. Leaf Spot Caused by Septoria Azalee Vogl. Symptoms. This disease is characterized by red- dish yellow spots on the leaves. It is not of great importance economically. The Organism. The pycnidia are immersed, glo- bose, depressed, black. The conidia are oblong, fili- form, straight or curved, 1 to 3 or more septate, and Fig. 43. Begonia Root Knot. Begonia Diseases 213 constricted slightly at the septum. The Conidio- phores are short and cylindric. The Begonia (Begonia sp.) Cultural Considerations. Begonias have become a very popular plant commercially. The tuberous type is extensively grown imder glass. Throughout the season, the plants require frequent applications of liquid cow manure. They require an abundance of light and air, but are very sensitive to draughts and to exposure to direct sunlight. The best tem- perature required is about 65 degrees F. In the summer, the house should be frequently syringed in order to keep it cool. Diseases of the Begonias Begonias, althou^ considered hardy plants, are subject to a few important diseases. Powdery Mildew Caused by Oidium sp. Stewart* records a powdery mildew attacking the stems but not the leaves of begonia. The trouble appears as a white powdery fungus growth charac- teristic of all similar mildews. Only the Oidiirai or conidial stage of the fungus is present. It is not •Stewart, F. C, New York (Geneva) Agr. Expt. Sta. Bui. 388: 33». '9JO- 214 Diseases of Greenhouse Crops likely that this disease will become troublesome in greenhouses where begonia is grown on a large scale. Root Rot Caused by Rhizoctonia solani Kuhn. The symptoms of root rot on begonia are the same as those described for alternanthera. The fim- gus also causes a damping off disease on young be- gonia cuttings. Root Knot (fig. 43), see Nematode, p. 28. Caladium {Caladium sp.') Cultural Considerations. Caladiums should never be allowed to become pot bound. They require a medium temperature, plenty of water, ventilation, and drainage. As the growing season is over and the plants lose their leaves, the pots should be laid on their sides and the water withheld sufficiently to prevent growth. Diseases of the Caladium Caladiums, it seems, are very hardy. The fungi recorded on matured parts of this plant may be men- tioned : Cercospora caladii Cke., Macrophoma surinamen- sis (B. and C.) Berl. and Vogl., Monilia prunosa Cke. and Mass.; Spherella caladii (Schw.) Sacc, Urotnyces caladii (Schew.) Farl. Fig. 44. CoLCEOLARiA Leaf Blight (After Halsted). Calceolaria Diseases 215 Calceolaria (^Calceolaria arachnoidea') Cultural Considerations. Calceolariae are green- house annuals grown for decorative purposes. It requires a soil made of equal parts of leaf mold, sand, and sand loam. The plants require frequent repotting to prevent them from becoming potbound, although the flowers are usually better when pot- bound. The plants require a northern exposure dur- ing the summer, plenty of ventilation, and a cool house. A temperature of 70 degrees F. may seri- ously injure them. Partial shading should be pro- vided, and no water should be permitted to accu- mulate on the foliage. Diseases of the Calceolaria The Calceolaria is apparently a very resistant plant. Halsted,* however, records a leaf blight that affects it. The trouble appears as brownish patches on the leaves just about blossoming time. The patches are many sided and seem to be bound by the smaller veins of the leaf (fig. 44). The spots are water-soaked, and transparent when held against any light. The cause of this trouble seems to be a bacterial organism which, however, needs further in- vestigation. The same is true for methods of con- trol. • Halsted, B. D., New Jersey Agr. Expt. Sta, 14th Ann. Kept.: 430-431, 1893. 2i6 Diseases of Greenhouse Crops Canna {Canna indicd) Cultural Considerations. The canna, although an outdoor plant, is also extensively grown in the green- house for propagation and for decoration. The va- rieties best adapted for forcing may be mentioned: Queen Charlotte, Madame Crazy, Explorateur. For flowering in the greenhouse it is best to start with dormant plants. Fungi Recorded on the Canna Carmas seem to be unusually free from diseases. With the exceptioi^ perhaps of the rust, Uredo can- na, the others here mentioned are saprophytes or semi-saprophytes attacking old and weakened plants. Anthostomella achira Speg., Macrosporium bul- botrichum Cke., Ophiobolus linosporoides Speg., Uredo canna Wint. CHAPTER 19 THE CARNATION {Dianthus caryophyllus) Cultural Considerations. The general trend of cultural operations in the greenhouse (fig. 45) should be toward the production of a healthy, vigorous growth. The cutting itself will, to a cer- tain extent, predetermine the health of the plant. Cuttings should not be weak to begin with. Those which are firm, but also somewhat soft, are desirable. The best cuttings are usually made from the strong pips along the sides of the stems. As soon as the cuttings have developed roots in the propagating bed, they are usually transplanted into pots or into flats. In either case, they should not be planted too deeply in the soil. Deeply set cuttings are more subject to stem rot, especially when overwatered. As the cuttings develop they should not be permit- ted to become pot bound. By keeping them in a comparatively low temperature, the formation of soft succulent growth will be prevented. With many growers, carnations are grown in the field for a time. This practically insures vigorous growth as it develops a certain hardiness and resistance to dis- ease. Where land is scarce, carnations are grown indoors in the summer. Such plants, however, are 217 2i8 Diseases of Greenhouse Crops found to be weak and susceptible to disease. In first pinching back the plants to encourage spreading, it should be done in such a way that the plants will branch some distance above the surface of the soil. In other words, the farther the stems are from the ground the more protected the plant is from disease. When the plants are permanently set for the winter, heavy watering should be avoided. Too much water compacts the soil, excludes air, and retards normal root development. As the plants become well es- tablished, and especially during the hot days of Sep- tember and October, as well as in the spring, they should not be permitted to suffer from a lack of water. This is especially true in raised benches with the heating pipes directly underneath. In this case, the surface soil may appear wet, yet the soil be- neath may be as dry as possible. On the other hand serious injury may occur from overwatering, espe- cially in solid benches on cloudy days. The night temperature of the carnation house should be about fifty degrees F. At sixty degrees the plants will be stimulated to slightly earlier blooming, but the blooms will be small, and the plant subject to a more rapid exhaustion. At a night temperature of 40 degrees F. blooming will undoubtedly be re- tarded although the plants will be stockier and last longer. The day temperature of the house should be decided upon according to outside weather condi- tions. On a clear day and when sufficient ventila- tion is given, the temperature may run from 65 to 75 degrees F. Carnation Diseases 219 Diseases of the Carnation White Tip Cause, gas injury. Symptoms. The trouble appears as a white or creamy coloring of the unrolled tender tips of the foliage (fig. 46, a). Occasionally, the white spots appear across the leaves a short distance below the tips. The cause of the injury is believed by Clin- ton* to be due to gas rather than to spray injury. The trouble may be brought about by the fumes of sulphur or tobacco used as an insecticide or fungi- cide. The injury affects the tip because of the ten- derness of the tissue there. The Enchantress is par- ticularly susceptible to it. The secret of its suc- cessful control lies in the care exercised during fumi- gation. Sleep Cause, gas injury. Growers in the vicinity of large manufacturing plants are often troubled with what is called sleep of carnation. This trouble is especially common in cities where gas is used for illumination. The symptom of sleep is a closing inward of the petals (opened corolla). Once a blossom goes to sleep it never opens again. The investigations by Crocker and Knight t have shown that at least one cause of sleep in carnation is due to traces of illuminating •Clinton, G. P., Conn. Agr. Expt. Sta., Thirty-ninth Ann. Rept.: 428-439, 1915- t Crocker, W., and Knight, L., Bot Gaz. 56:259-276, 1908. 220 Diseases of Greenhouse Crops gas (ethylene) in the surrounding atmosphere. This trouble has been overcome in floral establishments where lighting gas was replaced by electricity. Malnutrition Cause, overfeeding. Symptoms. The trouble is usually manifested on the blossoms. It is brought about by the applica- tion of an excess of certain chemical fertilizers. Acid phosphate applied in large quantities seems to produce no injury. An excess of dried blood will produce blossoms which become soft and subject to sianbum if sprinkled during sunshiny weather. Later, such injured blossoms have their center petals bunched, and only a few others opening. Later, the buds fail to open, the foliage assumes a deep green color with abimdant glossiness and a normal growth. If overfeeding is continued growth ceases. Plants thus aflEected may, however, recover with ju- dicious feeding. Overfeeding with potassium sulphate is decidedly unfavorable. The edges of the inner petals crinkle, brown spots appear, and often there is a withering of the edges of the petals, while the center ones fail to open, as though glued together. The unopened buds swell, and the pistil is commonly seen project- ing one inch beyond the bud. Moreover, there is a retarded growth, the leaf tips begin to die, and the whole plant resembles a rosette. Carnation Diseases 221 Splitting of Blossoms Cause, underfeeding. Carnation growers often lose heavily from the splitting of blossoms just before they fully open. The investigations of Darner* and others seem to show that the splitting is brought about by under- feeding. The moderate application of commercial fertilizers will not cause an increase in splitting and may cause a decrease. The splitting of the blossoms may also be noticed on the row of carnations near the glass of the side benches. The cause, it is assumed in this case, is due to the more rapid drying of the soil of the benches nearest the glass. Growers often prevent this trouble by so placing the benches as to allow a walk between them, and the side walls. Yellows Cause unknown. Symptoms. True yellows as described by Lam- key t appears as a yellowing (mottled chlorosis) on the leaves. The mottling is brought about by the presence of indefinite irregular blotches or flecks which meet and form yellow streaks. The mottling is more common on the younger leaves, and the streaks on the older ones. The yellow areas may becrane red or pink. The spots are never water- •Darner, H. B., et al., Illinois Agr. Sta. Bui. 176: 378-379i I9»4- t Lamkey, M. R., The American Flor. 58 : 508-510, 1917. 222 Diseases of Greenhouse Crops soaked and possess no watery margin. They are always sunken, and possess no definite center. The cause of the trouble does not seem to be associated with any parasitic organism, but is probably due to improper cultural conditions, the exact nature of which is imknown. Control. The control for yellows, as recom- mended by Peltier* is as follows : Every check which tends to lower the vitality of the plant should be avoided. Weaker plants are more subject to yellows than stronger ones. Cuttings should never be taken from plants showing yellows. They should be made, too, from plants in bloom rather than from stock plants. They should be rooted early and should not be permitted to remain too long in the sand after rooting. The later the cuttings are made, the longer they take to root, and the more susceptible they are to yellows. Young plants should not be allowed to become pot bound. Cohesion of Petals Cause unknown. Carnation growers are often troubled by what is generally termed cohesion of petals. The latter are well out of the caXyx., but are stuck together. Often they are grown together to such an extent that it is impossible to separate them without tearing the tissue. The trouble was first described by Arthur.t but the exact cause of it is as yet unknown. ♦Peltier, G. L., The American Flor. 46: 725-726, 1906 t Arthur, J. C, Froc. Amer. Carnation Soc., 1896. Fig. 46. Carnation Diseasbs. a. White tip (after Clinton), b-f. carnation rust parasite (after Blodgett, F. H.), g. stigmanose (after Woods), h. Septoria leaf spot (after Potter, M. C), »• pycnidia of Septoria dianthi, j. pow- dery mildew fungus (after Mercer, W. B.). Carnation Diseases 223 Stiomonose Caused by insect sting. Symptoms. The best symptoms of this disease are manifested on the younger, but full-sized leaves nearest the upper end of the stem. A casual glance at such leaves reveals little to the untrained eye. However, by holding them near the sunlight, small dots may be seen scattered. These dots have a faint yellowish color. Later the surface tissue dries and the dots assume a whitish, reddish, or purplish color, while the spots enlarge and become sunken (fig. 46, g.). Such spots are seldom dark colored in the center nor are they made up of concentric rings. With the increase of the spots, the leaves wither, but cling to the stems. The general effect of stigmonose is a premature yellowing and stunt- ing of the plant. The vigor of the plant at the time of the appearance of the disease largely determines the severity of the injury. Strong plants will be- come spotted, but will in no other way greatly suffer from it. Weak plants of the same variety will be- come stunted, and in many cases seldom outgrow the disease. The cause of the disease was first attributed by Arthur and Bolley* to a bacterial organism Bac- terium dianthi Arthur and Bolley. However, the investigations of Woods t show that stigmonose is •Arthur, J. C, and BoU^y, H. L., Indiana Agr. Expt. Sta. Bui. 59: 17-3S, 1896. t Woods, A. F., U. S. DepL of Agr. Div. of Veg. Pathl. and Phy», Bui. 19: 7-30, 1900. 224 Diseases of Greenhouse Crops caused by the stings of aphides, thrips, and red spiders. The irritant injected by these pests causes the cells to react and finally to collapse, resulting in the specking previously mentioned. Control. The carnation is a plant which is nat- urally adapted to a dry atmosphere. Under such conditions in the greenhouse aphides, thrips and red spiders are at their maximum activity. To keep these pests in check fumigation with tobacco ex- tracts or hydrocyanic acid gas is resorted to. The use of the latter, however, cannot be recommended for all carnation varieties. Rust Caused by Uromyces caryophyllinus (Schrank) Wint. Symptoms. The rust is readily recognized by ele- vated blisters or sori filled with brown spores. The sori are first covered by the epidermis of the host, but when they ripen the latter bursts open, liberat- ing the mature spores. This disease is more prev- alent in overheated and overwatered houses. In- fection once established will usually destroy a large per cent of the plants and seriously cripple many others. The disease may be found on all parts of the plant except the roots. Carnation rust seems to be more prevalent in the states lying east of the AUeghenies, Few greenhouses seem to be entirely free from the rust. The Organism. The fungus has two spore stages, Carnation Diseases 225 the uredospores and teliospores, both of which forms greatly resemble each other. The iEcia are found on Euphorbia gerardiana in Europe and is recog- nized as Mcidium euphorhie-gerardiane Fisch. The rust fungus attacks not only the carnation, but sev- eral other species of the pink family. Control. Some florists advocate the use of an aqueous solution of common table salt. This is to be applied as a fine spray. Investigations by F. C. Stewart* have shown that salt solutions can neither prevent rust infection nor stimulate growth. Neither is it helpful to apply salt to the soil. Carnations are propagated chiefly by cuttings. The latter often carry the disease. It is, therefore, imperative that cuttings be taken from healthy plants. Maintain- ing the proper temperature and ventilation, as well as exercising care and judgment in watering, will help to keep this rust in check. Subirrigation is preferred to overhead irrigation to keep the plants dry. Progressive growers use an inverted V-shaped wire netting (one-inch mesh) placed between the rows. The wire is cut into strips of fifteen inches width. These are bent and inverted, about six inches high and eight inches wide, and placed between the rows of plants. This support to the foliage pre- vents it from touching the wet ground and admits at the same time perfect ventilation. It also makes it possible to water the soil without wetting the plants. The trouble may, of course, be avoided to 'Stewart, P. C, New York (Geneya) Agr. Expt. Sta^ i6tli Ann. Rept.: 423-425, 1895. 326 Diseases of Greenhouse Crops a great degree by growing resistant varieties. The Scott and the Jubilee are two varieties very sus- ceptible to rust. On the other hand, the Enchantress and the Lawson are highly resistant, A Parasite of Carnation Rust. Most parasites have others to live on them. The carnation rust seems to be no exception. The fungus Darluca filum (Bin.) Cast, was found by Blodgett* to para- sitize the carnation rust fungus. The presence of the Darluca is manifested by a dwarfed and weak development of the rust pustules. The pycnidia of Darluca (fig. 46, b and c) are found scattered on the rust pustules and are flask shaped, the spores are two-celled (fig. 46, e and f), colorless, and when ripe escape in masses of long tendrils, held together by a gelatinous substance in the outer cell wall of the spore (fig. 46, d.). The latter readily germinate in water. Darluca filum also attacks the asparagus rust fungus. It is possible to grow Darluca in pure culture and to inoculate its spores on the carnation rust fungus. In nature, however, it has not proved abundant enough to keep the rust in check. Septoria Leaf Spot Caused by Septoria dianthi Desm. Symptoms. Leaf spot is characterized by light brown patches on the leaves and stems. On the latter, the spots are usually found midway between •Blodgett, F. H., New York (Geneva) Agr. Expt. Sta., Bui. 175: 1-13, 1900. F"iG 47. Carnation Diseases. a. Healthy blossoms, b. blossoms affected with Sporotrichum rot (after Stewart, F. S. and Hodekins), c. Heterosporium spot (after Smith, R. £.), e-d. Alternaria spot (after Stevens and Hall). Carnation Diseases 227 the joints. On the leaves, infection seems to be more localized on the lower than on the upper half, and it is particularly frequent on the broad sheath- ing base of the leaf (fig. 46, h.). Affected foliage is often bent downwards. A leaf with numerous spots may be bent at various places, downward as well as sideways. The spots are usually indefinite in size and outline. Within the dead area may be found numerous minute fruiting bodies (pycnidia). Powdery Mildew Caused by Oidium sp. Mention of this disease is made by Mercer,* who found it on, greenhouse carnations in England. It has not yet proved of economic importance in the United States. This trouble appears as white, pow- dery patches on the leaves, calyx, and corolla. The English varieties most susceptible are "Lady Arling- ton," "Bridesmaid," and especially "British Tri- umph." So far only the conidial or Oidium (fig. 46, g) stage of the fungus is in evidence. The ascus or winter spore stage may probably appear on other hosts. The trouble may be kept in check by dust- ing with flowers of sulphur or by spraying with potassium sulphide as recommended for the rose mildew (see p. 323). 'Mercer, W. B., Jour. Roy. Hort. Soc. 41 : 227-229, X915. 228 Diseases of Greenhouse Crops Bud Rot Caused by Sporothrichum poe Pk. Symptoms. This disease seems to be confined to the floral buds only. Ordinarily the affected buds fail to expand or only open part way (fig. 47, a and b.). A close examination will show that the interior of the affected bud is browned and moldy. The rotted tissue may be found in the center of the bloom or on the petals. The stamens, styles, and pistils are also frequently affected. Where yoimg buds are diseased the calyx, too, will be involved, otherwise it is usually sound, although the other parts of the flower may be decayed. The Organism. The hyphse are creeping, vary- ing in thickness, hyaline, and septate. The conidia are of two kinds: Microconidia — one-celled, globose or broadly ovate; Macroconidia — abimdant, one, rarely two, septate and several times larger than the microconidia (fig. 48, g to i.). Stewart* claims that Sporotrichum pocz Peck found on diseased tops of June grass and S. anthophilum, which causes the bud rot of carnations are the same. The fungus is spread about in the greenhouse by a mite {Pedicu- lopsis graminum Reut.). Control. According to Heald t and others the most susceptible varieties to bud rot may be men- tioned — the Lawson, Enchantress, Queen Louise, • Stewart, F. C, and Hodgkiss, H. E., New York (Geneva) Agr. Expt. Sta. Tech. Bui. 7: 84-119, 1908. t Heald, F. D., Nebraska Agr. Expt. Sta., Bui. 103:3-31, 1908. Fig. 48. Carnation Diseases. a. Mycelium of Alternaria dianthi showing branching and septation, b. mycelium below stroma and hyphes emerging through the stroma, c. caten- ulate spores as borne upon hypheXj d. spores, e, an old cluster of conidio- phores, /. a young cluster of comdiophores (after Stevens and Hall) , g. hyphex of Sporotrichum poae with immature spores on short tapering branches, h. typical spores of S. poae, «. germinating spore, /. Fusarium like spores of S poae, k. carnation blossom rotted, showing cg§s of mites, I. female mite, m. male mite (after Stewart, F. C, and Hodgkiss, H. E.). Carnation Diseases 229 and Bradt. These, therefore, should be handled with more care. All diseased buds should be picked oflF and destroyed by fire. The temperature and moisture in the air should be kept as low as possi- ble. The fact that the mite which is associated with bud rot (fig. 48, k to m) is also found on June grass would suggest the necessity of avoiding sod where this grass is common, in the making of the compost. This, however, may not be important when the soil is steam sterilized. Leaf Mold Caused by Heterosporium eckinulatum Berk. Symptoms. The disease becomes apparent as roundish spots, varying from a sixteenth to a sixth of an inch in diameter, and is found mostly on the tip of the leaves. In severe cases the entire leaf and even the major tops of the plant become spotted (fig. 47, c). According to Halsted* the color of the spots is pale ashy and covered with a fine, dense growth of the causal fungus, giving it the moldy ap- pearance. Frequently the color changes to a gray shade, sometimes approaching dark brown. Alternaria Leaf Spot Caused by Alternaria dianthi Stevens and Hall. Symptoms. This trouble manifests itself as ashen 'Halsted, B. D., New Jersey Agr. Expt Sta., Fourteenth Ann. Kept: 386, 1893. 