Class OJI.i. Book. ^ 5? GopyiightN^. Ci}E3a{IGKT DEPOSIT. DISEASES OF ECONOMIC PLANTS THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO • DALLAS ATLANTA • SAN FRANCISCO MACMILLAN & CO., Limited LONDON • BOMBAY ■ CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA. Ltd. TORONTO DISEASES OF ECONOMIC PLANTS ^ BY f/l/^STEVENS, Ph.D. PROFESSOR OF PLANT PATHOLOGY IN THE UNIVERSITY OF ILLINOIS AND J. G. HALL, M.A. FORMERLY ASSISTANT IN VEGETABLE PATHOLOGY IN THE NORTH CAROLINA AGRICULTURAL EXPERIMENT STATION REVISED EDITION BY F. L. STEVENS THE MACMILLAN COMPANY 1921 All rights reserved §13731 OoPYBiQHT, 1910 and 1921,* , By the MACMILLAN COMPA-NY. Set up and electrotyped. Published September, 1910. Revised Edition, January, 1921. JAN 19192! « ©CU605427 PREFACE The present edition of this text-book is designed primarily for college students, but it is hoped that it may serve also as a useful handbook for others who may wish to recognize plant diseases or to apply treatments. It aims to give a comprehensive view of the field and its importance, with diagnostic symptoms and suggested treatment of all of the more important diseases prevalent on the crop plants of the continental United States with brief notes or mere mention of those less serious. A few of the more important diseases not of the United States are also discussed briefly. Diag- nostic characters are limited in the descriptions to those that may be recognized without the aid of the microscope. For further discussion of morbid histology, or of the morphology of the parasites concerned, the reader is referred to other books on these subjects. Descriptions and discussions of treatment are as full as the space admits and the reader who desires more complete information is referred to the pertinent literature cited. Since conditions are so diverse as to geographic loca- tion, climate, and soils the treatment here suggested must be more or less general. Crop growers should in all cases endeavor to secure from the nearest Agricultural Experi- ment Station the information best applicable to local con- ditions. The segregation of certain diseases under the caption ''Minor diseases" is arbitrary and it is quite possible that diseases here included may locally or seasonally be of major importance, and conversely that certain major diseases may be of but minor importance. The aim, however, is to in- dicate to the student those which in general are less wide- spread or less likely to be serious. Ample cross references are vi Preface given to render tlie information more accessible and to avoid repetition. The common names selected are those that are in general use. Diseases due to insects comprise a group which involves knowledge of the classification of insects and of their life- habits. Such diseases are set aside in the special field of the Entomologist and are not here treated. The diseases due to adverse inanimate environmental conditions, the sickening of plants due to lack of soil fertility, to excess of some element, to overabundance or lack of water or to im- proper physical condition of soil, etc., are recognized as properly belonging in the field of Agronomy and are treated in this book only in exceptional cases. During the decade that has elapsed since the publica- tion of the first edition there have come into prominence in the United States numerous diseases at that time un- known in America. Therefore the present edition includes discussion of several scores of diseases of major importance, some of minor importance, as well as many modifications of treatment that did not appear in the earlier edition. The author desires to express his especial thanks for aid in the preparation of this volume as follows: To R. J. Haskell of the Plant Disease Survey of the U. S. Depart- ment of Agriculture, who has kindly read the proof with particular reference to the usage of common and scientific names and as to the estimates of losses and statements regarding geographic distribution; to H. W. Anderson of the University of Illinois for valuable aid in the preparatiofi of the sections treating of fruit disease; to E. C. Stakman of the University of Minnesota in connection with the cereal diseases; to G. L. Peltier of the Alabama Experiment Station and W. A. Ruth of the University of Illinois for the preparation of special articles. F. L. Stevens. Urbana, Illinois, August, 1920. CONTENTS Historical ...... Damage Caused by Plant Diseases Prevention or Cure of Plant Diseases Methods of Prevention General Diseases Diseases of Special Crops Pomaceous Fruits . Drupaceous Fruits . Small Fruits . Tropical Fruits Vegetable and Field Crops Cereals .... Cereal Smuts in General Cereal Rusts in General Anthracnose of Cereals Special Diseases of Cereals Forage Crops . Fiber Plants . Trees and Timber . General Diseases Special Hosts . Ornamental Plants . General Diseases Special Diseases Fungicides . . Spraying Apparatus Soil Disinfection Bibliography Index .... vu page 1 10 13 14 19 31 31 74 102 135 149 266 266 275 280 280 321 343 354 354 381 406 407 408 440 452 460 467 491 DISEASES OF ECONOMIC PLANTS DISEASES OF ECONOMIC PLANTS HISTORICAL 1, 2, 26, 27 The science of Plant Disease or Phytopathology was ir its early formative period between 1853 and 1870, the foundations being laid in the pioneer work of Berkeley, De Bary and the Tiilasne brothers in establishing the parasitism of the fungi, and in Pasteur's fundamental work on Bacteria and Spontaneous Generation. To be sure some of the most conspicuous diseases had long been known by sight. Blight and mildew were re- ferred to in both the Old and the New Testament. Wheat rust was mentioned by Aristotle, 350 B.C. and reference to mildew is found in King Lear, Act III, Sc. 4. There was legislation even regarding wheat rust as early as 1660. However, there was little or no real knowledge of plant diseases in those times, beyond the fact that various diseases existed, and this knowledge was shrouded in superstition. Following the pioneer publications of Berkeley, De Bary, and the Tulasne brothers came the more complete treatises of Kuehn (1858), Hartig (1874), Frank (1880, 1895), Sorauer (1874, 1886, 1908), Kirchner (1890), Tubeuf (1894), Prillieux (1895), Delacroix (1902, 1908, 1911), Ward (1896, 1901, 1909), and others. It was not until 1873 that plant pathology became a part of instruction in botany, and not until 1875 that special courses in pathology were given in any of the schools of America. A series of papers begun by Burrill in 1873, another by Farlow in 1875, and other publications by Bessey, con- 1 Diseases of Economic Plants T. J. Burrill, 1839-1916 B. D. Halsted, 1852-1916 C. E. Bessey, 1845-1915 G. F. Atkinson, 1854-1918 Historical 3 tributed to the knowledge of plant disease and served especially to awaken interest in the problems of, and to at- tract students to, this field of research. In 1879 Burrill, working upon the blight of the pear and apple, was the first to attribute a plant disease to bacterial origin. His work was confirmed and his conclusions more fully established by Arthur. During the seventies, from two or three workers in this field, the number rapidly grew, augmented in the middle eighties by the introduction of plant pathology into the Agricultural Experiment Stations and the United States Department of Agriculture, until the number of papers published in the United States upon plant pathology be- tween 1888 and 1900 is estimated at over four thousand. While only a few dozen plant diseases had been even cursorily described in the United States prior to 1880, in 1910 a total of some 525 diseases, of which more than 250 were serious, had been carefully investigated and the number since that date has been greatly increased. Historical concerning plant-disease prevention.^' ^^^ Though little could be done to devise rational methods of combating plant diseases until their causes were known, a very few rule-of -thumb, empirical ways of meeting them had been suggested in very early days. As might be ex- pected, many of the methods used were valueless. Thus Parkinson early in the seventeenth century advocated the use of vinegar to prevent canker on trees, and Forsyth in 1790 gave the following directions for making a mixture to ''cure disease, defects, and injuries of plants."^ ''Take one bushel fresh cow dung, one half bushel lime rubbish from old buildings, one half bushel wood ashes, one sixteenth bushel pit or river sand. The last three are to be sifted fine before they are mixed. Then work them well together with a spade, and afterward with a wooden beater until the stuff is very smooth, like fine plaster used for the ceilings of rooms." Soapsuds or urine was used to make the composition of the consistency of plaster or paint. After being applied it was 4 Diseases of Economic Plants covered with a sifting of powder made of "dry powder of wood ashes, mixed with the sixth part of the same quantity of the ashes of burnt bones." Fig. 1. — Erwin F. Smith of the United States Department of Agriculture. Among the early chaff, however, there were some grains of wheat. Thus Riedel in 1751 advised excision followed by grafting wax for canker, and Robertson in 