230 Diseases of Greenhouse Crops white spots, the centers of which are occupied by a scanty or profuse black fungus growth, which is made up of the spores of the fungus (fig. 47, d and e.). The spots are dry, rather shrunken, circu- lar or somewhat elongated. If the node of the stem is attacked, the disease spreads sufficiently to involve the adjoining foliage as well. The stem itself be- comes somewhat girdled and in time is also killed. Usually, however, the spots are confined to the foliage. The Organism. The mycelium is dark brown, (fig. 48, a.). The conidiophores arise from a stroma, usually from one to twenty-five in number, and each one to four septate (fig. 48, b, e and f.). The coni- dia are borne in chains (fig. 48, d.), and in structure are very typical of other Altemarias (fig. 48, d.). The fungus grows well on various culture media. On media poor in sugars, the mycelium and spores are lighter in color and smaller in size and diameter. Control. All infected material should be collected and destroyed by fire. Spraying with a standard fungicide is also recommended. From the observa- tions of Stevens and Hall,* the variety Mrs. Thomas W. Lawson appears to be the most susceptible to this disease. As far as possible, this variety should be avoided. Anthracnose Caused by Volutella sp. Symptoms. The disease usually attacks the base * Stevens, F. L., and Hall, J. G., Bot. Gaz. 47:409-413, 1909. Carnation Diseases 231 of the lower leaves as well as the stems which are closest to the ground. The trouble is seldom foimd on the upper leaves, although they may present a sickly pale appearance. Anthracnose is a serious disease of young cuttings. Not infrequently the grower loses 50 per cent of his cuttings from this disease. These damp off very quickly under a great variety of conditions. Damping Off Caused by Volutella leucofricha Atkinson. This disease seems to be confined mainly to carna- tion cuttings. The symptoms are not different from those of the damping off caused by other fungi. In this case, the causal organism, Volutella leucotricha, first described by Atkinson,* is distinct from V. dianthi Hals. The mycelium of the former has a tendency to swell a^ the hjrphal cells, producing a strong constriction at the septa. The conidia of Volutella leucotricha are considerably smaller than those of V. dianthi and the setse are different in form and in color. In V. leucothrica they taper but little towards the free end, are blunt at the tip and many times septate, with the stroma light colored, while it is black in V- dianthi. The methods of control are the same as those for other damping off diseases (see p. 17). •Atkinson, G. F, New York (Cornell) Agr. ExpL Sta. Bui. 94: 260-264, 1895. 232 Diseases of Greenhouse Crops FusARiuM Leaf Spot Caused by Fusarium sp. Symptoms. This form of leaf spot usually fol- lows the injury caused by the rust fungus (Uromyces caryophyllinus). The variety Emily Pierson is es- pecially subject to the attacks of this peculiar leaf spot. The spots are large, often occupying the en- tire width of the leaf. The diseased tissue becomes covered with a pinkish mold in the center of which are found minute spore clusters of the Fusarium fun- gus. Little is known of the causal organism. In controlling rust, the leaf spot will also be kept in check. 'Branch Rot," Dry Stem Rot, or Die Back Caused by Fusarium sp. Symptoms. This troublesome carnation disease was first described by Sturgis.* Attacked stems and branches wilt rapidly and the color of the leaves turns to a yellowish green. Dead stems remain firm, although wilted and shriveled. The bark likewise remains firm. The causal fungus seems to gain entrance through cuts or wounds. With cuttings the trouble may start at the base, causing them to dry up and to lose their normal color. The condi- tions which favor the disease are excessive rains in the summer when the plants grow out of doors. This favors a large, bushy, soft growth, with a 'Sturgis, W. C, Conn. Agr. Ezpt. Sta., Kept. 2x: 175-181, 1898. Carnation Diseases 233 consequently profuse topping, which opens the way to the disease. Control. Peltier* recommends the use of medium sized sturdy plants in preference to large, bushy ones. As much as possible, overcrowding should be avoided. During the first three months after the plants have been brought in, the temperature should be kept as low as the plant will tolerate. The syringing should never be given in the evening nor in the cloudy weather. It should be given on clear days in the morning so that the plants will be dry by the evening. In topping a plant, care should be taken to make clean cuts and to avoid leaving stubs. In gathering flowers, break them off at a node. Finally all diseased material should be pulled out and destroyed by fire. Root Rot Caused by Rhizoctonia solani Kuhn. Symptoms. The disease is at first manifested by a yellowing of the affected plant or branch. A few days later actual wilting takes place. This is true only in sunny weather. During cloudy weather, the plant remains turgescent even though the stem may be badly rotted. The trouble is confined to the stem end or to the roots of the plants. Deep brown lesions usually precede the rot and indicate the places where infection started. High tempera- tures and deep planting favor the disease. Of the •Peltier, G. L., The Amer. Flor. 56: 725-7*6, ig'*- 234 Diseases of Greenhouse Crops older varieties, the following are reported as being especially susceptible to stem rot: Crimson King, Scott, Jubilee, La Purite, De Graws, Servan, Silver Spray, Flora Hill, McGowan, Portias, Boston Mar- ket, Craig, Lawson, Winson, and Lady Bountiful. The newer varieties do not seem to possess any more resistance than the older ones. For a description of the causal organism and methods of control, see p. 20. Root Knot Caused by Heterodera radicicola (Greef ) Muller. Symptoms. Root knot is characterized by swell- ings of the roots. Affected plants are decidedly dwarfed, yellowish, and sickly looking. The roots of diseased plants are extensively knotted, and lumpy. For a description of the causal organism and of methods of control, see p. 28. o o X s « (-1 z < X u H CHAPTER 20 THE CHRYSANTHEMUM {Chrysanthemum sp.) Cultural Considerations. Chrysanthemum cut- tings should be thick, firm, have several joints, and be about three inches in length. If the cuttings within three weeks fail to make a good root system, they should be discarded as weak stock. A house temperature of 50 degrees F. and a bottom heat of 60 degrees is best suited for the cuttings. It is very unwise to allow the cuttings to remain in the propa- gating bed as soon as they start to grow. In trans- planting for the first time the soil should not be too rich. A good loam with very little rotted manure is all that is required by the newly rooted cuttings. As the plants are finally set in benches in the green- house (fig. 49) they need a rich soil, as they are heavy feeders. The benches need not be over five inches, the depth of the soil not over four inches. As the plants are first set out in the benches, it is advisable to water only around each plant. As they become well established the entire bed may be watered with safety. It should be borne in mind that the soil must be kept moist very uniformly. Sudden drying of the soil checks growth, and too much will cause the leaves to become yellow and sickly. On bright days, syringing the foliage is 235 236 Diseases of Greenhouse Crops very helpful. This, however, should be done in the early part of the day, so that the foliage will be dry at night. Chrysanthemums are heavy feeders, and this should not be lost sight of. Diseases of Chrysanthemums Chrysanthemums are subject to several important diseases. These often become so troublesome as to seriously interfere with the profitable culture of the plant. Crown Gall Caused by Pseudomonas tumefaciens Ew. Sm. This disease causes swellings on the crown and the roots of the plant. The trouble is seldom of any economic importance under greenhouse conditions. The causal organism attacks not only chrysanthe- mum, but also the daisy, geranium, sugar beet, pop- lar, willow, peach, etc. Black Speck Caused by Pilobolus crystallinus (Wigg.) Tode. The speck is often found on the leaves. Some growers believe this specking due to the accumu- lation of smoke settled on the leaves after fumiga- tion. Others believe that it is due to a con- densation of ammonia arising from fresh manure. As stated for a similar case on roses (see p. 321), the specking is due to the discharge of sporangia of Fig. so. Chrysanthemum Diseases. a. Botrytis blossom rot, healthy and diseased (after Spaulding), b. ray blight (after Stevens, F. L.), c. chrysanthemum rust (after Smith. R. E.). d. Urc- dospores of Puccinia chrysanthemi, e. Cylindrosporium fungus, /. Cylindro- sporium blight (e and f after Halsted). Chrysanthemum Diseases 237 Pilobalus crystallinus. The spore-bearing stalks of this fungus are possessed with a mechanism which throws off the ripe spores considerable distances. Being covered with a sticky substance, these spore masses readily adhere to anything standing in the way. The specking may be expected wherever manure is used as a mulch. According to Craig* the trouble may be promptly stopped by a light ap- plication of air-slaked lime. Rust Caused by Fuccinia chrysanthemi Rozc. Symptoms. Rust may be readily distinguished frwn all other diseases of the chrysanthemums. It appears as tiny, rusty blisters the size of a pinhead. When several appear together the blister assumes a larger size (fig. 50, c). At first, the blister is covered by the epidermis of the leaf. With age, however, the epidermis bursts and breaks away, ex- posing a brown powder which is made up of mil- lions of spores of the rust fungus. On badly in- fected plants, the leaves may be all covered with the rust sori which nearly always appear on the underside of the leaf. It was previously believed that the rust of chrysanthemum was the same which attacks common weeds bielonging to the same cran- positse family as the chrysanthemum. However, the investigations of Arthur t have definitely shown that 'Craig, J., Canada Expt Farms Repts., 1897: 91-133, 1898. t Arthur, J. C, Indiana Agr. Expt. Sta. Bui. 85: i43-i50> 190O' 238 Diseases of Greenhouse Crops the chrysanthemum rust attacks this plant and no other host. Uredospores from dandelions, burdock, ox-eye daisy, when sown on the chrysanthemum failed to produce the rust. On the other hand, ure- dospores taken from the chrysanthemum and sown on chrysanthemum hosts reproduce the disease. The disease no doubt is brought in with infected plants, or cuttings made from a rusted plant. The Organism. It is very strange that the uredo- spore stage (fig. 50, d) is the only stage of the chrysanthemum rust that is found in the United States. This makes the fungus short lived unless it is continually transmitted from living chrysanthe- mum leaves to others. The uredospores are spheri- cal to pyriform, possessing a spiny membrane and three germ pores. The teleutospores were mentioned and figured by Massee * and by Roze.f However, without making cultures it is doubtful whether these claims can be accepted as final. Control. It is claimed that the variety Queen is very susceptible to rust. It is also believed that pot- grown plants are less resistant to rust than are plants growing in benches. Hand picking, selecting of clean, strong stock, and inside culture are recom- mended to keep the rust in check. The chrysanthe- mum rust, although serious, need not be feared by the careful grower who selects his stock and who is careful about the watering and the ventilation of the house. *Mas9ee, G., Gard. Chron. 24: 269, 1898. tRoze. Bui. Soc. Myc. de France 17:88, 1900. Chrysanthemum Diseases 239 LiGuLE Rot Caused by Sclerotinia fuckeliana (De By) Fckl. This rot in which the ligules become involved is often mistaken for a heart rot, and a destruction of the receptacle. The latter disease is brought about by nutritional disturbances. Ligule rot is caused by the fungus, Botrytis cinera, the fruiting summer stage of Sclerotinia fuckeliana. Control. For ligule rot Crepin* recommends that the flower buds be sprinkled with a solution made up of two grams of chemically pure nitric acid to a liter of water. Blossom Rot Caused by Sclerotinia fuckeliana (De By) Fckl. Symptoms. This disease is usually confined to the blossoms only. The trouble first appears as minute discolored watery spots on the petals, giv- ing the latter the appearance of having been pricked with a needle. The white-flowered varieties show the spotting more distinctly than the colored ones. The spots rapidly enlarge and involve the entire corolla,. Diseased petals wilt, and are soon covered by a grayish, velvety growth (fig. 50, a), consist- ing of the summer fruit (Botrytis). After the first few flowers become affected, the trouble spreads •Crepin, H., Jour. Soc. Nat. Hort. France 11:53-59, 1910. 240 Diseases of Greenhouse Crops rapidly and causes great damage. According to Spaulding* no one variety or color of chrysanthe- mum showed any difference in resistance. Besides chrysanthemums the disease also attacks poinsettias (Euphorbia pulcherina). In this case the projecting angles on either side of the leaf be- come affected. It seems that with poinsettias, infec- tion is localized in the broad green leaves which grow along the stems below the red zones. At the place of infection there is an exudation of small white drops of the hardened juice along the larger veins. These hardened drops of juice on the dead spots are very characteristic of the disease on poin- settias. Infected leaves drop off prematurely, thus marring the appearance of the plant. About two days after infection, the characteristic fruiting of the fungus makes its appearance. Phyllosticta Leaf Spot Caused by Phyllosticta chrysantkemi E. and D. Symptoms. The spots are orbicular, purplish brown with a distinct border. The trouble is mostly confined to the leaves. Little is known as yet of the causal organism. It is probable that spraying with a standard fimgicide will control the trouble. * Spaulding, P., Missouri Botanical Garden, Twenty-first Ann. Rept: 185-188, i9za Chrysanthemum Diseases 241 Ray Blight Caused by Ascochyta chrysanthemi Stevens. Symptoms. This disease attacks the buds or the opened blossoms. The affected blossom becomes brownish, straw colored, and withers. The discolor- ation nearly always begins at the base and works up to the tip of the blossom. Affected buds fail to open altogether. On opened flowers, the disease attacks on one side so that the rays in that direction will become destroyed (fig. 50, b.). The receptacle and the peduncle of diseased blossoms turn black and become shriveled. Portions of the stem may also be attacked, turn black and girdled. The Organism. Ascochyta chrysanthemi was first described by Stevens.* The pycnidia are few, oc- cur singly or scattered about, and open by means of a short central ostiole. The spores are oblong, straight or irregular, hyaline, one septate, the ends obtuse or acute. Control. All diseased material should be de- stroyed by fire. Careful and frequent spraying will control the disease. Septoria Leaf Spot Caused by Septoria chrysanthemi Cav., and S. chrysanthemella (Cav.) Sacc. Symptoms. This disease usually appears as small 'Stevens, F. L., Bot Gaz. 44: 241-258, 1907, 242 Diseases of Greenhouse Crops dark brown spots which increase in size until they meet. Affected foliage drop off prematurely. Dis- eased plants become weakened and produce small flowers. The disease is often introduced in the greenhouse with infected cuttings. The pycnidia of the fungus are minute, while the conidia are ob- scurely septate. Control. Cuttings should be secured from healthy plants. All diseased leaves and trash should be de- stroyed by fire. Spraying with a standard fungicide is also recommended. Blight Caused by Cylindrosporium chrysanthemi E. & D. Symptoms. This disease seems to work quickly and affected plants are short lived. The trouble appears on the leaves as dark blotches about one- half of an inch to three-quarters of an inch in diameter. The spore heaps are formed on the dead tissue where the spots occur. The area beyond the spot turns yellow, and soon the leaves shrivel, droop, and cling to the stems (fig. 50, f.). The Organism. The acervuli of this fungus are imbedded, the conidia are somewhat thick but taper to the end; they are several septate and straight (fig. 50, e.). Control. Infected material should be destroyed by fire. Spraying with a standard fun^cide will protect the healthy plants. Chrysanthemum Diseases 243 Powdery Mildew Caused by Oidium chrysanthemi Robh. This is a very common trouble of indoor chr3rs- anthemums. Affected leaves become covered with a powdery white growth. It seems that the Oidium or summer stage is the only one that occurs on af- fected plants. The winter or ascus stage has not yet been recorded. The trouble may be controlled in the same way as the rose mildew (see p. 323). Some growers prefer to use sulphur by mixing it with an oil and applying it to the steam pipes as a paint. Cineraria (^Cineraria cruentct) Cultural Considerations. The culture of this plant is very simple. However, it should be kept in mind that it is injured by hot dry air and sensi- tive to slight frost. The plant should be syringed practically every day, winter or summer. It also requires a cool shaded part in the house. Fungi Recorded on the Cineraria The Cineraria, it seems, is very hardy. The fol- lowing fungi have been found on weakened or dead parts of the plant: Mcidium cineraria Rosti, Asco- chyta fibricola Sacc, Coleosporium sonchi (Pers.) Lev., Leptosphsria vagahunda Sacc, Puccinia erio- phore Thum. 244 Diseases of Greenhouse Crops Clematis Cultural Considerations same as Cyclamen, p. 248. Diseases of the Clematis Clematis is a hardy plant. In the greenhouse it is subject to but few diseases. Anthracnose Caused by Gloeosporiutn cletnatidis Sor. This disease was first met with by Sorauer * on Clematis Jackmanni in Gennany. It is not known whether this disease is present in the United States. Its introduction into this country should be carefully guarded against. Little is known of the causal or- ganism. The disease may be kept in check by the destruction of diseased material. Leaf Spot Caused by Cylindrosporium cletnatidis E. and E. This trouble is manifested as reddish brown sub- angular to roundish spots on the leaves. The acer- vuli arc immersed, scattered and few in numbers. The conidia are somewhat curved and when ripe exude in a white mass. C. clematidis, var. Jack- manni E. and E., also found on the clematis, dif- fers from the former in the acervuli exuding a *Sorauer P., Ztschr, Pflanzenkrank. 7: 230, 1897. Fig. 51. Broom Rape of Coleus (After Halsted). Coleus Diseases 245 black mass of spores which are hyaline when looked at individually. Coleus Cultural Considerations same as Geranium, p. 260. Diseases of the Coleus Coleus is an imusual hardy plant in the sense that it is subject to so few diseases. Damping Off Caused by Rhizoctonia solani Kuhn. It seems that the variegated green varieties are more susceptible to damping ofF than the variegated red and yellow. Infected cuttings show lesions at the stem and above the surface of the soil. As the lesions spread and work in deeper in the tissue, the cutting topples over. For a description of the causal organism and methods of control, see p. 20. Broom Rape Caused by Orobanche ramosa L. Coleus is often subject to the attacks of a broom rape (fig. 51). The trouble was found by Hal- sted and Kelsey * on greenhouse plants. Orobanche, the broom rape genus, is of interest to greenhouse growers, because of its parasitic nature. Broom rape * Halsted, B. D., and Kelsey, J. A., Nevr Jersey Agr. Expt. Sta., 23rd Ann. Kept.: 408, 1902. 246 Diseases of Greenhouse Crops is a degenerate flowering plant. According to Harsh- berger,* the embryo of OrobanchjE has no trace of root and stem, but it consists of a spiral filament of delicate cells which feeds on the stored reserved food of the seed. Upon coming in contact with the roots of a suitable host it adheres itself closely and swells considerably, assuming a flask-shaped appearance. Secondary filaments are now produced from the flask-shaped body which bore in and penetrate into the vascular system of the roots of its host, where it receives its food. At the point of union between host and parasite, a bud is formed which later de- velops into a thick flower bearing stem which grows out above ground. The Croton {Codieum variegatum) Cultural Considerations. Care should be taken -.jt to allow the plants to become pot bound. The best foliage color is obtained when exposed to full sunlight. The plants do well in a moist house with frequent syringing of the foliage. The tempera- ture at night should never be permitted to go down below 70 degrees. Diseases of the Croton The Croton is considered a very hardy plant, but one disease is of importance to the greenhouse man. * Harshberger, J. W., A text book of mycology and plant path- ology: 299, 1918. P. Blakiston's Son & Co., Philadelphia, Pa. Croton Diseases 247 Anthracnose Caused by Glceosporium soraurianum All. Symptoms. This disease is manifested as large yellowish-gray spots on the leaves, which become whitish, dry and brittle with age. The spots are more visible on the upper part, although they work down through the entire thickness of the leaf. The acervuli are usually formed within the spots and become apparent as salmon-colored, gelatinized dots. The causal organism resembles other Glceosporium in structure. G. soraurianum is probably the same as G. crotonis Del., also found to attack croton leaves. CowJYLiNE \Cordyline aus trans') Cultural Considerations. This plant greatly re- sembles dracenas. Cordylines are usually grown in pots. They require a warm moist atmosphere, and are sensitive to full light. However, during the fall they should be kept drier, and exposed to full light in order to better bring out the color of the foliage. Fungi Recorded on the Cordyline The plant is apparently very hardy. The follow- ing fungi have been recorded: Colletotrichum cordy- lines Polla., Macrophoma cordylines (Thum.) Berl. and V<^1., Fhyllachora vervisegiua West., Fhyllos- ticta cordylines Sacc. and Berl. CHAPTER 21 CYCLAMEN (Cyclamen persicutn^^ Cultural Considerations. Greenhouse men prefer to sow the cyclamen seed in September and not in spring. In March, the seedlings are transplanted from a two-inch to a four-inch pot and put in a cold frame until large enough to go to a six-inch pot. During the summer, plenty of ventilation and shad- ing should be provided and the plants frequently syringed. In the fall, they are brought into the greenhouse (fig. 52) and some heat provided. The winter temperature should average ^^ to 60 degrees F. until the period of blossoming is over. As the leaves turn yellow, the pots are placed in a cool house, water withheld and the period of rest in- duced. However, a little water is given from time to time to prevent the bulbs from shriveling. Diseases of the Cyclamen Cyclamen are subject to but few serious diseases. Root Rot Caused by Thielavia hasicola Zopf. The disease was reported by Sorauer* as being *Sorauer, P., Ztschr. Pilanzenkrank. 6: i8, 1895. 248 Cyclamen Diseases 249 serious in Germany. The general symptoms are the same as for the violets. For a description of the causal organism and general methods of control, see P- 355- Leaf Spot Caused by Glomerella rufomaculans, var. cycla- minis Patt. and Ch. Symptoms. The spots are circular, watersoaked, with sharply defined borders. The Organism. The acervuli of the causal organ- ism are brownish, large, conidia straight to slightly curved. Sets are few, short and rigid. It is very probable that this conidial stage is the same as thiat described by Halsted as Colletotrichum cyclamens Hals. The ascus stage was found by Patterson and Charles.* The perithecia are dense, found in defi- nite light colored round spots, brown membrana- ceous, subglobose with distinct opening. The asci are eight spored, the spores are hyaline, one celled, oblong to elliptic. The methods of control would be the same as for Colletotrichum cyclamena. Anthracnose Caused by Colletotrichum cyclamena Hals. Symptoms. Anthracnose produces spots (fig. 52) on the leaves which may be mistaken for the spots caused by Fhoma cyclamena. Infection may occur •Patterson, F. W., and Charles, V. K., U. 8. Dept. of Agr. Bur. PI. Ind. Bui. 171 : la-i j, 1910. 250 Diseases of Greenhouse Crops at any part of the leaf and spread in all directions. Cyclamen leaves are especially receptive to infec- tion because of the fact that water is able to lodge and remain a long time. Leaf Spot Caused by Phoma cyclamena Hals. Symptoms. The disease attacks leaves of all ages. The affected portions become darkened. Later the spots become dry and lighter in color, made up of a series of concentric rings of light and dark bands. The dead spots become brittle and drop out at the least touch, giving the appearance of a shot hole. This trouble is different from the leaf spot caused by the Septoria cyclaminis Dur. and M. The causal organisms of both of these leaf spots are little known. Control, Removing the affected leaves and spray- ing with a standard fungicide will materially assist in keeping the disease in check. Dracenas (JDracena fragans) Cultural Considerations. The cultural require- ments of Dracena are the same as for Cordyline, see p. 247. Diseases of Dracenas Dracenas are usually considered a hardy plant. However, they are subject to a few but serious diseases. A * ^^Ht*>tt&LJ(l ■ 1 l^;p' S^\: 1 Hibm Fig. S3- Dracena Diseases. a. Dracena tip blight, b. Pbyllosticta leaf spot (both after Halsted). Dracenas Diseases 251 Leaf Spot and Tip Blight Caused by FJiysalospora dracena Sheld. The conidial stage as first mentioned by Halsted is a species of Gloeosporium. However, the ascus stage was found by Sheldon,* who named it Physa- lospora dracentz. The disease is generally confined to the tip of the foliage (fig. 53, a.). The affected tissue becomes straw colored and shrunken. The disease may be controlled by spraying with a stand- ard fungicide. Phyllosticta Leaf Spot Caused by Phyllosticta macuUcola Hals. Dracenffi, particularly the beautiful species Cordyline terminales, are often subject to a leaf spot which renders them worthless. The disease attacks plants of all ages and sizes. Symptoms. The trouble is characterized by small, brown, somewhat angular spots on the leaves (fig. 53, b.). The tissue adjoining the spots becomes yellowish in color. Within these spots may be found minute black bodies (pycnidia) from which the spores, when ripe, ooze out as long colorless tendrils. Little is known of the organism. The disease may be controlled by spraying. 'Sheldon, J. L., Jour. Myc. 13: i38-i4(^ 1907. 252 Diseases of Greenhouse Crops Leaf Spot Caused by Fhyllosticta dracana Griff, and Maubl. Symptoms. This trouble is manifested as minute, irregular pale spots and bordered by a narrow, brown colored elevated band. The pycnidia are not always present on the spots until the leaves fall off. The spores ooze out as whitish tendrils. This form of spot was first described by Griffon and Maublanc * on greenhouse dracena in France. Its extent in the United States is as yet little known. Leaf Blotch Caused by Vermicularia concentrica Sev. The thicker-leaved sorts such as Dracena goldiena and the variegated D. Lindemi are often subject to a blotch disease. The trouble is characterized by large, brown blotches on the leaves. Very little is known of the causal organism. Spraying with Bordeaux or any other colorless fungicide may con- trol the disease. Daffodils Cultural Considerations, see Tulips, p. 348. Diseases of the Daffodil The Daffodil is a very hardy plant. It thrives equally as well in the greenhouse as it does out of doors. * Griffon, M. M., and Maublanc, Bui. Soc. Mycol. de France 25 : 839, «9io. Daffodil Diseases 253 Yellow Stripe Cause, improper cultural conditions. Symptoms. Yellow stripe is a disease which is more commonly met with tmder field conditions, but also appears on daffodils under glass. The trouble in its early stage is perceptible as a slight discoloration, or a yellowing of the veins of the leaves. In an advanced stage, the leaves become streaked with parallel bands of yellow. In ex- treme cases, the leaves wither and the plants fail to set blossoms. The disease was studied by Dar- lington,* who decided that the cause of it is not a parasitic organism, but that it is due to some uni favorable cultural conditions that are as yet unde- termined. No methods of control are known. Erica (Erica spp.) Cultural Considerations. Ericas are low growing evergreen shrubs which lend themselves admirably to forcing on a commercial scale. Too much or too little water is injurious to the plant especially during the blooming period. The plants should never be allowed to wilt. The pots should be reno- vated every year individually and the proper amount of water given. The plants also need all the ven- tilation possible. * Darlington, H. R., Jour. Roy. Hort. Soc. (London) 34: 161-166, 1908. 254 Diseases of Greenhouse Crops Fungi on the Ericas Ericas are apparently very hardy plants. The only fimgus known to cause a disease on greenhouse plants is Stemphylium encoctonum Br. and De By. The other recorded fungi are as follows : Cystospora ericeti Sacc, Sporonema ohturatum (Fr.) Sacc, Trichosporiutn fuUginosum Karst. Ferns Cultural Considerations. Ferns are propagated by spores, or by division of the clumps. The spores are sown on garden loam over which half an inch of fine sphagnum has bren placed. The spores are scattered evenly, and after being sprinkled with water are covered with a glass. In the division of the crowns, they should be planted and kept in a cool house or frame until they make a good start. Most greenhouse ferns thrive best in a temperature of 60 to 65 degrees F. The following ferns are usually grown on a com- mercial scale: Adianthum cuneatum and A. gracilli- num. Adianthum farleyense seems among the best for decorative purposes. Pteris serrulata is also ex- tensively grown. In large conservatories the tree ferns, especially Alsophila australis, is very much in favor. Of the ferns propagated and sold for dwelling house purposes may be mentioned the sword fern, Nephrolepis exaltata. The latter can stand the atmosphere of a dry room better than any other fern. t Fern Diseases 255 Diseases of the Fern Ferns as a rule are hardy plants when they are given reasonable care. They are, however, attacked by a few diseases which are of economic importance. Tip Burn Cause, physiological. Ornamental ferns grown in greenhouse or in bay windows are often troubled by a tip bum of the foliage. This is generally confined to the tender new growth. Affected leaflets become brown at the tip, giving the entire leaf an unsightly appear- ance. There may be various causes responsible for this trouble. An insufficient water supply at the roots will cause the tender leaflets to wilt. If the soil is allowed to remain dry for any length of time, the wilted parts will dry out and become brown. Poisonous gases either from smoke or fumigation will also cause the tender leaflets to dry up and die, thus giving them a burned appearance. Ex- tremes of heat or cold will have a similar effect on the tender tips of the foliage. Control. It is evident that in this case removing the cause of the trouble will effect a cure. Leaf Scorch Cause, physiological. Symptoms. The trouble appears as prominent 256 Diseases of Greenhouse Crops wedge shaped, reddish-brown spots extending hr- wards from the cleft of the pinnse. Aflfected plants take on a variegated appearance and are less luxuri- ant, but otherwise seem healthy. According to Clin- ton* the scorching may not necessarily be the effect of burning by the sun's rays. It seems, nevertheless, due to the loss of moisture from drought caused by poor watering or to sudden changes of humidity in the air. The fern Adiantum farleyense is very deli- cate, and its thin leaves are more sensitive to un- favorable conditions. Yellows Caused by overwatering or too much nitrogen in the soil. Symptoms. Diseased plants lose their green color and turn white. Growth ceases and all leaflets even- tually drop off (fig. 54). Control. In repotting the plant into new soil it outgrows the disease. Damping Off Caused by Pythium intermedium De By. This disease attacks young fern prothallia. The latter turn soft, limp, and darker in color than the healthy ones. In general structure the organism resembles Pythium de Baryanum. It differs, how- • Clinton, G. P., Connecticut Agr. Expt Sta., 31st and 32nd Ann. Kept.: •549-350> iJoS- Fig. 55- Fern Diseases. a. Host cell invaded with resting ^ores of Completoria cotnplens, &. host cell with fungus body of C. complens, central cell forming resting spores, and some of the peripheral ones developing conidia, d. fungus body in host, the peripheral cells of which develop tubes which penetrate adjacent cells of fern prothallium, d. two young plants in one cell of the host, having en- tered from an adjacent cell {a-d after Atkinson). Fern Diseases 257 ever, with regard to the zoospores. As worked out by Atkinson* the zoospores in P. intermedins arc broadly fusoid, with pointed ends, and terminating at each end in a long cilium. After moving about for five to ten minutes, it gradually comes to a rest, the body undergoing plastic movement until the organism is cut into two parts, forming now two zoospores oval in form and each with a cilium at- tached directly at the smaller end. This peculiarity makes this organism diflferent from Pythium de Baryanum. For control method soil sterilization is recommended (see pp. 32-43). COMPLETORIA DAMPING OfF Caused by Cotnpletoria complens Lohde. Symptoms. The disease attacks yoimg fern pro- thallia. It is manifested as a yellowish or yellowish- brown color of the prothallia as they lay on the soil in the bed or pot. A careful examination will show that the prothallia are spotted, the spots varying from yellowish-green to yellowish-brown, changing to deep brown and to black. In an advanced stage, a prothallium will present a checkered or mosaic appearance. As rot sets in, the prothallium becomes ragged and torn. The Organism. The causal organism was studied by Atkinson.t The mycelium of the fungus is made •Atkinson, G. F., New York (Cornell) Agr. Expt Su. Bui. 94: 247-250, 1895. t Ibid., 252-260^ 1895. 258 Diseases of Greenhouse Crops up of compact clusters of oval or curved branches originating from a common center. This vegetative body occupies asingle cell of the affected prothallium, later putting out a slender germ tube which pierces the adjoining intervening wall, forming clusters of oval mycelial branches which become rounded and play the part of resting spores. Each of them may germinate by sending out a short germ tube at the tip of which a conidium is formed. "When mature, the latter breaks off and is capable of germinating. Upon coming in contact with the host the conidia germinate by sending out a flask-shaped tube which comes close to the wall of a cell. The protoplasm of the conidium now migrates into the inflated germ tube. The latter produces a slender tube which bores its way into the cell of the prothallium, where it swells and grows in a fashion previously described (fig. ^$, a to d.). Completoria complens attacks prothallia of the following ferns: Aspidium (Cyro- tominum) falcatum, Pterisargyria, and Pt. cretica. Very little is as yet known of its method of control. Phyllosticta Leaf Spot, Caused by Phyllosticta pteridis Hals. Symptoms. Ornamental ferns, such as Pteris cretica var. Magnifica are especially susceptible. The first symptoms of the spot disease is loss of the nor- mal green in the frond. This is soon followed by the appearance of the ashy-gray spots surrounded by a border that is either purple or brown. Within the Fern Diseases 259 spot are found minute black pimples, which are really the pycnidia or fruiting sacs of the fungus. The Organism. Fhyllosticta pteridis was first de- scribed by Halsted* in 1893. Since that time the fungus has received no further attention from plant pathologists, hence little is known of its life history. It is probable that spraying with Bordeaux mixture will protect the healthy foliage. Algje Parasites on Ferns Caused by species of Oscillatoria. In damp houses and overwatered soils, the pro- thalia of ferns are often overrun by certain algse which chokes them. This is accomplished by shut- ting out the air and light, interfering with their development and causing them to be completely sterile. As a result, many of the prothalia die. As a control measure, soil sterilization is recom- mended, see pp. 32-43. Gardenia {Gardenia jasminoidesyj Cultural Considerations. Gardenias are very sen- sitive and easily injured if the temperature falls too low during cold nights. By the end of August, it is advisable to maintain some heat at night so that the temperature may be maintained at about 65 degrees F. The plants require an abundance of ventilation. However, the ventilators should be •Halsted, B. D, New Jersey Agr. Expt. Sta., Fourteenth Ann. Rept.: 420-421, 1893. 26o Diseases of Greenhouse Crops opened gradually in the morning and closed like- wise towards the evening. During cloudy days of November and December, care should be taken not to overfeed the plants with liquid manure. Fungi on Gardenias Gardenias are apparently very hardy plants. The following are the recorded fungi: Fumago vagans Pers., Hemileia vastatrix B. and Br., Hypocrella gardenia Henn., and SpKarella gardenia Cke. GENisTiE {Cystisus racemosus canariensis) Cultural Considerations. In the fall, the plants are started at a low temperature of about ^^ de- grees F. The plants are easy to grow and require no special care if proper attention is given to the ventilation and watering. Diseases of Genista Genistje are very hardy plants. There is but one disease recorded by Kirchner* on greenhouse plants. The causal fungus is Ceratophorum setosum Kirch., which causes a disease on leaves and young shoots of Cytisus. Geranium {Geranium sp.) Cultural Considerations. Geraniums are mostly grown as a pot plant to be sold for house or out- * Kirchner, O., Zeit. Pflanzenkrank., 2:324, 1892. Fig 56. Geranium Diseases. a. Dropsy, b. broom rape (a and b after Halsted), c. bacterial rot (after Galloway), d-e. bacterial spot, f. colonies of Pseudomonas erodii (d to f after Lewis). Geranium Diseases 261 of-doors purposes. Geraniums are easily grown. All they need is a soil fairly rich and an abundance of ventilation. It needs plenty of water, but will rot when overwatered. This is especially true for the cutting bed. Diseases of the Geranium The geranium, although a hardy plant, is sub- ject to the attacks of several important diseases. Dropst Cause, physiolc^cal. Symptoms. Dropsy is a serious trouble which is OMifined to the leaves (fig. 56, a) and petioles and blades. Upon the stems and petioles, it appears as peculiar corky ridges. On the blades, it appears as numerous watersoaked specks of a clear amber color when held up to the light. The disease may attack all the plants in the greenhouse. In this case, the older foliage shows best the watersoaked specks. Such leaves soon lose their normal green color, at first turning yellow in spots, then throughout. In extreme cases, although the affected plant forms the normal number of leaves, they remain dwarfed and puny, and are badly specked before unfolding. Plants spotted li^tly often recover when removed out of doors. The disease is worst in the early spring, when it attacks, mostly, young potted gera- niums. As a rule, the blotches and pimples are quite 262 Diseases of Greenhouse Crops evenly distributed. The specks, however, differ in form. Some are very irregular in outline while others are almost circular. Cause. Dropsy is favored by poor light, wet soil, and a high soil temperature. Dropsy may be looked for in late winter with long nights, short days and cloudy weather. This causes an excessive root ac- tion with results injurious to the plant. Control. Dropsy may be controlled by providing a cooler, dryer soil, and by exposing the plants to the direction where they will receive the greatest amount of light and ventilation. Leaf Spot Caused by Pseudomonas erodii Lewis. Symptoms. This disease was found by Lewis * on greenhouse geraniums in Texas. It is not known how serious or how extensive the disease may ap- pear to be in different parts of the country. It is to be assumed that it is more or less prevalent in every greenhouse where it has been spread about by infect- ed plants or cuttings. The disease attacks four varieties of ornamental geraniums and the symptoms are the same on all. On the leaves, the spots first appear as minute dots which are transparent through light. With age the spots enlarge, become reddish brown in the center with a colorless border, resembling much the frog eye spot of the apple (fig. 56, d and e.). There •Lewisj I. M., Phytopath, 4:221-231, 1914. Geranium Diseases 263 is also a tendency to form large spots between the principal veins. In this case, however, infection be- gins at the margin of the leaf and progresses in- wards. Spotted leaves may also become pale and drop oft prematurely. The Organism. Fseudomonas erodii is a short but rather plump rod with rounded ends, borne singly or in short chains of 2 to 3, active by means of polar flagella. It produces no spores, and lique- fies gelatin. Control. There seems no evidence that insects are in any way associated with the spread of the disease in the greenhouse. The causal organism lives in the soil and is spread about by the splashing of water during watering. By the removal of the diseased parts and by careful attention to the water- ing, the disease may be kept in check. The same disease also attacks the wild geranium, Erodium Texanum, which in this case may act as a carrier of the causal organism. This weed therefore should not be tolerated around greenhouses where gerani- ums are grown, nor should it be used in the compost soil. Soft Rot Caused by Bacillus caulivorus Pr. and Del. Symptoms. This disease was found by Gallo- way * to be destructive to greenhouse geraniums. It attacks the stems which at first become soft and mushy and later turn black and shrivel (fig. 56, c). 'Galloway, B. T., Jour. Mycol. 6: 114-115, 1890. 