1821 said: ''Sulfur is the only specific remedy that can be named for the treat- Historical 5 ment of mildew on peaches. It should be mixed with soap- suds and then applied by dashing it violently against the trees by means of a rose syringe;" thus advocating a rem- edy which, modified, is still prominent for this class of diseases. The aggressiveness of several plant diseases in Europe between 1878 and 1882, particular^ the downy-mildew upon the grape, which, about 1878, had invaded Europe Fig. 2. — Millardet, 1838-1902, father of the Bordeaux mixture. Professor at the Univer- sity of Bordeaux. from America, stimulated a search in the former country for effective spraying mixtures. Trials of many chemicals were made, but it was left to accident to suggest, and to the genius of Millardet, of Bordeaux, France, to perfect, the happy combination of lime and bluestone that we now know as Bordeaux mixture. It was customary in certain vineyards to sprinkle a few rows of grapevines near the road with a mixture of milk of Kme and bluestone to give 6 Diseases of Economic Plants them a poisonous appearance to ward off depredation of the hungry passer-by. The vines so treated in 1882 were noted by Prillieux and Millardet to be less injured by the mildew than were other vines, and they ascribed the beneficial effect to its proper cause, the Hme-bluestone mixture. While several investigators were engaged simultaneously in experimenting with these chemicals upon the mildew, it was Millardet who first planned and executed experi- ments and published results which demonstrated the com- mercial value of the lime-bluest one treatment. The first systematic applications of copper, and of copper with lime as a disease preventive, were made under the direction of Millardet, August 18, 1883. In 1884 the work was repeated, and in 1885 Millardet published the first directions for preparing Bordeaux mixture : Water . .... 130 liters (34 gallons) Bluestone ..... 8 kilograms (17.6 pounds) Lime ..... 15 kilograms (33 pounds) This mixture was to be shaken upon the plants with a broom. Following this demonstration came the introduction of an era, not yet at an end, of active experimentation with fungicides, wet and dry, which has already yielded results of incalculable value. In 1885 also appeared for the first time the Ammoniacal Copper Carbonate proposed b}^ Professor Audoynaud of the Montpelier Agricultural School. Saunders, in the Canadian Horticulturist in 1884, sug- gested the use of several liquid spraying mixtures for apple scab, but little if any liquid spraying for plant diseases" was done in America prior to 1885. In 1885, from the Section of Mycology, Division of Bot- any, United States Department of Agriculture, appeared an article by Lamson-Scribner, giving directions for making "the copper mixture of Gironde," the primitive Bordeaux Historical mixture. In 1886 the spraying campaign may be said to have been well started in this country. The disinfection of seeds by bluestone was practiced first with the cereals as early as 1807 by Prevost of France, and improved by Dreisch in 1873, by the addition of a limewater bath to follow the bluestone. In 1887 Jensen of Denmark improved upon these methods by developing his hot-water treatment, which has since proved of great value, not so much for its primary use, in which it has been superseded by formalin, but owing to its applicability to those loose smuts which cannot be successfully treated by surface disinfection. Similar seed treatments have been extended to the potato by Bolley, and to cabbage by Harding. The production, by breeding, of new and disease-resistant varieties is one of the latest and most promising methods of combating plant diseases. Grapes resistant to Phylloxera were produced by Millardet; cotton, cow- peas, and watermelons resistant to wilt by Orton; cabbage by Jones; tomato by Durst and others; tobacco resistant to Thielavia by Johnson. No small part in the progress that has been made in the prevention of plant disease is due to the improve- ment of appliances, dusters, pumps, nozzles, etc., for dis- tributing the disinfectants upon the plants. This progress is well illustrated by comparing the broom of Millardet with the knapsack, barrel, or power sprayer of to-day. Fig. 3. — An improved brush for distributing Bordeaux mixture. After Lodeman. 8 Diseases of Economic Plants Important Events in Plant Disease History Ancient, Recognition of the existence of plant diseases in early Biblical times. 1683 The discovery of bacteria. Loewenhoek. 1807 The efficiency of copper against smut spores discussed. Prevost. 