264 Diseases of Greenhouse Crops Cuttings are especially susceptible and rotting usu- ally starts at the cut and works upward, destroying it entirely. Rooted cuttings are not as likely to be- come infected as those freshly made and planted. The disease is most prevalent where yoimg imma- ture cuttings are made, and where the soil has been excessively damp and the house poorly ventilated. Little is known of the causal organism. Damping Off Caused by Pythium de Baryanum Hesse. This disease confines its attacks mainly to gera- nium cuttings. For a description of the causal or- ganism and of methods of control, see p. 17. Gray Mold Caused by Sclerotinia fuckeliana (De By.) Fckl. Symptoms. Gray mold is manifested as dead brown spots on the leaves. Under moisture condi- tions, the gray moldy growth appears. This is but the Botrytis or summer fruiting stage of the fungus. The trouble is prevalent in leaky houses or where water is used in excess and the beds are poorly drained. By proper ventilation, and by careful watering the mold may be kept in check. Leaf Spot Caused by Coniothyrium trahuti Riza. As far as is known this disease is not known to Geranium Diseases 265 occur in the United States. It was first recorded by Ali Riza * as attacking geranium leaves, causing them to dry and shrivel. Broom Rape Caused by Orobanche minor J. Esm. This parasite is frequently met with on clover in the fields. Its attack on greenhouse geraniums was first reported by Halsted.f The seeds of this para- site germinate in the soil. Soon after its roots be- come attached to those of the geraniums. The growth of the broom rape is soon apparent as a pur- plish, erect stem with scale-like purplish leaves above the ground. Later a number of blossoms are formed along the unbranched stem. The attacked geranium becomes sickly in appearance (fig. 56, b.). Steam sterilization of the soil will kill the seed of broom rape. * All Riza, Bui. Trimest Soc. Mycol. France, 28: 148-150, 1912. tHalsted, B. D., et al.. New Jersey Agr. Ezpt. Sta, Twenty- sixth Ann. Kept: 509, 1905. CHAPTER 22 HYACINTH {Hyacinthus orientalis) Cultural Considerations. In forcing (fig. 57, a) hyacinths it is important that they start with a well developed roof system. Otherwise the culture is the same as for narcissus (see p. 287). Diseases of the Hyacinth The few diseases which hyacinths are subject to are serious. Most of these, no doubt, have been brought in with imported bulbs. GuMOSIS Cause, physiological. Symptoms. This trouble is characterized by the formation of pure white gum pockets between the epidermis and lower tissue. In this case the starch apparently becomes replaced by gum through a proc- ess of degeneration. The gum bearing cells often enlarge abnormally. The true cause of this trouble is unknown, but it is generally attributed to im- proper culture. 266 Fig. 57. Hyacinth Diseases. 1, n,"' r ^^""^ of bulb house, b-h. hyacinth yellows, showing type of injury to bulbs, leaves, and blossoms, ». Pseudomonas hyacinthi (b-i after Smith, E. f'). Hyacinth Diseases 267 Soft White Rot Caused by Bacillus hyacinthi septicus Heinz. This disease has been studied by Heinz.* Its presence in this country is unknown. Affected bulbs become soft rotted but remain white. Yellows Caused by Pseudomonas hyacinthi (Wak.) Sm. Symptoms. This disease as described by Smith f and others is characterized as follows : Early infec- tion becomes apparent as water soaked stripes, soon followed by a yellowing then browning and dying of the affected tissue. The water soaked stripes soon spread all over the foliage, and the accompanying symptoms are the same as previously mentioned. The stripes usually start at the apex of the leaves. Frequently, the stripe runs down the entire length of the foliage while both margins remain green. On the flower stalks the disease is also manifested as a water soaked spot followed by the characteristic browning and shriveling. Infection on the bulb is at first confined to the vascular bundles the latter of which become yellow and gorged with slime. The disease soon spreads, invading and destroying the scales, the latter becoming yellow and soggy. Nu- merous other invading organisms often enter and * Heinz, Cent. f. Bakt. 5: 535, 1889. t Smith, £, F., Bacteria in Relation to Plant Diseases, 2:335-3531 1911. 268 Diseases of Greenhouse Crops help to complete the decay and the disorganization of the bulb. Often bulbs are attacked on one side only, in which case the growth of the foliage is also one sided, curved, and bends over towards the dis- eased side (fig. 57, b to h.). The Organism. Pseudomonas hyacintki is a me- dium sized rod, rounded at both ends, and is actively motile by means of one long polar fiagellum (fig. 57, i.). It is non-sporiferous, produces no gas, and liquefies gelatin slowly. Control. It is fortunate that the disease has not as yet proved serious in the United States. It is a very important disease in the Netherlands, and its introduction with imported bulbs should be guarded against by growers in the United States. It is very fortunate that there exists a considerable diflFerence of resistance to yellows among hyacinth varieties, as seen by the following list: SESISTANT Single Red NON-EBSISTANT Robert Steiger Gertrade Homenis Siniie Rose Baroness v. Tuyll Charles Dickens Moreno Sinele WhiU Grandeur a Merveille LaGrandesse La Franchise LaNeige Single Light Blue Grand Maltre Captain Boyton La Pe3nouse Czar Peter Regulus Leonidas Lord Derby Lord Pahnerston Orandates Queen of Blues Scbotel Hyacinth Diseases 269 XBSISTANT NON-RESISTANT Singfe Dark Blue King of the Blues Aigus General Havelock King of the Blacks Masterpiece Mimosa Single Yellow and Orange Kini? of the YeUows Bird of Paradise Yellow Hammer Hermann Ida La dtromere L'or d'Australie Dovble Red Princesse Royale Double Rose Bouquet Royal Double White Flevo Florence Nightingale La Virginity Grand Vain Queen La Tour d'Auvergne Double Dark Blue Crown Prince of Sweden In Holland the disease is kept in check by the de- straction of diseased plants. Diseased bulbs should never be planted since they will surely introduce the disease in new localities. Spraying in this case will be of no benefit. Damping Off Caused by Dictyuchus monosporus Seitg. Symptoms. The above fungus causes a serious damping off, the symptoms of which resemble those of other plants. Dictyuchus monosporus is the only one of the genus Saprolginiacese which is reported by Halsted as being parasitic on plants. The Organism. The sporangia are clavate. The swarm spores become walled within the sporangium 270 Diseases of Greenhouse Crops and emerge singly through its lateral walls. For methods of control soil sterilization is recommended (see pp. 32-43). Bulb Rot Caused by Rosellinia massinkii Sacc. This fungus is reported by Halsted * as thriving on hyacinth bulbs. However, the nature of the in- jury is not clearly stated by him. The Organism. The fungus produces dark brown, elliptical spores. The asci are borne in globose or depressed dark colored perithecia. SCLEROTINIA ROT Caused by Sclerotinia bulborum Rehn. Symptoms. The disease is first manifested as yel- low stripes or blotches on the leaves and bulbs. With the advance of the trouble, a velvety olive brown mold is formed on the surface of the spots. This growth is but the conidiophores and conidia of the causal fungus. The black sclerotia are developed on the rotted bulbs, and are found mostly within the outer scales. As the sclerotia winter over, they germinate by sending out slender stalks which bear apothecia and ascospores. The Botrytis form of spores is the most prevalent and is depended upon by the fungus to spread it quickly from plant to plant. * Halsted, B. D., N. J. Agr. Expt. Sta., Fourteenth Ann. Kept 393. 1893- Hyacinth Diseases 271 Control. Since numerous sclerotia are left in the soil with decayed bulbs, steam sterilization of the soil is recommended. Badly infected bulbs should be removed and destroyed by fire. Plenty of ven- tilation should be provided whenever possible. Nematode Caused by Tylenchus dipsaci Kuhn. Symptoms. This disease was first found in the United States by Byars * on imported hyacinth bulbs. It is prevalent in Europe where it attacks besides the hyacinth, clover, alfalfa, rye, oats, onion, potatoes, and numerous other wild and cultivated plants. On the leaves, the nematode produces character- istic distortions and yellow to brown longitudinal discolorations. At the end of the growing season, the parasite migrates from the leaves to the scales of the bulbs. Diseased scales become discolored, so that when one cuts through an infected bulb, one or more yellow characteristic rings become very appar- ent. The Organism. The adult worm is barely per- ceptible to the naked eye. It may, however, be read- ily seen with a magnifying hand lens. Each female produces numerous eggs which hatch into larvse, the latter of which reach maturity quickly. This means that several generations are produced in one season. Control. The disease is carried with infected * Byars, L. P., Phytopath. 4:45, 1914. 272 Diseases of Greenhouse Crops bulbs. The latter should therefore be discarded and only healthy ones used. Grape Hyacinth {Muscari hotryoides) Cultural Considerations. As soon as the bulbs are brought in the house, they should be given the bene- fit of the full light, and a low temperature. Neg- lect in this direction will result in spindly weak plants. Fungi of the Grape Hyacinth This plant is apparently very hardy. There are but two fungi recorded on this host : Vromyces scillarum (Grev.) Wint., TJstilago vaillantii Tul. Hydrangea (Hydrangea kortemis) Cultural Considerations. Hydrangeas are valu- able because of their adaptability to forcing for the Easter trade. Plants should be brought in the early part of January and freed from all old and dead leaves. The beginning temperature should be about 45 degrees F. and after two weeks it should be raised ten more degrees. To force them to flower the tem- perature is raised to 65 degrees. Ten days before Easter the blooming plants are given a temperature of 50 to ^^ degrees. This hardens the blossoms and gives them better keeping qualities. During active growth they need plenty of ventilation, sunlight, and water, and frequent syringing. Hydrangea Diseases 273 Diseases of Hydrangeas Hydrangeas are very hardy plants. They are sub- ject to but few diseases, which are of little impor- tance. Rust of Hydrangea Caused by Pucdniastrum hydrangea (B. and C.) Arth. Rust is a serious disease on hydrangeas. The ure- dinial and tetial stages of the causal organism are do- ing the damage. Selby * was perhaps the first to have observed the rust, although little more has been added to our knowledge of it or of methods of con- trol. The Organism. As far as is known Pucdniastrum hydrangea has only two spore stages, the uredo and teliospores. The uredinia are found scattered most- ly on the under side of the leaf, their color dark yellow to pale yellow. The peridium is delicate, the cells are small, while the walls are thin throughout. The ostiolar cells are somewhat elongated, and slightly pointed, the spores are broadly elliptical to ovate; the cell wall is thin and warty. The telia are usually found on the lower part of the leaf in small angular groups, that are rather flat and reddish brown in color. Spores are formed in a single layer within the epidermal cells or immediately beneath it; the cell wall is thin, and a dark, cinnamon brown in color. No methods of control are known. The 'Selby, A. D., Ohio Agr. Expt Sta., Bui. 214: 402, 19x0. 274 Diseases of Greenhouse Crops disease may be introduced into the greenhouse with infected plants. Leaf Spot Caused by Fhyllosticta hydrangea E. and E. The disease is characterized by large, rusty, brown spots occurring on the leaves, especially at the edges. The disease is often so severe that it is necessary to cut off the top of the plant. Upon examination of the affected leaves, numerous minute, black pycnidia will be found scattered throughout. The conidia are oblong, hyaline, and one celled, and generally ooze out as minute creamy tendrils. The disease may be kept in check by spraying with a standard fungicide. CHAPTER 23 LILAC {Syringia vulgaris) Cultural Considerations. Indoor lilacs at first re- quire a cool ho\ise. The temperature is gradually in- creased to about 60 degrees. The plants require fre- quent sjrringing and moderate ventilation. Diseases of the Lilac Forced lilacs are subject to a few diseases. The plant is generally considered very hardy. Leaf Blight Caused by Pseudomonas syringe van. Hall. Symptoms. The disease as described by Gussow * seems to be confined to the leaves. The writer has found a blossom blight of the lilac both indoors and in the field. In pure culture, the organism resem- bled P. syringa. The affected leaves become greatly disfigured; the disease spreads very rapidly. Control. It is doubtful whether spraying will be of any avail. The plants should be given plenty of ventilation whenever possible. Diseased leaves should be destroyed by fire. As far as possible the * Gussow, H. T., Gard. Chron. 44: 404.-405, 1908. 275 S76 Diseases of Greenhouse Crops leaves of the plants should be kept dry; all the water should be applied with the hose on the ground, a method that also avoids the splashing of soil par- ticles. Twig Blight Caused by Fhytophthora syringa Kleb. This disease was found by Klebahn * to be very serious in propagating beds in Germany. The causal organism attacks and kills the twigs at a distance of several intemodes above ground. The flower buds from the affected shoots fail to develop alto- gether. However, new shoots may appear below the affected area. The disease is of no economic sig- nificance in the United States. Powdery Mildew Cimstdhy Microsphara alni (Wal.) Salm. Symptoms. Powdery mildew is perhaps one of the commonest troubles of forced lilacs. The dis- ease is characterized by white powdery patches on the surface of the leaves and stems of the plant. The causal fungus attacks a large number of outdoor plants besides the lilac, as chief of which Lonicera, Alnus, Betula, Quercus, Carya, Castanea, Juglans, and Platanus may be mentioned. Outdoor lilac often suffers greatly from this mildew. The Organism. The perithecia are either scat- * Klebahn, H., Krankheiten des Fielders (Berlin) : 75, 1909. Fig. 58. Lily Diseases. a. Type of lily house, b. healthy bulb, c Bermuda disease (after Woods), d. Botrytis disease (after Halsted). Lilac Diseases 277 tered or crowded greatly, varying in size. This seems also tfue for the appendages, which vary in length and in numbers, but are rigid, and colorless throughout, excepting the amber brown base, and dichotomously branched at the tips, the latter branches being regularly recurved. The asci are short stalked, ovate to globose; the ascospores are 8 in number. Control. This mildew may be controlled in the same way as the rose mildew (see p. 323). Lilies (Lilium longiflorum) Cultural Considerations. The secret of success with lilies is in strong and vigorous bulbs. Lilies forced for the Christmas market should be planted in a rich soil thoroughly mixed with well rotted stable manure. After having been potted, the bulbs should be placed in a cold frame or in a cool dark cellar to encourage the rapid rooting. After that they are maintained at a temperature of 50, then 60, then 75 degrees F. in the house. Lilies for the Easter trade are bought about the middle of Decem- ber. Lilium speciosum var. rubrum is especially well adapted for forcing. Diseases of Lilies Lilies are subject to quite a number of diseases all of which are of economic importance. 278 Diseases of Greenhouse Crops The Bermuda Disease Cause, cultural and mites. Symptoms. The trouble is characterized by a spotting and distortion of the leaves, flowers, and scales of the bulbs, as well as by a general stunting in growth. In severe cases, there appear yellowish white, longitudinal, sunken spots, and streaks on the first leaves as they show above ground. As growth proceeds each succeeding whorl becomes similarly aflFected, and finally collapses and dries. Even the flowers become spotted, shrunken, and distorted. Occasionally plants appear healthy, until the disease suddenly breaks out on the flowers. It is seldom that all the leaves in the same whorl are uniformly affected (fig. 58, b and c). The diseased foliage or whorls may be irregularly scattered along the main stalk. The greatest damage occurs when the flowers are spotted, since the plants become un- salable whether the leaves are healthy or not. Cause. There are many current theories as to the cause of the disease. Some growers believe that it is due to soil exhaustion. Others believe that it is due to the removal of the flower stalks by the growers in Bermuda, who desire to sell them, thus giving them a double source of profit. It is claimed that this practice weakens the bulbs by depriving them of their proper nourishment. Still others are of the opinion that the bulbs become weakened by being harvested prematurely. Finally some growers hold that the trouble is due to an insect which feeds on Lily Diseases 279 the scales of the bulbs. The investigations by Woods* have shown that the trouble is brought about by a combination of causes. Poor cultural conditions such as overwatering, or the use of poor, unselected bulbs will generally and indirectly tend to cause this disease. The bulbs may be further weak- ened by the attacks of a mite {Rhizoglypkus echi- nops) and of certain fungi and bacteria. The bulbs may also become weakened by allowing the roots to dry and then overwater. Control. The disease cannot be cured. The best that can be done is to select strong, healthy bulbs. Crop rotation to prevent the spread of the mite is also recommended. Rust Lilies are subject to several rust diseases. The most important is the American rust and is caused by a species of Vromyces. This disease according to Halsted t was first found on leaves of Lilium can- didum at Buffalo, N. Y. The Botrytise Disease Caused by Botrytis sp. Symptoms. The trouble is apparent as small rusty spots upon the buds, leaves, and blossoms. •Woods, A. F., U. S. Dept. of Agr. Div. of Veg. Phys. and Path. Bui., 14: 7-15, 1897. t Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Annual Kept: 392, 1893. 28o Diseases of Greenhouse Crops With the advance of the disease, the spots become coated with a fuzzy, brownish coat, made up of the fruiting stalks. As the plant becomes decayed, numerous sclerotia appear. The disease is spread in the hothouse through the watering or in syringing. Infection is favored by a high humidity and poor light conditions in the house. Little is known of the causal organism (fig. 58, d.). Control. The disease may be kept in check by proper ventilation. Calla Lily (^Aracea spp.") Cultural Considerations. The yellow callas are grown in the same way as the white callas except that they seem to do better without a rest period. White callas require a rich soil, full simlight and an abundance of water during the growing season. During the summer, the plants undergo a resting period. The pots are laid out in the open in the shade and a little water is given occasionally to pre- vent the Rhizomes from drying out. Diseases of the Calla Lily Callas are apparently a hardy plant. It is sub- ject to but few diseases. Soft Rot Caused by Bacillus aroidea Town. Symptoms. This disease may be foimd both on Lily Diseases 281 calla lilies in the greenhouse or in the field. The callas usually rot off at or below the surface of the ground, the disease frequently spreading downward in the direction of the corms and upward into the leaves. Occasionally soft rot starts at the edges of the leaves or at the flower stalk. The disease spreads more rapidly and is also worse in green- houses where callas are grown in solid beds. In cutting open a diseased corm, one observes a line of demarkation between the healthy and dis- eased tissue, the latter being brown, soft, and water soaked. Affected leaves become slimy without nec- essarily losing their green color. If the disease at- tacks flower stalks, the flowers turn brown and the stalk falls over although its green color is preserved. As the disease progresses under ground the plant above ground topples over without any sign of dis- ease. Under unfavorable conditions, the disease in the corm may not progress further than a small spot which soon dries. The causal organism, however, remains alive in these spots, but dormant until the time when conditions of moisture and temperature again become favorable. The nature of the soil de- termines to a large extent the severity of the rot. A soil rich in humus is most favorable for its spread. The Organism. Bacillus aroidea is a short rod with rounded ends, single or in chains of two or four. Its growth is white on solid media. It produces no gas, and liquefies gelatin. Although apparently dis- tinct from Bacillus caratovorus Jones, it is neverthe- less capable of producing a soft dark colored rot in 282 Diseases of Greenhouse Crops carrot, potato, turnip, radish, cabbage, cauliflower, tomato, and in the fruit of eggplant and cucumber. Control. The disease may be prevented from get- ting a start by discarding diseased or spotted conns. Changing the soil every third or fourth year, or steam sterilizing it will prevent infection of the healthy corms. Starting the plants in pots instead of planting them directly in the beds is also recom- mended. In this way, all diseased plants will be discarded before being put finally in the bed. Blight Caused by Phyllosticta richardie Hals. Symptoms. This disease is characterized by large, ashy spots on the leaves. Within these spots may be found minute, dark fruiting bodies (pycnidia). Very little is known of the causal organism. Blight may often be confused with a spotting due to sun- scald. In this case, however, the dead tissue is in- vaded with the fungus Pestalozzia richardia Hals. Leaf Blight Caused by Cercospora richardiacola Atk. Symptoms. This disease was first foimd by Pro- fessor Atkinson in Alabama in 1891. The spots are black with small white centers, and may be formed on all parts of the leaves. The Organism. The conidia are hyaline, and from 4 to 10 septate. The conidiophores are borne in Lily Diseases 283 bundles and are brownish to reddish in color, finally becoming reddish brown with age. Control. This disease may be kept in check by spraying with a standard fungicide. Japan Lily Disease Caused by Rhizopus means Mass. Symptoms. This disease is characterized by a soft; rot of lily bulbs, especially Lilium speciosum, and L. auratum. The malady was studied by Massee * who found it on imported bulbs from Japan. The causal organism seems to be a wound parasite, that gains entrance to the roots through a wound. From the roots, it works its way up to the scales and causes them to rot. Diseased bulbs generally become cov- ered by a white weft of mycelial growth which is soon followed by numerous clusters of sporophores bearing black globose sporangia. The Organism. The mycelium is white, the sporo- phores forked or simple. Sporangia globose, black- ish to deep brown, columella large. Spores striated, pale olive. Zygospores dark, and covered with spiny warts. Control. Where the disease occurs once, the soil should not be used again unless it has been sterilized with steam or formaldehyde. Injured bulbs should not be planted. In shipping bulbs, care should be taken that they are not packed damp. * Massee, G., Diseases of Cultirated Plants and Trees: 133, 1910 (Macmillan Co., New York). 284 Diseases of Greenhouse Crops Blight of the Variegated Plantain Lily {Funkia Undulata. var. Variegata) Caused by Colletotrichum omnivorum Hals. Symptoms. This blight is severe on the broad and the narrow leaved varieties, and especially on Funkia undulata var. variegata. The disease ap- pears as spots at about the middle of the leaf. The tissue in these soon drop out, leaving the veins which run lengthwise. Badly diseased foliage have a shredded appearance. The same disease also at- tacks Aspidistra lurida var variegata, a plant closely related to the Funkia. At present, little is known of the nature of the causal organism. Control. , Halsted * recommends spraying with Ammoniacal copper carbonate. Attention should be paid to securing resistant varieties. Lily of the Valley (Convalaria majalis') Cultural Considerations. This plant may be forced at any time of the year. Sand is the best soil in which to grow it. It is advisable to begin with a bottom heat of 50 degrees F. and quickly raise it to 85 degrees. The plants require an abimdance of water during the forcing period. Diseases of the Lily of the Valley Lily of the Valley is considered a hardy plant. They are however known to suffer from two diseases. 'Halsted, B. D., New Jersey Agr. Expt Sta., Thirteenth Ann. Kept: 296, 1893. Lily Diseases 285 Rot Caused by Botrytis paonia Oud. This disease, which is usually common on peonies and on lilacs, also frequently attacks the lily of the valley. The causal organism often attacks the pips first; then works its way up to the stems. Infected pips become soft, then become covered with a gray- ish mold, and are later peppered with greenish-black, flat sclerotia. Control. The disease is often introduced with in- fected pips which have been previously injured, or kept under poor storage conditions, especially under too high temperatures and moistures. Hence only healthy pips should be used. If the soil becomes in- fected with the causal organism, it should be steam sterilized, or treated with formaldehyde (see pp. 32- 43) the former method being preferred. Leaf Spot Caused by Dendrophoma convallarie Can. This leaf spot often destroys entire beds of plants. Little is known of the causal organism or of methods of control. Septoria Leaf Spot Caused by Septoria majalis Aderh. This disease is characterized by a general spot- ting which is unevenly scattered over the leaves. The spots, however, are found mostly on old and faded 286 Diseases of Greenhouse Crops leaves, hence the trouble is of no economic impor- tance. Mignonette {Reseda odorata) Cultural Considerations. The soil required for mignonette is about the same as for carnations. Raised benches are preferred rather than pots. An inch of well rotted stable manure is placed at the bottom, and four inches of the compost on top. Young seedlings require an abundance of ventilation. During bright weather temporary shading is neces- sary. Mignonette is very sensitive to overwatering. The watering should be done in the morning. If water remains on the foliage over night, the plants will become badly spotted. The temperature of the house in cloudy days should not run above ^^ degrees F. and in bright days not higher than 65 degrees. Diseases of the Mignonette Mignonette is subject to but few diseases. The most important of these may be mentioned as fol- lows: White Rust Caused by Cystopus Candida (Pers.) Roussel. This disease is commonly met with out of doors on practically all cultivated cruciferous plants. In Europe, white rust seems to attack the mignonette, but there are no records of similar cases in the United States. Mignonette Diseases 287 Leaf Spot Caused by Cercospora reseda Fl. Symptoms. The trouble becomes apparent as minute pale spots with yellowish to brownish bor- ders. In spreading over the entire leaf, it takes on a reddish discoloration. Usually, the lower leaves are most affected. Little is now known of the causal organism. Root Rot Caused by Rhizoctonia sp. Root rot of mignonette may be expected wherever the soil in the benches is infected with Rhizoctonia. The young plants usually damp off. Older ones rot at the base of the stem and at the roots. In either case, affected plants are dwarfed, and the leaves have a sickly yellow color. For a description of the or- ganism and for methods of control, see p. 20. Narcissus (^Narcissus bulbocodium) Cultural Considerations. Narcissus is easily forced. After potting, a thorough watering should be given, as the bulbs fail to set roots in a dry soil. The pots should be placed in a cool cellar to en- courage root formation and to retard top growth. After bringing the pots into the greenhouse, they should at first be placed under the benches or under subdued light, and in a low temperature of about 50 degrees F. Later the plants are gradually ex- 288 Diseases of Greenhouse Crops posed to more light. The more slowly they are forced the better the quality of the flowers. Dur- ing the blossoming period great care should be given to the watering. At no time should the root system be permitted to become dry. On bright days the tops of the plants should be syringed until the flow- ers begin to show color. Diseases of the Narcissus Narcissus under normal care is very hardy and subject to very few diseases. Rust Caused by Puccinia schrceteri Pass. This rust often attacks Narcissus poeticus. It is of no economic importance in the United States. Bulb Rot Caused by Fusarium bulbigenum Mass. Symptoms. This trouble, which was studied by Massee,* is said to be prevalent in England. Its presence in the United States has not been reported. The trouble first appears on the leaves as small yellowish spots. These, however, enlarge and work downward into the bulb scales, the latter of which soon rot. The disease is spread by partly diseased * Massee, G., Roy. Bot Gard. Bui. Misc. Inf.: 307-309, 1913. Narcissus Diseases 289 bulbs and through infected soil. Little is now known of the causal organism. Control. Care should be taken to prevent the in- troduction of this disease into this country. All bulbs which show the least discoloration should not be used for planting. CHAPTER 24 ORCHIDS {Orchidacee) Of the numerous orchids, the following are the important commercial genera with their cultural requirements : Culture of Calanthe These are easily grown in pots or in beds, about one-third space being devoted to drainage by means of a layer of clean sphagnum. The pseudobulbs are then planted in a compost which is made up of one-third chopped sod with the fine soil removed, one-third chopped live sphagnum and leaf mold to which charcoal is added as a sweetener. Calanthes require a winter night temperature of about 50 to' 55 degrees and a day temperature of 65 to 70 de- grees F. The plants require an abimdance of water during the growing period, but less when the leaves start to drop and blossoming begins. At this stage, only enough water is needed to keep the blossoms from wilting. When the blossoming season is over the plants are given a six weeks' rest. The pots with the pseudobulbs are laid on the side in a dry warm place and the soil kept dry. 290 Orchid Diseases 291 Culture of Cattleya These plants require perfect drainage conditions. They thrive best in osmunda fiber pots. On a com- mercial scale, it is not desirable to cover the plants with moss as this usually harbors slugs which are fond of the blossoms. Cattleyas require frequent syringing with the hose. The temperature required is the same as that for Calanthe. After flowering the pseudobulbs need a rest. In this case they re- quire enough water to prevent them from drying. Cattleyse thrive best when grown near the glass. Culture of Coelogyne The cultural requirements are the same as for Cattleyae, the pot culture, however, being preferred. The plants are heavy feeders, hence weak manure water may be applied once every week during the growing season. After flowering the plants are re- potted and kept in a cool house until about Sep- tember. Culture of Cypripedia These plants require no rest period, hence may be grown the year round. They require a winter night temperature of 60 to 65 degrees F. and a day temperature of about 70 degrees F. As spring approaches a higher temperature may be given, and the glass lightly shaded. However, in the winter the plants require the full sunlight. 292 Diseases of Greenhouse Crops Culture of Dendrobium These plants seem to thrive best in small pots or baskets. They also require an abundance of water during the growing season, and a night temperature of about 65 degrees F. When flowers appear the plants become destitute of leaves, at which time only enough water is applied to prevent the pseudo- bulbs from drying. Culture of Lslia These plants require a sunny location and an abundance of overhead water during active growth. Culture of Lycaste These plants nped to be kept as cool as possible in the summer; otherwise, the culture is the same as for Cattleya. Culture of Odontoglossum These plants require an abundance of ventilation, and a cool moist temperature during the summer. They are grown in pots or baskets filled with soil made of equal parts peat, live sphagnum moss, and osmunda fiber. Culture of Oncidium These plants require a bright, warm house and are suspended from the rafters in small baskets. Orchid Diseases 293 Culture of PHALiENOpsis These plants require plenty of ventilation, but too much of it should be avoided. Frequent syringing is necessary and the temperature requirements from 70 to 75 degrees F. at night and about 90 to 95 degrees during the daytime. Culture of Vanda These plants require shade after February. They prefer a night temperature of 65 degrees F. and seem to thrive best in baskets near the glass. Spot Disease of Orchids Cause, mechanical injury. Symptoms. This disease is manifested as minute pale spots on the upper side of the leaf. The spots vary considerably in size, arrangement, and num- bers, and may occur on any parts of the foliage irre- spective of age. The trouble may be easily over- looked, due to the light color and the superficial na- ture of the spots. With age, however, the spots may go through the entire tissue of the leaf. The cause of the trouble, as explained by Massee,* is of non-parasitic origin. It is brought about by the presence of minute drops of water on the surface of the leaves during very low temperatures while the roots are too copiously supplied with water. The *Mawee, &, Annals of Bot. 9:422-429, 1895. 294 Diseases of Greenhouse Crops water drops produce a chill which causes the content of the underlying cells to plasmolyze. This is fol- lowed by the precipitation of tannin and the disin- tegration of the cells. The method of control would consist in the careful watering of the plants during cool weather. Orchid Deterioration Cause, cultural. Florists are aware of the fact that imported or- chids often run out and deteriorate after a year or two of culture under glass. Attention has been called to a similar trouble by TruflEant and Hebert.* They maintain that deterioration is due to an in- crease in the percentage of mineral matter and a de- crease in the percentage of nitrogen in the deterio- rated plants. The trouble, it is believed, is due largely to improper nutrition imder cultivation. Leaf Spot of Orchids Cause unknown. This disease is often found on hybrid Calanthes. It is manifested as large and small dead patches on all the parts of the plant. The leaves especially become imsightly, and as a result the blossoms are small and stunted. This disease was first described by Bidgood t on greenhouse hybrid Calanthes. The * Truffant, &, and Herbert, A., Jour. Soc. Nat. Hort France, 19 : 85-98, 1897. t Bidgood, J., Jour. Roy. Hort. Soc. 29: 124-127, 1904. ■"^ ^ b "^ O »' e @ Fig. 59. Orchid Diseases. o. Volutella blight of Bletia (after Halsted), b. rust, Hemileia oncidi (after Griffon and Maublanc), c. Sobralia anthracnose (after Halstrd), d. bacterial leaf spot, partly diseased leaf with cells invaded by the organism (after Hori, S.). Orchid Diseases 295 cause of the disease and methods of control are as yet unknown. Bacterial Leaf Spot of Orchids Caused by Bacillus cypripedii Hori. Symptoms. According to Hori,* this disease is prevalent in Japan and is greatly feared there. The disease attacks the most valuable orchids and ruins them in a very short time. The disease is manifested as light amber-colored spots on the leaf blades. The spots quickly enlarge, and in a few days the entire leaf becomes invaded and discolored. A few days later the diseased foli- age turns brownish and later a deep chestnut brown; the upper surface becomes wrinkled, with loss of luster. The lower surface of the leaves, just imdemeath the spots, rapidly take on a faintly pale color, and only gradually assumes the same color as that of the upper part. If infection takes place on the lower portion of the leaf, the upper half soon becomes yellowish and dies off as a result of lack of food (fig. 59, d.). The rot from the leaves works down to the stem, involving the entire plant. The disease (also known as brown rot, brown spot) attacks orchids with fleshy, succulent leaves, such as Phalsenopsis amabilis. Ph. schileriana Cyp- ripedium haynaldium, C. philippinense, C. Iseviga- tum, C. godefroyse. The more susceptible varieties seem to be Phalxnopsis schilleriana and Cypripedium *Hori, S., Centralb. fur Bakt, 31:85-92, 1911. 296 Diseases of Greenhouse Crops phillipinense. Infection takes place by means of a wound. The Organism. Bacillus cypripedii is a medium sized slender rod-shaped organism, rounded at both ends, occurring in chains of 2-3, and motile by means of ilagella. On agar it forms a smooth, light grayish white colony with a pearly luster, and a dirty cream-colored growth on potato plugs. It pro- duces a film on bouillon, coagulates milk, and rap- idly dissolves gelatin. It is not known whether the causal organism is the same or closely related to the one described by Peglion * under the name of Bac- terium oncidii Peg, as causing a disease on orchids. Very little is known of the methods of control. Since infection takes place through a wound, care should be taken to prevent careless washing with a rough sponge. Diseased material should be de- stroyed by fire. Rust of Orchids Caused by Hemileia oncidii Griff and Maubl. Symptoms. The disease is characterized by mi- nute yellowish spots, the surfaces of which become covered with an orange-colored powder which is made up of the spores of the causal organism. The spots enlarge, the center turns brownish, while the advancing margin remains an orange rust color. The disease was first described by Griffon and Mau- * Peglion, v., Centralbl. fiir Bakt. 5:33, 1899. Orchid Diseases 297 blanc,* who found it on orchids in greenhouses in France. It is not known whether this rust is of any importance in the United States, The only danger consists in its being imported from abroad with im- ported plants. The causal organism produces only teleutospores. It feeds on its host by means of haustoria sent into the interior of the cells (fig. 59, d, 1-9.). Rust of Orchids Caused by Uredo behnickiana Henn. Symptoms. This rust does not produce any strik- ing symptoms. Hence it may readily be overlooked. AflFected leaves are covered with minute, reddish- colored sori. When mature, the epidermal covering of these sori breaks away and liberates a reddish powder which is made up of thousands of the spores of the fungus. This rust is found on living leaves of Oncidium dasystelis and was described by Hen- nings t as a serious disease of orchids imported to Germany from Brazil. It is not known whether this disease is present in this country. Its introduction should therefore be guarded against. Uredo be- hnickiana differs from U. onicidii Henn, in that the latter causes rounded thickened red-brown spots on Oncidium lavecanum. * Griffon, M. M., and Maublanc, Bui. Soc. Mycol. de France 25: 13S-139. 1909- t Hennings, P., Hedwigia 44: 169, 1904. 298 Diseases of Greenhouse Crops Petal Blight Caused by Sclerotinia fuckeliana (De By.) Fckl. Greenhouse growers are often troubled with a petal blotch of orchids. This disfigures the blos- soms, and consequently ruins their market value. The disease appears as small spots over the entire sur- face area of the petals. Frequently the spots are bor- dered by a delicate ring of pink. Perhaps another stage of this disease is marked by the large spots which cause the petals to become disorganized. Af- fected petals either drop off or stick to the now worthless blossom. On examination of the spotted petals, there will be noticed a gray mold growing on the surface of the affected tissue. This is but the fruiting stalks of the causal organism. This gray mold will also be found on faded blossoms, and if allowed to remain in the greenhouse will saturate the place with the spores of the fungus. Control. All affected blossoms should be cut off and destroyed. This simple precaution will remove the host upon which the fungus is able to thrive as a saprophyte. Rot Caused by Nectria bulbicola Henn. This trouble is manifested as a rot on the pseudo bulbs of Macillaria rufescentis. It was originally found by Hennings* on orchids brought in from Venezuela or Trinidad. * Hennings, P., Notizbl. K. Bot. Gasten u. Mus. Berlin. Orchid Diseases 299 There are other Nectria recorded on orchids: Nectria vanda Wahrl on root of Vanda suavis, Nectria goroshankianna Wahrl., Nectria {Dialo- nectria) binotiana Sacc, and Nectria (D.) phyllo- gena Sacc. on leaves of epiphyte orchids in Brazil. Anthracnose of Orchids Caused by Physalospora cattleya Maub. and Las. Symptoms. This trouble is manifested as yellow- ish light spots the tissue of which becomes soft. When the epidermis is torn away from one of the spots a clear liquid will ooze out. At this stage of the malady infected leaves lose their normal color, collapse, and drop off. Ordinarily there is no fruit of any fungus formed on the spots, but under moist conditions the acervuli of the causal fungus appear. The disease, although attacking the foliage, does its greatest damage to the stems. In- fection can take place only through a wound made in the epidermis. The Organism. It is only the summer stage of the fungus, Gloeosporium macropus Sacc, which causes the disease on orchids. The same stage also produces a similar disease on foliage of Haya car- nosa. Citrus aurantium aiid Aloes. Its occurrence on orchids was called attention to by Mangin,* who found it to be a serious disease of greenhouse orchids * Mangin, M. L., Jour. Soc. Nat. d'Hort. de France 19: 449-452, 1897. 300 Diseases of Greenhouse Crops in France. It is doubtful if it is yet to be feared in the United States. Control. Care and vigilance should be exercised to prevent the introduction of the disease to the United States. All infected material should be de- stroyed by fire and the plants should be sprayed with a standard fungicide. American Anthracnose Caused by Glomerella cincta (B. and C.) S. and S. The American anthracnose is very prevalent on hothouse orchids. The variety most susceptible to the disease is Sobralia macramtha. The trouble is first noticed by a discoloration on the stems which soon become brown almost to black while the tender interior tissue becomes soft and decayed. Later the spore pustules appear in great abundance on the dead parts. On the leaves the disease works in a way similar to that found on the stems. The trouble, however, nearly always starts from the tip and works downwards (fig. 59, c). There is usu- ally a distinct line of demarkation between the healthy and the diseased tissue. The Organism. The conidial or summer stage of the fungus was described by Halsted.* The conidia are elliptic and guttulate. Setffi may often be present, but they are generally obscured by the * Halsted, B. D., New Jersey Agr. Ezpt. Sta., Fourteenth Ann. Kept.: 414-41S. i893. Orchid Diseases 301 great masses of spores formed in the acervuli. The ascus or winter stage was discovered by Stoneman.* The perithecia are flask-shaped, the asci are clavate. The ascospores vary from elliptic to curved in shape. Control. Before attempting anything else, the source of infection should be removed. All infected plants should be destroyed by fire. Spraying with Bordeaux mixture 4-4-50 will help to protect the plants from becoming infected. Bletia Anthracnose Caused by Colletotrichum bletia Hals, The beautiful Bletia orchid is often subject to the attacks of an anthracnose, the cause of which is due to a closely associated organism of the Sobralia anthracnose. On the Bletia, the trouble is mani- fested as a spotting that disfigures the leaves and reduces their usefulness. The spots are almost black and very soft. As this disease progresses, the soft tissue rots and breaks away the fibrous portions. Usually the trouble begins at the tender tips, and causes affected foliage to have a ragged appearance. The Organism. In structure the organism resem- bles other Colletotrichums. The acervuli are light brown in color and possess numerous dark setae. Control. The trouble may be kept in check by spraying with Bordeaux mixture. It is also essen- tial to destroy by fire all dead and diseased material * Stoneman, B., Bot. Gaz. 26: 69-120, 1898. 302 Diseases of Greenhouse Crops and to prevent them from finding a place in the manure or compost pile. European Anthracnose Caused by GlcBosporium affine Sacc. This disease has been reported by Sorauer* as very serious on cultivated orchids. The trouble is prevalent in overheated hothouses and on plants which have been excessively fertilized. Symptoms. On the leaves, anthracnose causes a discoloration and a drying which starts at the tip, or at the periphery or border. Usually the young- est foliage is attacked first. In severe cases, the older leaves and even the bulbs become diseased, wither, and dry up. The disease is carried about with infected bulbs. The same trouble also attacks other orchids such as Cattleya Mendelii and Cypri- pedium laevegatum. The Organism. In structure, GloBOsporium affine differs very little from other Gleosporiums. The fungus attacks the epidermis, then works into the mesophyllic layer of cells, where the chloroplasts are destroyed. This explains the disappearance of the green coloring matter in the affected parts. The spore pustules are formed under the epidermis, the latter bursting as the spores accumulate. The spores are formed on what appears to be a pseudostroma. The spores are one-celled, hyaline, cylindrical, and •Sorauer, V. P., Zeitsch. PflaDzenkr. 21:387-395, 1911. Orchid Diseases 303 often slightly curved. The spores germinate quickly, usually after forty-eight hours. Glaeospo- rium affine is troublesome on orchids in Europe, but has not yet proved very serious in the United States. Other Orchid Glceosporiums Gloeosporium oncidii Oud.= G. maxillaria All. This organism is confined to leaves of Maxillaria infestans. GlcBosporium epidendri Heim. This organism attacks stems of Epidendrum sp. Glceosporium stanhopea AUesch. is found on leaves of Stanhopese. Glceosporium Idlitz Herm. is found on leaves of Lxlia sp. Glceosporium pallidum Karst. and Har. occurs on leaves of Liparis longipes. Colletotrichum orchidearum K. and H. appears on leaves of Bolbophyllum labbi, B. longiflorum. It is also found on foliage of Cymbidium sp., Physio- phon loddigesii; Ezia stelleta, Coelogyne mayeriana, Pleurothallis tribuloides, Sarcanthus pugioniformis, on pseudobulbs of Eulophia saundersiana and on Oncidium pulvinatum. Colletotrichum dichea Herm. grows on foliage of Dichsea vaginata. Colletotrichum roseolum Henn. develops on the pseudobulbs of Stanhopea oculata. 304 Diseases of Greenhouse Crops Leaf Spot of Orchids Caused by Cercospora angreci Roum. Symptoms. This disease is usually manifested as spots which are more prominent on the underside of the leaves. As the affected foliage turns pale and loses its green color, the spots become covered with a chocolate-colored mold. The latter growth consists of the fruiting stalks and conidia of the fungus. Cercospora angreci is found on foliage of Odontoglossum alexandrae. Little is now known of the causal organism and of methods of control. Bletia Leaf Spot Caused by Volutella concentrica Hals. Associated with the anthracnose (Colletotrichum bletia) is often found a leaf spot which may be mistaken for it. The characteristic of this disease is the formation of large dark spots (fig. 59, a.). Each spot is made up of numerous bluish-colored concentric rings. The fruitings of the fungus ap- pear as lemon-colored balls. It is not definitely known whether the Volutella fungus is an active or a weak parasite merely following some injury, or the attacks of a bacterial organism. In fact little study was given to this trouble and the only record that exists is a note by Halsted.* *HaIsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Ann. Rept.: 417, 1893. Orchid Diseases 305 Fungi Found on Orchid Leaves The following are fungi found by Hennings* on dead orchid leaves : Physalospora orchidearum Henn. This fungus is found on dead stems of orchids of Tainiae stellatje and Laelia schilleriana. It is probable that the fun- gus Physalospora herbarum (Pers.) Rab. found on dead stems of Fhajuswallichii is the same as P. orchidearum. Pleospora orchidearum Henn. This fungus is found on dried-up stems of Fhajuswallichii. Nectria (Dialonectrid) bolbophyli Henn. This fungus is found on dead pseudo-bulbs of orchids of Bolbophyllum lobbii. Nectria hehnickiana Heim. This was found on orchids imported from Brazil. Macrophama oncidii Henn. This fungus was found on dead leaves of Oncidium pulvinatum. Macrophoma cattleyicola Herm. This fimgus was found on pseudo-bulbs of Cattleya labiata. Diplodia sobralia (Henn.) Taub.t Found on dead leaves of Sobralia sessilis. Other Fungi Found on Orchids Stibella bulbicola Henn. is found on pseudo-bulbs of Gomeza plantifolia, Stanhopea spec, Sarcanthus pugioniformis, Epidendrum spec, and on Oncidium pulvinatum. 'Hennings, P., Hedwigia 44: 169-X74, 1904 t See Taubenhaus, J. J., Amer. Jour, of Bot, 8:324-331, 191S' 3o6 Diseases of Greenhouse Crops GrapMum bulbicola Henn. occurs on pseudo- bulbs of Oncidium pulvinatum. Tuhercularia cattleyicola Henn. grows on stems of Cattleya guttata. Sclerotium orchidearum Henn. develops on stems of Vanda tricolor, and Dichsea vaginata. Diplodia bulbicola Henn. Found on dead pseudo-bulbs of Gomeza planifoUa. i Zythia nepenthis Henn. Found on dead leaves of Nepenthes bicolorarta. Of the other fungi which are often found on dead foliage of Nepenthes may be mentioned Phyllosticta nepentheacearum Tassi, and Phoma nepenthis Cook and Mass. Humaria thozetti Beilkl., Excipularia epidendri Hennv Found on dead foliage of Epidendron. OxALis {Oxalis bowiei) Cultural Considerations. Oxalis is forced mainly as a window plant grown in baskets or pots. It requires a rich soil and an abundance of water. The flowers open only when exposed to full light. Fungi Recorded on Oxalis The Oxalis is a very hardy plant. The following are the fungi recorded on the host : Mcidium oxali'- dis Thuem., Darluca filum (Biv.) Cast., Fuccinia oxalidis Diet, and Ell., Urocystis oxalidis Pazs. Palm (Phcenix spp.) Cultural Considerations. Palms are very sensi- tive to wet and poorly drained pots or benches. o •J < H Palm Diseases 307 The soil best suited to palm culture is that which is made up of two-thirds rotted sod and one-third well rotted cow manure. Palms do poorly when treated with commercial fertilizers, and when its root system is disturbed, hence they should be re- potted only when absolutely necessary. Palms love partial shading (fig. 60) and a moist atmosphere. The temperature should be allowed to go below 60 degrees F. at night. The foliage should be kept free from dust. Diseases of Palms Forced palms are subject to less disease than those grown out of doors. Nevertheless, some of these indoor diseases often become very troublesome and serious. Smut Caused by Graphiola phcenids Port. Symptoms. Smut is a common disease on both greenhouse and outdoor palms of all sorts. The affected areas on the leaf become mottled with yel- low, and upon the surface pustules appear (fig. 61, a.). These are cup-shaped -conceptacles pro- duced by the causal fungus, and in which the spores are borne. The spore pustules consist of a firm, dark colored exterior wall, enclosing a more deli- cate inner covering which contains a mass of thread- like filaments on which the spores are produced (fig. 61, b.). The spore pustules become very nu- merous and the affected foliage slowly shrivels. 3o8 Diseases of Greenhouse Crops Control. All diseased material should be de- stroyed by fire. Some florists recommend spraying or sponging the leaves with potassium permangan- ate. Anthracnose Caused by Colletotrichutn kentia Hals. This disease has been first studied by Halsted* as it was found by him to attack the various orna- mental Kentias. Symptoms. The disease appears as watery spots, which soon become dry (fig. 61, h) and within which are formed the salmon-colored acervuli which contain numerous setae. In time the dead tissue falls out, leaving holes in which remain the hard, woody vessels which run across. This disease also attacks young seedlings and cripples them beyond any commercial value. The following Kentias are subject to the attacks of the anthracnose: Kentia belmoreana, K. canterburyana, and K. fosteriana. Control. It is difficult to keep this disease in check unless the infected material is removed and destroyed by fire. Spraying the plants weekly with a standard fvmgicide will keep the anthracnose in check. ExospoRiuM Leaf Spot Caused by Exosporium palmivorum Sacc. Symptoms. The disease is characterized by mi- • Halsted, B. D., New Jersey Agr. Expt St., Fourteenth Ann. Kept: 407-409, 1893. Fig. 6i. Palm Diseases. a. Palm smut, b. Palm smut fungus (after Stone and Smith), c. Exospo- rium leaf spot, d. cluster of spores of Exosporium palmivorum, e. individual spores of E. palmivorum, f. conidiophores of E. palmivorum (.d-e after Tre- lease), g. Sphserodothis leaf spot (after Smith, R, E.), h. anthracnose (after Halsted). Palm Diseases 309 nute brown spots. These are often so numerous as to involve the entire leaf, causing it to dry up and die (fig. 61, c). This trouble is very common on greenhouse palms, especially on those which are kept in too long under shade. It is common on Phcenix canariensis, on P. tenius and on P. re- clinata. The disease undoubtedly must have been introduced from Europe with imported stock. Tre- lease* observed it in America in 1897. The Organism. The sporodochia are superficial black, and dense (fig. 61, d), visible to the naked eye as a black mold. The spores are borne singly, are olive brown in color, and are many times sep- tate (fig. 61, e and f.). Control. The disease seldom occurs in well lighted and well ventilated greenhouses. Where the disease makes its appearance, more attention should be given to the ventilation, and the shad- ing should be gradually diminished. All infected material should be cut off and destroyed by fire; the plants should be sprayed with a standard fungicide. Leaf Blight Caused by Pestalozzia pdmarum Cke. Symptoms. This disease appears as transparent, dirty white spots at the tip of the leaflets or at the axils. The spots spread quickly and it is not imcommon to find numerous leaves killed, and the affected plant thereby badly disfigured. As the •Trelease, W., Kept Mo. Bot. Gard. 9: 159, 1898. 310 Diseases of Greenhouse Crops a£Fected tissue dries, the spore masses are formed on the upper part of the leaflets and appear as a black exudate. Control. Infected material should be cut out and destroyed by fire. Infected plants should not be syringed, for in this way the spores of the causal organism are spread wholesale. Spraying with a standard fimgicide is also recommended. Leaf Spot Caused by Spharodithis neo loashingtonia. The disease is mentioned by Smith* as occurring in California. The leaves become covered with small elongated, black, slightly elevated spots (fig. 61, g.). Affected leaves should be removed and burned, and the plants sprayed with a standard fungicide. Pansy {Viola tricolor). Cultural Considerations. Pansies are grown mostly out of doors. Occasionally, however, flor- ists raise them indoors as pot plants for purposes of window decoration. Its cultural requirements are about the same as for the violet (see p. 351). Diseases of the Pansy Pansies, like violets, are subject to about the same diseases. •Smitb, R. E., and Smith, £. H, California Agr. Expt Sta., Bui. 218: 1148, 1911. I — I — I — I — I — ' Fig. 62. Pansy Diseases. a to f. Colletrotrichum viola-tricoloris R. E. Smith, a. affect«d leaf- let, h. several confluent acervuli with mycelium, setx, and conidia, c. single acervulus, more enlarged, d. basidia and production of conidia, e. conidia, f. affected blossoms, g to i. Fusariwn violtr. Wolf, g. forma- tion of microconidia, h. germination of macroconidia, i. macroconidia (o-/ after Smith, R. E.; g to » after Wolf, F. A.). Pansy Diseases 311 Anthracnose Caused by CoUetotrichum viole-tricoloris R. E. Sm. Symptoms. The disease attacks the petals, and affected flowers become deformed, and fail to pro- duce seed. This is a serious consideration especially from the seedman's point of view. The spots on the leaves (fig. 62, a) are small with prominent margins. The Organism. The acervuli are numerous, the stroma poorly developed, and the setae mostly sin- gle or in pairs, short, two septate and deep brown in color. The conidiophores are short, the conidia oblong or slightly curved, with blimt ends (fig. 62, b-f.). Control. The disease is usually introduced with the seed. All shriveled seed should therefore be discarded, and the healthy ones soaked for five min- utes in a solution made of one ounce of formalde- hyde in twenty gallons of water. Diseased plants should be destroyed by fire. Pansy beds where anthracnose is present should be kept on the dry side of the house. The plants should not be sprinkled with water, as in this way the spores of the causal fungus may be spread about. Healthy plants may be protected by spraying with a standard fungicide. Leaf Spot Caused by Cercospora violes Sacc. Symptoms. This disease appears as small dead 312 Diseases of Greenhouse Crops spots surrounded by a definite black border. The spots soon enlarge and when very numerous cause the premature death of the foliage. The trouble is also met with on the blossoms; the petals in this case become spotted and blotched. Affected young blossoms become distorted or fail to open'altogether. The Organism. The conidiophores of the fun- gus are short, simple and grayish. The conidia are long, slender, rod shaped, hyaline, and many septate. Control. It is claimed by Stone and Smith* that good results were obtained by spraying with Bor- deaux. The latter, however, is objectionable be- cause of its staining the blossoms. Ammoniacal copper carbonate may therefore be used instead. Spraying may be done at intervals of every two weeks. All dead and infected material should be destroyed by fire. Root Rot Caused by Fusarium viola Wolf. This disease causes a rot of the roots and stems. The causal organism (fig, 62, g to i) is usually brought in the house with infected compost. As a control measure soil sterilization is recommended (see pp. 32-43). •Stone, G. E., and Smith, R. E, Mass, (Hatch) Agr, Eipt Sta. Ann. Kept. 11: 152, 1892. Pansy Diseases 313 Crown Rot Caused by Rhizoctonia solani Kuhn. Crown rot first appears in the form, of minute lesions at the crown of the plant. These enlarge and penetrate the tissue deeply until the plant is practically girdled. Rotting usually sets in, where- upon the prostrate branches, the leaves, and peti- oles also rot. For a description of the causal or- ganism and for methods of control, see p. 20. Pandanus or Screw Pine (Pandanus veitchii) Cutural Considerations. Screw pines are forced extensively and are used as ornamental house plants. They require a temperature of 65 to 70 degrees F. and must be exposed to full light, espe- cially in the winter. The plant flourishes best in a soil composed of two parts of heavy loam and one part of thoroughly rotted cow manure. The soil re- quired is a heavy loam to which is well worked in one-third of thoroughly rotted cow manure. Diseases of the Pandanus. Pandanus is consid- ered a very healthy plant. There are, however, two fungi that proved injurious; these are Nectria pandani Tul. and Melanconium pandani Lev., which are known to be parasites. PoiNSETTiA (Euphorbia pulcheritnaj Cultural Considerations. Poinsettias are exten- sively grown for the Christmas trade. The plants 314 Diseases of Greenhouse Crops prefer a soil consisting of fibrous loam, one-fourth of which is well rotted cow manure. Poinsettias require frequent repotting to prevent them from be- coming potbound. The night temperature should never go down below $5 degrees F. As the plants advance in age, the temperature is raised to 65 or J J degrees. A few days before Christmas the stock should be ready and the temperature lowered to 50 degrees F. Great care should be exercised to prevent the potted plants from becoming either overwatered or too dry. Poinsettias that are to be used for cut flowers should have the stem end dipped in hot water for a few moments and then placed in cold water. This procedure will cauter- ize the wounds and thus will add to the keeping qualities of the blossoms. Diseases of Poinsettias Poinsettias seem to be remarkably free from dis- eases. This is especially true as the plants outgrow the cutting stage. Collar Rot Caused by Rhizoctonia solani Kuhn. Symptoms. The trouble is confined mostly to cuttings that have been planted in an infected soil. The lesions unite and in nearly every case form a collar around the stem on the surface of the soil. The collar formed is narrow, depressed, and dark in color. For a description of the causal organism and methods of control, see p. 20. Fig. 63. Primrose Diseases. svot\^Td'UTr HalfteS""''"'" '"' ^P"*' '■ ''""■"<="°=e. d- K^'mularia leaf CHAPTER 25 PRIMROSE {Primula sinensis') Cultural Considerations. Young seedlings are greatly injured if the compost contains unrotted manure. "When the plants begin to grow rapidly a little bone meal may be worked into the soil. During the blossoming period a little weak liquid manure may be given, but only when the leaves are pale. In transplanting, the crown of the plant should not be planted too deeply in the soil lest it rot. Neither should it be planted too high lest it fall over. After transplanting primroses need shade. Later, however, they should be given the benefit of full light and ventilation. The soil should never be allowed to become dry. Diseases or the Primrose Primroses are subject to several serious diseases. Spot Decay Caused by Sclera tinia fuckeliana (De By.) Fckl. Symptoms. The conidial stage, Botrytis vulgaris, of this fungus causes a spot decay on the foliage (fig. 63, a.). The fungus often thrives on old 315 3i6 Diseases of Greenhouse Crops and faded blossoms. These, therefore, act as a source of infection. It is needless to add that clean- liness will form a part of the control method. Spraying with any of the standard fungicides is also recommended. Anthracnose Caused by Colletotrichum primultz Hals. Symptoms. AfiFected leaves become brown and spotted. The spots are more visible on the lower part of the foliage (fig. 63, c). The acervuli with its black setse of the causal organism are especially conspicuous when looked at with a mag- nifying lens. At present little is known of the organism. The disease may be kept in check by spraying with a standard fungicide. Blioht Caused by Phyllosticta primulicola Desm. Symptoms. On the leaves of the plant appear somewhat circular spots (fig. 63, b) that are brown or whitish in color with a light border, with which are found numerous pycnidia. The disease attacks various species of the genus Primula with different effects. On P. sieboldii and on P. obconia, the trouble is usually confined to the lower leaves. On P. sinensis the central part of the leaf is attacked be- fore the surrounding tissue loses its color. On P. sieboldii the leaves may often be blotched through- out, while on P. obconia one-half of the leaf is Primrose Diseases 317 often destroyed before the other half shows any marked deterioration. Little is known of the causal organism. The de- struction by fire of diseased material and spraying with a standard fungicide is recommended. Leaf Spot Caused by Ascochyta primula Wail. Symptoms. The presence of the disease is shown by oval spots, which spread and often involve the entire leaf. This disease may often be mistaken for the spotting caused by Phyllosticta primulicola. However, a microscopical examination will distin- guish the two organisms. Leaf Blotch Caused by Ramularia primula Thim. Symptoms. The presence of the disease is shown by large yellow blotches in the ashen colored cen- ters of which are borne the spores (fig. 63, d.). The Organism. The conidiophores grow on both sides of the spots, and are rarely branched, con- tinuous and sranewhat denticulate. The conidia are thick but taper towards both ends. Their structure is c(mtinuous or one septate. Control. This disease may be kept in check by spraying the plants with a standard fim^cide. In- fected material should be destroyed by fire. 3i8 Diseases of Greenhouse Crops Roses {Rosa galUca chinensis). Cultural Considerations. As soon as the cut- tings form roots which are about one-half inch in length, they should be potted. At this stage, if left too long in the propagating bench, the wood tissue of the cutting will harden and the subsequent health of the plant will be endangered. A medium water-holding capacity is an indication of a good potting soil for roses. Most greenhouse (fig. 64) varieties prefer a heavy loam. Other varieties such as the Maryland thrive best in a soil which contains a large percentage of sand. Roses are very sensi- tive and readily become injured when given partly decayed organic matter. The case, however, is dif- ferent when well rotted manure is used, for this latter food exerts a wholesome stimulating effect. The development of a good root system largely de- pends on the soil texture and on the plant food which it contains. It is necessary to stir frequently the sur- face soil of rose benches. This not only destroys weeds, but also provides aeration. However, as soon as the surface soil becomes filled with feeding rootlets of the rose plants, the cultivating should be done very superficially or should cease altogether. During active growth, the plants require an abun- dance of ventilation and a comparatively low temperature. Diseases of the Rose Greenhouse roses are subject to the attacks of several important diseases. Fig. 64. Rose House. Rose Diseases 319 The Bronzing of Leaves Cause, Physiological. Symptoms. This trouble commonly affects grafted varieties of the Tea, Bride, and Brides- maid. By some growers the disease is often mistaken for a stage of the black spot caused by Diplocarpon rose. Bronzing produces a mottled bronze color- ing of the foliage. Later the mottling becomes more prominent in the form of spots, while the ad- joining tissue turns pale yellow. Frequently the entire leaflet becomes bronzed with no yellowish color apparent. At times the affected leaflets and leaf stalks drop to the ground. The cells of the affected tissue contain an abundance of calcium oxa- late crystals, a condition that indicates poor nutri- tion. Bronzing is usually confined to two places. First, where a stem has been cut and a new branch has started the leaf at the base begins to bronze; second, where an eye or an auxiliary bud has been rubbed off, the leaf generally becomes bronzed. From studies made at the Massachusetts Station* there seems to exist a difference in susceptibility between young and old plants. Bronzing may be expected to occur on young plants. It is also prev- alent both on plants which are forced too rapidly and on weak stock. The selection of strong, hardy stocks and care in feeding will prevent the trouble from becoming serious. * Massachusetts Agr. Expt. Sta. (Hatch) Ann. Rept.: 156-1591 1899. 320 Diseases of Greenhouse Crops "^^ Blossom Blight Cause, unknown. Symptoms. The trouble manifests itself in the failure of the buds to open. At first the buds seem to develop normally. Soon, however, the outer petals wrinkle, turn yellow or straw colored, and stop growing. Occasionally the buds open par- tially, but fail to attain normal size. The true cause of the disease is unknown, although, as believed by Stevens and Hall,* it may be due to some physio- logical disorder in the metabolism of the plant. No control method is known. Crown Gall Caused by Pseudomonas tumefaciens Sm. and Towns. This disease is a very dangerous enemy to out- door roses. It has, however, proved of little eco- nomic importance to indoor roses (fig. 65, b.). For a description of the symptoms and of die or- ganism, see p. 115. J Downy Mildew Caused by Peronospora sparsa Berk. Symptoms. Downy mildew is more diiBcult to detect than the powdery mildew. It is also more •Stevens, F. L., and Hall, J. G., North Carolina Agr. Expt. Sta., Thirty-first Ann. Kept.: 78-79, 1908. Fig. 65. Rose Diseases. 0. Pilobolus crystaUinis (i) Group of sporophores, (2) specks on leaf, (3) method in which the spore bearing cap is blown off, (4) spore head magni- fied, (5) young sporophore (after Clinton), b. crown gall, c. Phragmidmm sub- coriicum (after Smith, R. E.), d. powdery mildew. Rose Diseases 321 difficult to control, because the causal organism lives within the tissue of its hosts. This mildew resembles that of the grape, potato, bean, etc. It usually appears in irregular spots. On the lower surface of the leaves, the fruiting of the fungus resembles a downy white to purple coating. It is fortunate that this disease is uncommon in the United States, and even more so under greenhouse conditions. The Organism. The conidiophores are nine times branched; the branchlets are refiexed. The conidia are pale gray, subelliptic in form. Control. The removal and burning of infected material and the spraying of the plants with a stand- ard fungicide will keep it in check. Mechanical Spotting Caused by Pilobolus crystallinus (Wigg.) Tode. Symptoms. The trouble, if such it may be called, is a small specking resembling fly speck on the leaves and flowers. There is but one case on record reported by Clinton.* It appeared on two benches in a rose house. The infected benches were heavily mulched with cow manure, while the others did not receive this treatment. A careful inquiry revealed the fact that on the two manured beds the fungus Pilobolus crystallinus was very abundant. The * Clinton, G. P., Conn. Agr. Expt. Sta., 38th Ann. Kept.: 24-25, 1 914. 322 Diseases of Greenhouse Crops spore heads of this organism (fig. 65, a) when ripe are shot off into the air and stick to any object on which they may alight, which in this case happened to be the foliage and blossoms of the roses. The mechanical spotting here referred to was caused by nothing more than the presence of the spore heads of the fungus. The trouble ceased when the fimgus no longer produced spores. The specking on the rose blossoms was not serious enough to injure their market value. Rose Rusts Caused by Phragmidium species. Rose rusts are more commonly found on plants growing in the open. These, however, may be intro- duced indoors with cuttings, or plants first started in the nursery. Phragmidium suhcorticum (Schrank) Wint. This fungus causes the true rust of roses. It is very prevalent in Europe, is of little importance in the United States. On the leaves this rust appears in small circular spots (fig. 65, c), and on the stems and petioles in large powdery masses. At first the sori or spore clusters are orange-yellow, but later turn brick red. Phragmidium speciosum Fr. This fungus is the cause of a rose rust which affects the stems and which rarely appears on any other part of the plant. The sori are black and irregularly scattered. The causal fungus is carried over from year to year as viable mycelium in the affected host. Cutting out Rose Diseases 323 or burning the diseased stems will prevent the fur- ther spread of the disease. Other Rose Rusts. There are other species of Phragmidiums which have been found by Mikio Kasai.* Among them are the following: Phrag- midium americanum (Pk.) Diet, found on Rosa dahierica; Phragmidium fusiforme Schroet on Rosa acicularis; Phragmidium Japonicum Diet, on Rosa multiflora, R. wichuriana, R. lucise; Phragmidium rose multiflora Diet, on Rosa multiflora, R. laevi- gata; Phragmidium rosa rugose Kasai, on Rosa rigosa] Phragmidium yezoense Kasai on Rosa rugosa. Powdery Mildew Caused by Spherotheca pannosa Wallr. Symptoms. Powdery mildew is a very trouble- some disease of greenhouse roses. The disease ap- pears as powdery, whitish patches on the leaves, stems, and blooms. The affected foliage fails to develop normally, becoming uneven and twisted, curled and reddened (fig. 65, d.). The Organism. On the rose the conidial or oidium stage is most frequent. The conidia are ovid, hyaline, and are borne on short conidiophores. The same fungus also causes the powdery mildew of the peach, in which case the ascus stage is most common. Control. It is believed by many florists that * Mikio Kasai, Trans. Sapporo Nat Hist. Soc. 3: 27-51, 1909- J9ia 324 Diseases of Greenhouse Crops drafts favor mildew. These statements seem to be borne out by actual observations. Mildew often starts first on rose plants facing broken panes. From these, the spores are then carried by the draft to other plants until the disease becomes thoroughly established in the house. It is, therefore, impera- tive that attention be directed to broken glass. While an abundance of ventilation is necessary, drafts of all sorts should be avoided. Mildew may also be kept in check by boiling sulphur in the greenhouse for two to three hours, twice a week. The house is closed tightly during the operation, and ordinary flowers of sulphur is placed in a kettle over a small kerosene flame, as otherwise a big flame may cause the sulphur to catch fire. Mildew may also be controlled by spraying with potassium sulphide, at the rate of one ounce of the chemical dissolved in two gallons of water. The spray is only effective when used fresh. The chemical should be kept in a tightly closed bottle. Black Spot Caused by Diplocarpon rosa Wolf. Symptoms. Black spot is often very troublesome on greenhouse roses. Attacked plants lose their foli- age and the general effect is a weakening of the plant and the formation of stunted blossoms. The spots are more or less circular, black, with a char- acteristic fringed border (fig. 66, a.). Frequently the leaf tissue adjacent to the spots becomes pale or ^' rH- Fig. 66. Rose Diseases. a. Black spot on foliage, !>-g. various stages of Diplocarpon roste (after Wolf), h. Septoria rosic (after New Zealand Ann. Rept., 1915). Rose Diseases 325 chlorotic, long before the affected leaves drop off. As the spots become old, minute specks appear within. These are the fruiting bodies of the causal organism. The Organism. The fungus of black spot has two spore stages. The summer stage (fig. 66, b) is known as Actinonema ros6o .06% 61 800 .07% 52 685 .08% 45 600 • 09% 40 532 .10% 36 480 Soap. Any good soap may effectively be used as a contact insecticide. The best soap is that which is made with caustic potash rather than with caustic soda. Soda soap washes are apt to gelatinize when cold and are made difficult or impossible to be used as a spray. Fir tree oil soap may be used at the rate of three ounces to each five gallons of water without injury to plants. Whale oil soap should be used at the rate of only one-fourth pound to each gallon of water. A stronger solution may injure tender plants. Sulphur. This is used not only as a fungicide, but also as an insecticide as well. When used as a fumi- gant, sulphur at the rate of one-third of a pound to each 1,000 cubic feet of greenhouse space will be effective. When ready to fumigate the house is closed tightly, the required amount of sulphur weighed out and divided into four equal parts on Methods of Control 385 clean paper. The sulphur is then placed in wide, deep metal pans at the bottoms of which are first placed chips which have been soaked in kerosene. The pans are solidly placed at equal distances on raised bricks in the center aisle of the house. When all is in readiness fire is set to the chips. When these begin to burn well the sulphur is spread evenly on the burning chips of each pan. As soon as the sulphur ignites, the operator should run out and shut the door of the house as quickly as possible. Sulphur fumes have an irritating and suffocating effect on man. The sulphur fumes should be allowed to act for at least twelve hours before one opens the house. The sulphur fumigation may be started at any con- venient time during the day or night. This treat- ment will destroy red spider and mildew. HydrocyaniC'Acid Gas. There seems no doubt that fumigation with hydrocyanic gas offers the cheapest and most efficient method of controlling white flies, aphids, thrips, scales, and mealy bugs. However, this method has not yet gained general popularity because of the deadly nature of the gas and its injury to plants when overdone. The best generators for the gas are one-half or one gallon glazed earthenware jars. When ordering generators it should be indicated that tops are not desired. Before fumigating it is essential to see that all broken glass is repaired, and that all cracks are care- fully stopped up. It is very essential that the cubi- cal contents of the greenhouse be accurately deter- mined. To secure the cubical contents of an even 386 Diseases of Greenhouse Crops span house compute the number of square feet in the rectangle and in the right angles, and multiply the sum of the three by the length of the house. To secure the cubical contents of a three-quarter span house multiply the sums of the areas of the rectangles, and the areas of the right angle triangles by the length of the house. In estimating the cubi- cal contents of a greenhouse it is not necessary to make allowances for the space occupied by pots or benches. Fumigation should never be attempted during high winds. It should never be done during the day and not earlier than one hour after sunset. It is never wise to fumigate when the outside weather is near the freezing point. Nor is it well to fumigate during humid nights. The best time to fumigate is when the temperature ranges from $S to 68 degrees F. The chemicals required for fumigation are either sodium cyanid (NaCN) or potassium cyanid (KCN), sulphuric acid (H2SO4), and water (H2O). Sodium cyanid is preferred. It should be free from chlorin and contain not less than 51 per cent of cyanogen. Cyanid is a violent poison. It should be stored in airtight cans and carefully labelled "Violent Poison." Commercial sulphuric acid of 66 degrees Baume or 1.84 specific gravity will answer the purpose. Upon referring to Tables 20 and 21 we see at a glance the amount of cyanid per each 1,000 cubic feet necessary to kill the particular in- sect and the amount each plant can stand. For ex- ample, if one-half ounce of cyanid as indicated in Methods of Control 387 Table 21 is used per 1,000 cubic feet of space, and if the greenhouse to be fumigated contains 15,000 cubic feet, then multiply the number of cubic feet con- tained in the greenhouse by the amount of cyanid to be used per 1,000 cubic feet, 1,500 times J/^ equals 7.5 ounces cyanid. If there is the least doubt as to the amount of gas the plant can stand without injury the initial dose should not exceed one-fourth ounce for each 1,000 cubic feet of house space. Table 20 Amounts of Cyanid and Number of Fumigations Sufficient to Destroy Various Greenhouse Pests Insects •ApHids Azalea lacewing Thrips Greenhouse white fly ... . Long scale ••Greenhouse orthezia. . , **Palm mealybug Palm aphis **Long-tailed mealybug . , Florida red scale Thread scale Aspidistra scale Soft brown scale Hemispherical scale Tessellated scale Florida fern caterpillar. . . tCitrus mealybug Ounces per 1,000 Cubic Feet H '^ 2yi 2^ 2^ 2^ 2^ 5 5 Number of Fumigations Required I I 3 3 I 2 I I 3 3 3 3 3 3 3 I 3 Intervall Between Days 10 7 to 9 31 to 38 do, do. do, do, do. do. do, do. •For the most part aphids can be controlled with one-half ounce of sodium cyanid per I, coo cubic feet, although there are a few species which are quite resistant to this gas and not so readily killed. tThe greenhouse Orthezia and mealybugs around the roots of plants are very difficult to kill, and this dosage is recommended only for those occurring above the soil. 388 Diseases of Greenhouse Crops I Hi •s .1 I ^ I §s n Sj3 SP S a ^ o o ^ e . j» 5 3 go SS^ go I Ui CIS II CO M 23 coO 9 s •i ;l: • b • ^ a < £ I » & a m Q < X n s s^ssscs ;scsiKS isssa^sscsxs; xs s u ■sl HP. Methods of Control 389 I 3 u S c o u I d d d*^ -^ o o 3 . . . . wQ o o o o go .So "oo SogJi i^^^MgQ^hgd 66666 aa f! Z ■S ! if :i 1 8 :c s • • g^JJ • g ;o 6 6 6 d S» a 8.Sg 3£ OS 3" 'S a p< .2 o »U a •s i X: X M in ■ in 10 iniQO m wi ct m g| :.§ S.g :§ «.S 9 rt o d d d-a d CS d "^.3=:^ -.a I n n b " -y- _ __ ScdcdcS s9c8 n mn muuu uu gSC-5 o, I uuu 390 Diseases of Greenhouse Crops o S I u 3 C Ci o u M M n O CO s Is 1 1 1 S O O O O 0-° B o .Bo a HZ . . . .S| o o o o g 3 o o o o o op o o o o Nl ■■? - .£ O O M •o-d ^ . 6 V i.si s£ sa E3 •IE O CiO g 1= fi£dd ga-o-o ^ :s; s ^ » S«S! S? t^SS! iSSR^S o « o « "C B ° '^ S m • • do 5 da «.a £ 2 da '•el I - *; 3 C 3 3a 8^ d d Methods of Control 391 I s a in J rid 6666666 do «13 do dodod 666 O 0) o 25 S^lz: ^ S o HZ 13 V S .S a o u +3 " 0( *a ^ .. ^ Q W ffl w <^4 *rt « d 6 6 ■CO 13 * « * eg PI 4! 1.2 392 Diseases of Greenhouse Crops H« S 04 CD bo P 36? O .&0 .Sfooo I -I »-9 ^ ^ o . to " 'tj Ig SgS-a -g-a a3&|,65|.2|dd6dS|| OS; U 3 CI 4-1 § •3-a is «i!0 ■i o SH5 a] 1^ Pi ■so 0< tSo ■S S! s;^: lO to lO s; S5 » s?s5;s« oo a S5ii on » nnnn.5£ & Methods of Control 393 2 'S'S I'S J 11 '^=" =6S 6?6S QiOi '** Ol 1 .ill 6S ^ a '° S 5° !5 Sg T3 g I 3 11 la' 111 '"lis COi-^M CO i^^tOto vknn (OCDOU^tQiQkOto m s ;:; lb oO a, ^ .3 9 l^f^ • ^l^«^ 2- "S I JR ^sscssss; 3;s: sxs »«»« l;S IJ J o ..^ 6 d o a o a.S 5 o 1-4 ti 3s 'in 1 11 394 Diseases of Greenhouse Crops T3 V .s a o u H m 3 Si O « no) .S" o (fl Q •i-3 IS ^ •2 IS ■■^ SIS m 2 Co K :s3J )?: OrHM a : a . §• bfJ3 S'C C Qi :^ « a 0) d d . . . : : :b : ■.«:_•-• • 3 a "Sis.S'a eaai fir."l§ .3.1.11 5 I S I =3 >> If ■80 §S .St«g *J5-2 551 _ - - - Methods of Control 395 1 IS 8 a B SIS 5 o e o o o o o Q o o o o o ooodSoooo^CSoodo o ^a u s .s 4-1 c 8 nil ::::::; :^ : 1 H n o.s i si •il s c ssR iRX8 3;s:s;iRs;ig;s3;3;xsx;s S3js;:s :jr3«s» saiasss 3 3'g 2 2 3 3 O O M O O O Q a a S B B fl^S V V/*\ 0) U V £L QQ^QQQH •fall a ■ •^■a EiS'a oHta -fi B « OS'S P03.2 S -^ .8'1?fi'ig,&&g.|.i -a aggo.-Eaass-l.g'SS'l . -„& ks ■^<. s a a 3 S 3 3 3 3 o B o « S ■ .; S * ? g •'s a gaaa ass SS o oo.S a? g'aS 5 sa-S'S Sa«85a B e B-o.Si B.S^5 » S ifiJ'S^ J9 396 Diseases of Greenhouse Crops T3 u a 4-1 o m n •a 4* s% i •s 6S o o tH H -o . . . . o ^ • '. u 1 £ 'SbO :| iS °l II - SI 1 i-i ■ft ; : .< . 1 E o> SfSS TftcOCOOOO'^ P 0} cS OiQUSCO^O ■^IR j: £ H » tHfH r-lfHW Eli) u a li 11 • lO ai d^ II lO ■*» ■g I g ^ |.S "j Ml 1:^ S gidSj-g .S o"" Sji'S b s^ 3 ^ i> is :ise : 1 Methods of Control 397 Mixing the Chemicals. The chemicals should be mixed as follows : For each ounce of sodium cyanid use ii/2 fluid ounces of sulphuric acid and 2 fluid ounces of water. The water is first placed in the generators, then the sulphuric acid. The cyanid is then dropped into the warm acid, and the manipula- tor must at once leave the greenhouse and shut the door tightly behind him. Short exposure with a greater strength of gas is more desirable than overnight exposure with a weaker gas. Better results are obtained when the fumigation lasts about two hours. After fumigation the house is opened at the top or at the side doors to allow the escape of the gas. During cold weather the ventilators should be opened for a short time only at several intervals. It is not advisable to fumigate if the house tem- perature is below 52 degrees F. or above 70 degrees F. As already stated, fumigation should never be done while the sun shines. Hydrocyanic acid gas is soluble in water. It is, therefore, evident that neither the plants nor the benches should be wetted before fumigation. Don'ts in Fumigation The following don'ts laid down by Sasscer and Borden will be of value to the greenhouse man : "Do not guess the amount of chemicals to be em- ployed or the cubic contents of the house. 398 Diseases of Greenhouse Crops "Do not fumigate plants in a greenhouse in day- light. "Do not fumigate when the temperature in the greenhouse is below 52 degrees or above 70 degrees F. "Do not leave the chemicals within reach of those unacquainted with their poisonous nature. Always have them properly labeled. "Do not handle the chemicals any more than is absolutely necessary. It is well to have a pair of old gloves for this, and to use them for no other purpose. Always wash the hands thoroughly after handling the chemicals whether gloves have been used or not. "Do not allow the acid to splash or drop on the clothing or skin. "Do not stay in the greenhouse any longer than is necessary to place the cyanid in the jars, and never enter a greenhouse charged with the gas until it has been thoroughly aired. "Do not fail to post danger signs at all entrances before setting off the charge, and to see that the greenhouse is closed tightly. "Do not attempt to fumigate a large greenhouse alone. "Do not fumigate a greenhouse adjoining a dwell- ing without notifying the occupants before fumi- gation. "Do not pour water on the acid; pour acid on the water. "Do not become negligent in any of the precau- tions I to do so may cause serious results." Methods of Control 399 Emulsions Kerosene Emulsion. The formula for kerosene emulsion is as follows: Kerosene 2 gallons Water i gallon Hard soap yi pound Dissolve the soap in the water by heating. Re- move the soapy water from the fire and add the kero- sene and the liquid, violently mixing until a stable milky emulsion is formed. This emulsion should afterwards be mixed with water without the kero- sene separating from it. As a spray for soft-bodied sucking insects, the above stock solution should be diluted ten to twenty times. Kerosene emulsion is not extensively used in greenhouses. Linseed Oil Emulsion. Linseed oil emulsion has been recommended by Vinal* for red spider on green- house cucumbers. The emulsion according to Vinal is made as follows: (a) The necessary articles for preparation are: 1. Bucket pump. 2. Container or mixing tank. This should hold at least eight or nine gallons. For this purpose a small washtub is perhaps the most available. Pails may be used, provided the materials are mixed pro- portionally. 3. Ivory soap. 4. Raw linseed oil. 5. Hot water. •Vinal, S. C, Mass. Agr. Expt. Sta,, Bui. 179: ^^S•l^6, 19»7- 400 Diseases of Greenhouse Crops (b) The following proportions of materials for lOO gallons of spray are used: 1. Five gallons of hot water. 2. One and one-half pounds of Ivory soap. (Six 5-cent cakes or three lo-cent cakes.) 3. One gallon of raw linseed oil. (c) Steps in the preparation of stock solution follow: 1. Put the required amount of hot water in the container. 2. Shave the Ivory soap into this and stir until completely dissolved. 3. If at this time the temperature of the soap so- lution is too hot for the hand to bear, dilute with one gallon of cold water and let it stand until about body temperature or lukewarm. The cooling of this solution is necessary in order to prepare a permanent emulsion; otherwise the oil will come to the surface on standing (see No. 6). It also prevents the chemi- cal and physical killing properties of the linseed oil from being changed by heat. 4. Add slowly, while stirring vigorously, one gal- lon of linseed oil. 5. Completely emulsify by using the bucket pump and turning the stream back into the container again, keeping the nozzle below the surface of liquid. Five minutes' vigorous pumping should completely emulsify this solution. 6. Set aside for a few minutes while preparing spray tank in order to see that oil does not come to the surface. Methods of Control 401 (d) The following are directions for the prepa- ration of spray tanks and spray: 1. Fill the 100-gallon spray tank about one-half full of water. If the water used is too cold, upon the addition of the stock solution the soap will solidify into small lumps, thus spoiling the emulsion. This may occur early in the spring, when the water is very cold, but later in the season ordinary top water may be used without danger of the soap solidi- fying on the addition of the stock solution. 2. Add stock solution made above. (See (c)| 1, 2, 3, 4, 5, 6.) 3. Agitate. (If lumping occurs, the addition of a few pails of hot water will remedy this.) 4. Fill the 100-gallon spray tank. Fungicides These poisons are used to control fungous diseases. As previously stated, some parasitic fungi live on the surface of the leaves and stems and are therefore easily controlled. An example of this is the powdery mildew. Other fungi, and these are in the larger majority, are those which live parasitically within the tissue of the host, and therefore cannot be reached by any spray. Fungicides are helpful only in pre- venting entrance of the parasite in the host. They are as ineffective in controlling insect pests as are insecticides in controlling fungous diseases. The author has often referred in this work to the term "standard fungicide." In reality there is no 402 Diseases of Greenhouse Crops one standard fungicide. The term as employed here, however, refers to any effective fungicide that is best adapted to each particular case. For instance, Bordeaux mixture may be termed "standard" if used to spray greenhouse muskmelons or cucumbers. In this case the staining of the Bordeaux would not injure the marketable product since the Bordeaux film may be readily washed or wiped off. However, Bordeaux mixture could not be termed standard for spraying roses in bloom. At that time the Bor- deaux stain may injure the market value of the bloom more than would the disease that we wish to control. In this case, therefore, ammoniacal cop- per carbonate or some other colorless fungicide may be termed standard. Bordeaux Mixtures. The strength used for ten- der plants is three poimds of copper sulphate — ^also known as blue stone, six pounds of lime, and fifty gallons of water. The easiest way to prepare it is to dissolve the blue stone thoroughly in twenty-five gallons of water. The best quality of unslaked lime should be used and slaked in a little water, care being taken, however, not to flood it while slaking, nor to let it become too dry. When the slaking is completed, enough water is added to make twenty- five gallons. The lime water and the blue stone so- lution are then mixed, pouring in first one part of lime water, then another part of the blue stone; the mixture is then strained and used at once. For crops with less delicate foliage, the standard Bordeaux mixture is 4-4-50; that is, four pounds Methods of Control 403 copper sulphate, four pounds unslaked lime, and fifty gallons of water. With greenhouse crops it is not always necessary to prepare stock solutions. Only enough for immediate use is prepared at one time. In preparing Bordeaux the following points should be kept in mind : ( 1 ) Copper sulphate solutions must be kept only in vessels of wood, fiber, brass, bronze, or copper. They must not be kept in iron or tin vessels, as they corrode them. (2) It is necessary to use fresh lime, as air- slaked lime is useless. (3) Bordeaux mixture can be used only when freshly mixed. If allowed to stand twelve hours after making, it loses all fungicidal value. (4) Bordeaux mixture or lime should never be strained through burlap. The lint of the burlap is likely to work up into the nozzles and clog them. (5) Undiluted solutions of copper sulphate or lime should never be mixed together. (6) Bordeaux mixture should not be prepared with hot water. Ammoniacal Copper Carbonate. The objection to the use of Bordeaux is that it stains the leaves and foliage. To avoid staining, colorless ammoniacal copper carbonate may take the place of Bordeaux. It is prepared as follows: Copper carbonate 5 ounces Ammonia (26° Baum^) 3 pints Water 50 gallons 404 Diseases of Greenhouse Crops The best results are obtained when the copper carbonate is first made into a paste with a little water. It is then dissolved by adding the ammonia, which is diluted with four quarts of water. If three pints of ammonia fail to dissolve all the cop- per carbonate, more may be used. Ammoniacal cop- per carbonate is only effective when used fresh. It loses its fungicidal value by standing, as the am- monia evaporates quickly. Sulphur. Flowers of sulphur are often used to control powdery mildew or asparagus rust. It may be applied either by hand or with a duster. There are a number of other fungicides on the market which are not mentioned here. They should be thoroughly tested before they are used. Combination Sprays. For purposes of economy, it is advisable to control both insect pests and fun- gous diseases at the same time. Spraying, if prop- erly done, is effective in controlling or in keeping in check all the pests which attack greenhouse crops. In combining a fungicide with an insecticide, we may accomplish two aims in one operation. The various spray mixtures which may or may not be combined are indicated by Cooley and Swingle * — Bordeaux Mixture Paris green yes yes Arsenate of lead yes yes Arsenite of zinc (ortho) yes no Arsaoite of lime yes yes * Cooley, B. A., and Swingle, D. B., Montana Agr. Expt Sta. Circ. 17: 1x9-151, 1912. Methods of Control 405 Each of these preparations is mixed and applied just as if it were used alone. A combination of the ammoniacal copper carbonate with an arsenate would be imsafe, since the ammonia renders the arsenic more soluble, and hence may result in the burning of the foliage. However, it may be safely mixed with the tobacco products. Recent investigations by Professor Safro, En- tomologist to the Kentucky Tobacco Products Co., indicates that "Black Leaf 40" may be tised with- out soap in combination with such spray chemicals as lime-sulphur, arsenate of lead, arsenite of zinc, and iron sulphate, for controlling sucking and chew- ing insects and fungous diseases. Professor Safro's work further claims that "Black Leaf 40" may be safely combined with Bordeaux, and the desired re- sults obtained. He writes as follows : "For purposes of spraying, add to every one hundred gallons of Bordeaux three-fourths of a pint of 'Black Leaf 40.' As far as safety to the foliage is concerned, much greater strength of nicotine may be added to the Bordeaux, but no additional effectiveness will be given to the mixture as an insecticide. Any nicotine solution which contains four hundredths of one per cent nicotine will be effective in controlling plant lice if the spraying is thorou^ly done." PROPORTION 'of combined SPRAYS Bordeaux and Paris Green Paris green H pound Bordeaux mixture 50 gallons Bordeaux and Arsenite of Soda fArsenite of soda i quart Bordeaux mixtxare 50 gallons 4o6 Diseases of Greenhouse Crops Bordeaux mixture must never be combined with kerosene emulsion, carbolic acid emulsion, and mis- cible oils. (d) Fotassium Sulphide. Like sulphur, this is a valuable fungicide for the control of the powdery mildew. The following strength is recommended: Fotassitim sulphide 4 ounces Water 10 gallons Potassium sulphide is effective only if used im- mediately after it is prepared. It loses its value by being exposed for any length of time. Stickers. It is well known that with some plants, such as cabbage, spray mixtures cannot be made to stick. The use of an adhesive added to the spray mixture will largely overcome this difficulty. An adhesive may be prepared as follows: Resin 2 pounds Sal soda (crystals) l pound Water i gallon The resin and the sal soda should be added to one gallon of water and boiled in an iron kettle for one and a half hours until clear. For plants which are hard to wet, such as cabbage or onions, the amount of the solution given above should be used for each fifty gallons of Bordeaux or ammonia- cal copper carbonate. For other plants, this amount is added to each one hundred gallons of the spray mixture. Fig. 8i. Bucket Spray Pump with Long Nozzle. Methods of Control 407 Principles Involved in Spraying It should be remembered that to destroy chew- ing insects, such as caterpillars, etc., the stomach poison must be evenly distributed all over the plant. This thorough spraying should be done as soon as the presence of the pest is suspected. Intelligent and observant growers will remember the time of appearance of the pest every year, although this date depends somewhat on the climate of each season.' In destroying the green aphids, the contact poison, should be distributed as evenly as possible on the insect itself. It is, therefore, best to spray for aphids when they are actually found working on the plants. To check chewing insects and fungous pests, how- ever, the applications are made before the parasites appear. Before spraying it is necessary to have well in mind which organism is to be destroyed, and the proper ingredients to be used. To keep fungous pests in check it is necessary to have the plant covered with the fungicide all the time infec- tion is feared or suspected. This spraying is preven- tive, protecting the plant from becoming infected. When the parasite has penetrated the host, spraying is of little value in saving the infected plant, al- though it will protect others which are as yet healthy. It is essential that the gardener be always ready to spray. Sometimes delay for even a day may prevent the attainment of positive results. The timely destruction of one insect, or of one spore, 4o8 Diseases of Greenhouse Crops means the elimination of countless generations of these pests. Thoroughness is as important in spraying as it is in everything else in life. Especially is this true for the control of fungous diseases. Spraying Machines Success in spraying often depends on the sprayer, and especially on the nozzle. In small scale such as under greenhouse conditions, it is next to useless to invest in elaborate expensive machinery. A small bucket pump with long nozzle (fig. 81) as used by Professor Paddock of the Texas Experiment Station has given good satisfaction. The Auto Spray No. 1 is a very desirable spraying machine for indoor plants. Hygienic Considerations Since plants are endowed with life they readily respond to intelligent hygienic treatment. This is especially true with indoor plants, which at best are growing under abnormal conditions. Every effort should, therefore, be made to create indoors as nearly normal conditions as possible. The effect of proper sunlight, heat, moisture and ventilation has already been discussed under pages 53-85. Cleanliness is also an important consideration. The walks, interior walls and glass should be kept as clean as possible. Old and used pots should be scrubbed and washed at least once a year. Dead or infected plants should Methods of Control 409 never find their way on the manure pile. Such manure is bound to find its way back and will con- taminate the soil in benches and involve later extra expenses of soil sterilization. Insects and diseases should never be allowed to get a strong foothold. It is easy enough to destroy a few aphids for instance, but it becomes a matter of greater difficulty to han- dle a greenhouse which has become thoroughly in- fested. No definite rules can be laid down, but every greenhouse man must study his crops and his conditions in order to succeed in keeping his plants in the best condition of health. Selection of Cuttings With forced crops, perhaps more than with any others under glass, the success of cuttings is largely dependent upon proper selection. This is true for instance with carnations, roses, violets or chrysan- themums. It would scarcely seem possible that the nature of the cutting could materially influence the future plant. This, however, is a fact which has been aptly mentioned by Galloway.* It must be remembered that plants, like animals, are influenced by inheritance as well as by environment. In se- lecting cuttings the object should be to procure those parts of the plant which will transmit with the greatest vigor the ability to flower or to fruit as the case may be. Experienced growers will appreciate this. Frequently in starting with two-rooted cut- • Galloway, B. T., Year Book, U. S. Dept. Agr., 247-2561 i*9S- 410 Diseases of Greenhouse Crops tings from the same plant, grown under the same conditions, dissimilar plants are produced. The one may be vigorous, blooming freely, while the other may be dwarfed and sickly, and produce no flowers, or merely a few of an undesirable type. In the selection of cuttings, appearance alone should not constitute the main guide. A cutting may ap- pear vigorous, yet be immature or too old. Violet cuttings made from old wood will generally pro- duce inferior plants, which will run out within a year or be carried off by disease. Violet cuttings made from soft, immature wood, will result in weak, spindly growth and in plants susceptible to damping off. On the other hand, a cutting may be made of the proper material, yet if it is too short it will also be useless. A violet cutting that is too short will not have sufficient anchorage. Each time a flower is pulled it will roll around or its roots will break (fig. 82, a to c). Not only is care necessary in the selection of cuttings, but it is also necessary to provide proper conditions for growth. A setback at this time may result in disappointing returns later. Heat, air, light and water should be carefully attended to in dealing with soft-wooded cuttings. GLOSSARY AcERVULUS (Acervuli). A non-sexual, open cup-shaped fruiting body of fungi. ^ciDiospoRES. Spores of rusf fungi borne in an iEcidium. iEciDiUM (iEcium). A cup-shaped body in which are formed the spring spores of certain rust fungi. Aerobe. Micro-organisms requiring air, more especially oxygen. Ammonification. The formation of ammonia at the ex- pense of other forms of nitrogen compounds, accom- plished through the action of soil micro-organisms upon organic substances. Ammonifiers. Soil micro-organisms which are capable of transforming nitrogen compounds into ammonia. Am(EBOID. Like an amoeba, the creeping movement of which is made possible by appendage-like bodies. Antheridium. The male sexual organ of fungi. Apical. Terminal formation at the point of any fungous structure. Ascospore. Spore borne in an ascus. Ascus (Asci). Winter sexual spore sac, within which are formed the ascospores. Arthrospores. Whole vegetative cells of either bacteria or fungi which, by a thickening of their walls, become resting spores. B Bacterium (bacteria). Simplest form of plant belonging to a low order, lacking chlorophyll, and reproducing by means of fission. 411 412 Glossary Basidiospores. Spores formed on basidia. Basidium (basidia). A straight stick-like spore bearing fungous thread. Canker. Definite dead area in the bark of stems or roots of plants. Capitate. Possessing a head. Carbonaceous. Dark to black colored. Chlamydospores. Resting spores of fungi possessing thick walls and formed within mycelial cells. Chlorophyll. Green coloring matter in leaves of higher plants. Cillate. Fringed with hair. CiLiUM (Cilia). Thread-like appendages on bacteria or zoospores of myxomycetes, which aid in their movement. Columella. Sterile axle of a pillar-like structure within a sporangium. CoNiDLA (conidium). Spores formed asexually on free borne conidiophores. CoNiDiOFHORE. A spore bearing fungal stalk. Cuticle. The outermost skin of plants. Cyst. Incrusted body. D Deliquescent. Dissolving or melting. Diffuse. Loosely spread. Dilated. Enlarged. E Endospore. Spore formed within another cell. Entomogenous. Fun^ living parasitically on insects. Enzyme. An organic chemical product capable of bringing about changes, but without itself undergoing any change or entering into the final product. ExospoRE. Outer covering of a spore. Glossary 413 Falcate. Sickle shaped. Flagella. Whip-like appendage of bacteria or swarm spores. Fungus (fungi). Plant of very low order with vegetative growth (mycelium), reproducing by means of sexual and non-sexual spores. Glaucus. Sea green. GoNiDiA. Algae-like cells. Guitulate. Drop-like. H Haustoria (haustoriumj. Special organs of fungi used for attachment or for obtaining food. Host. Any plant which nourishes a parasite. Hyaline. Translucent or colorless. Hypertrophied. Any part of diseased plant abnormally enlarged. Hypha (Hyphae). Thread-like vegetative part of fimgi. Indurated. Hardened. Infect. To cause disease. Intercellular. Growing between the host cells. Intracellular. Growing inside the host cells. Lenticel. a special loose corky structure in plants in- tended to serve as a medium of exchange of gases. Lesion. A definite diseased area. 414 Glossary M Macroconidia. Large conidia. MiCROCONiDiA. Very small conidia. Middle-lamella. The connecting or cementing membrane between any two cells of a plant. Mycelium. Vegetative threads or hyphse of a fungus. Mycology. The study of fungi. O Omnivorous. Attacking a large variety of plants. Oogonium. Female sexual organ of fungi containing one or more oospheres. OosPHERE. Naked mass of protoplasm developing into oospores after fertilization. Oospore. Fertilized oosphere. Papillate. Possessing wing-like structure. Paraphyses. Sterile filaments found in some fruiting forms of fungi. Parasite. An organism living at the expense of another (the host). Pathogenic. Producing disease. Pedicillate. Borne on a stalk. Perithecium. a flask-shaped or globose, sexual frmdng body containing asci. Peritrichiate. Flagella formed all over the surface of an organism. Fionnotes. An effuse conidial stage, containing a max- imum of conidia, and a minimum of aerial mycelium. Plasmodium. A mass of naked protoplasm with numerous nuclei, capable of amoeboid motion. Polar flagella. Flagella borne at the pole ends of a micro-organism. Glossary 415 Protoplasm. The living substance of any plant cell. PsEUDO. False. Pustule. A blister or pimple. Pycinidia. Sack-shaped fruiting bodies of a fungus in which the pycniospores or summer spores are formed non-sexually. Pycniospores. Non-sexual summer spores borne in pyc- nidia. Saprophyte. A micro-organism living on dead organic matter. ScLEROTiUM (sclerotia). Compact mass of mycelium in a dormant state, living over from year to year. Septum. Any partition between two cells in the same fun- gous filament. Set^. Bristle-shaped bodies of fungi. Soil flora. Bacterial or fungus growth of a soil. SoRUS. Heap of spores. Sporangiophore. Stalk bearing sporangium. Sporangiospores. Spores formed in a sporangium. Sporangium. Free, non-sexual bearing spore sack. Spore. A cell capable of reproducing a plant like its parent. It corresponds in function to the seeds of higher plants. Stomata. Minute openings in the stems, leaves or fruits of plants which serve as a medium of exchange of plant gases. Stroma. A spore-bearing cushion composed of mycelium and sometimes of host tissue. Swarm spores. Spores possessed with the power of mo- tion, or motility. Teleutospores (teliospores), resting or winter spores of rust fungi. Telium. a sorus in which teleutospores are borne. 4i6 Glossary u Uredospores. Summer spores of rust fungi. Vesicular. Composed of vessels. Viscid. Sticky. Z ZooGLCE^. Colony imbedded in a gelatinous bed. ZoospORANGiA. Sporangia, which produce zoospores. Zoospores. A motile spore. INDEX Acid soils, treatment, 30 Actinonema rosae, 325 Actinomyces chromogenus, 115, 174 Adams, 5 Adianthum cuneatum, 254 farleyense, 254 gracillinum, 254 Aecedium cinerariae, 243 euphorbiae-gerardianae, 225 oxalidis, 306 rubellum, 176 African marigold,^ 208 Agaricus campestris, 159 All Riza, 265 Alkali soils, 31 control, 32 Alsophila Australis, 254 Alternanthera, 200 amena, 65 cultural considerations, 200 diseases of, 200 leaf blight, 200 root rot, 200 Alternaria brassicae, 129 brassicae Tar. nigrescens, 157 dianthi, 229 violae, 359 American Beauty Rose, 75 Ammonification, 13 Ammoniacal copper carbonate, 403 Anaesthetics, 89 Anthostomella achtra, 2i6 Antirrhinum, 201 anthracnose, 203 branch blight, 204 blight, 205 cultural considerations, 201 diseases of, 202 root knot, 205 rust, 202 Antirrhinum, wilt, 205 Ants, 376 Aphelenchus olesistus, 25 Aphids, 371 Aphis gossypii, 137, 372 Apium graveolens, 129 Arachnides, 365 Arsenite of zinc, 382 Arthur, J. C, 222, 223, 237 Ascochyta aspidistrae, 206 chrysanthemi, 241 fibricola, 243 hortorum, 143 lycopersici, 189 pisi, 169 primulae, 317 rhei, 176 violae, 357 Asparagus, 108 cultural considerations, 108 damping off, 108 diseases of, 108 officinalis, 108 rust, 109 Aspidiatus nerii, 371 Aspidistra, 205 anthracnose, 206 cultural considerations, 205 diseases of, 2o6 leaf spot, 206 lurida, 205 Aspidium falcatum, 258 Asplenium nidus-avis, 26 Aster, 207 cultural considerations, 207 diseases of, 207 damping off, 211 leaf blight, 208 root knot, 211 -white grub injury, 210 wilt or stem rot, 209 Atkinson, G. F., 17, 231, 257 417 4i8 Index Available nitrogen and absorp- tion of, 12 Azalea, 211 cultural considerations, 21 x diseases of, 2I2 indica, 211 leaf spot, 212 Bacillus aroideae, 280, 281 asteracearum, 208 caratovorus, 126, 281 caulivorus, 263 coli-communis, 13 cypripedii, 295, 296^ fluorescens liquefaciens, 13 fiuorescens putidus, 13 hyacinthi sepiicus, 267 janthinus, 13 lathyri, 338 megatherium, 13 messentericus Sphaerella caladii, 214 gardeniae, 260 pinodes, 168 Spherodithis neo luashingtomae, 310 Spinach, 30, 67, 177 anthracnose, 179 cultural considerations, 177 diseases of, 177 downy mildew, 178 malnutrition, 177 Sporonema, 254 obturatum, 254 Sporotrickum anthrophilum, 228 poae, 228 Spraying, 381 Spraying machines, 408 principles involved, 407 Steam rake method, 36 Stemphylium ericoctonum, 254 Stevens, F. L., 241, 320 Stibella bulbicola, 305 Stickers, 406 Stomach poisons, 382 Stone, G. E., 53, 97, 105, 134. 312 Stone, R. E., 183, 169 Stoneman, B., 310 Stout, A. B., 348 Striped cucumber beetle, 102 Stewart, F. C, 204, 213, 225, 228, 328 Stewart, V. B., 332 Stuart, W., 5 Sturgis, W. C, 232 Subirrigation, 83 effect on crops, 84 Suffocation, 83 Sulphur, 384, 404 changes of, 14 Sunburn, 94 Sweet pea, 334 anthracnose, 343 bud rot, 338 Chaetomium root rot, 344 Sweet pea, collar rot, 340 cultural considerations, 334 diseases of, 334 downy mildew, 339 Fusarium wilt, 344 malnutrition, 335 mosaic, 338 physiological troubles, 334 powdery mildew, 341 root knot, 347 root rot, 346 spot disease, 342 stem rot, 340 streak, 338 Thielavia root rot, 341 wilt, 22 Swingle,' D. B., 404 Syringa vulgaris, 27s Taft, L. R., 84 Tarsonemus pallidus, 366 Taubenhaus, J. J., 103, 305, 334 Temperature, relation to green- house, 74 Tetranychus, bimaculatus, 365 Thielavia basicola, 167, 341, 345 Thrips, 369 Tile method, 37 Tobacco, 383 decoction, 383 Tolaas, A. S., 162 Tomato, 180 anthracnose, 191 black mold, 194 black rot, 193 blossom end rot, 183 broom rape, 195 buck eye rot, 188 cultural considerations, 180 damping off, t86 fruit rot, 189 hollow stem, 181 injured by fumigation, 199 late blight, 186 leaf mold, 192 leaf spot, 189, 190 mosaic, 183 Rhizoctonia fruit rot, 195 root knot, 195 Index 429 Tomato, sleeping sickness, loi, 193 Southern wilt, 185 sunburn, 1S4 winter blight, 182 Trelease, W., 309 Trichoderna koningi, 13 Trichosporium fuliginosum, 254 Tubercularia cattleyicola, 306 Truffant, G., 294 Tulip, 348 blindness, 348 bulb rot, 349 cultural considerations, 348 diseases of, 348 rust, 349 Sclerotium rot, 350 smut, 349 Tulipa suaveolens gesneriana, 348 Tylenchus dipsaci, 271 Uredo behnickiana, 297 cannae, 216 onicidii, 297 Urocystis oxalidis, 306 violas, 353 Vromyces Setae, 119 caladii, 214 caryophyllinus, 224, 232 scillarum, 272 Urophlyctis leproides, 119 Vstilago tulipae, 349 vaillaniii, 272 Vanda, culture of, 293 Veihmeyer, F. J., 163 Ventilation, 85 Fermicularia polygoni-virgin- ica, 176 concentria, 252 Vinal, S. C, 399, 366 Viola odorata, 351 tricolor, 310 Violet, 351 anthracnose, 356 Cercospora leaf spot, 3£i crown rot, 354 cultural considerations, 351 diseases of, 352 downy mildew, 353 leaf spot, 3S7 mold, 3S3 root rot, 3S2, 354, 361 rust, 353 speck anthracnose, 358 spot disease, 359 white mold, 258 Volutella dianthi, 231 Waksman, L. A., 10, 13 Wallflower, 362 cultural considerations, 362 Ward, M., 17 Warren, G. F., 199 Water requirements, 73 Wheeler, H. J., 5 White fly, 371 White fly fumigation, 199 White grubs, 375 Wireworms, 375 Wooden beds, prevention of rot, 84 Wood lice, 377 Woods, A. F., 223, 279 Wolf, F. A., 325, 362 Zygodesmus albidus, 358 Zythia nepenthis, 306 '''''V(liii!^;iti;!!'|»iPi