1821 The use of sulfur as a fungicide recommended. Robertson. 1845 The use of boiled sulfur and lime for mildew advocated. 1846 The studies of Rev. M. J. Berkeley. 1853 The beginning of the ''Morphology and Physiology of the Fungi" and the proof of parasitism of fungi. De Bary. 1861 The publication of the first American paper on plant pathology. Engelmann. 1860-1864 The founding of bacteriology. Pasteur. 1864 The proof of alternation of hosts, heteroecism. De Bary. 1869 The first university publication in America regarding plant pathology. University of Illinois. 1873 Plant pathology taught incidentally with botany in America. Burrill. 1875 Plant pathology first taught as a special subject in America. Farlow. 1879-1880 Proof of bacterial disease in plants. Burrill. 1880 The discovery of the cyclone principle in nozzles. Barnard. 1882 The beginning of "Sylloge Fungorum." Saccardo. 1884 Systematic introduction of plant pathology into American Agricultural Experiment Station work. Arthur. 1885 The announcement of the Bordeaux mixture. Millardet. 1885 Organization of a Section of Mycology in the Division of Botany, United States Department of Agriculture. Lam- son-Scribner. 1886 Proof that mosaic is infectious. Mayer, 1887 The hot-water treatment for smut. Jensen. 1888 The introduction of formalin as a disinfectant. Trillat. 1888 Organization of the State Agricultural Experiment Stations. 1890 The beginning of pump improvement for spraying. 1894 Establishment of the fact that biologic races exist. Eriksson. Historical 9 1906 The passage by Congress of the Adams Act. 1906 The introduction of the use of Hme-sulfur. Cordley. 1907 EstabHshment of the first university department of plant pathology. Cornell. 1909 The organization of the American Phytopathological Society. 1912 The passage by Congress of the Plant Quarantine act. DAMAGE CAUSED BY PLANT DISEASES The crop grower often suffers much damage from plant diseases, entirely unconscious of the fact that his crop is affected by disease. Or, if the presence of disease is recog- nized, the amount of damage is often underestimated. Thus the presence of oat smut to the extent of 15 or even 40 per cent, is sometimes entirely overlooked by an otherwise ob- servant man. An attitude of willful disbelief in the prevalence of a disease is often couched in such terms as these: "I don't see why I must work to protect my apples from rot. My grandfather used to raise fine apples without any attention to these things." It must be recognized that plant diseases are with us; that they are increasing by importation from other coun- tries or other states; that diseases formerly insignificant are, in many instances, becoming serious; that long, inten- sive culture of one crop in a locality permits new diseases to develop. Diseases have many means of dispersal; on seed, hay, or other produce shipped by mail, express, or freight; on animals; by wind; by water; by birds. Diseases will continue to spread and to increase in destructiveness until the individual and the general public are aroused to such active appreciation that conditions of plant sanitation and plant protection become much more general and effective than they now are. Conspicuous examples of the advent of diseases in coun- tries where they were before unknown, are afforded by the following: grape powdery-mildew, native to America and first seen in Europe in 1845; the American gooseberry mildew, first found in Europe in 1900; the potato late-blight, native to South America, noted in Europe in 1830; the asparagus rust, introduced from Europe about 1896; the hollyhock 10 Damage Caused by Plant Diseases 11 rust introduced about 1886; the white-pine bhster-rust introduced from Germany shortly prior to 1906; the chestnut bark-disease, introduced from the Orient about 1904. Other examples are cabbage club-root, potato-wart, grape an- thracnose, grape black-rofc, the carnation rust, and citrus canker. Cases of interstate migration of plant diseases are numer- ous, ^^^ most prominent being, perhaps, the asparagus, holly- hock, carnation, and chrysanthemum rusts, and the pear- blight. Fungi introduced into new environment, into a new con- tinent, for example, owing to the change in biologic equilib- rium, to the absence, perhaps, of their natural enemies or to readier access to susceptible hosts are often much more de- structive than in the countries from which they came. This fact finds illustration in many of the diseases mentioned above, notably so in the case of the chestnut bark-disease. Aside from diminishing the value of the produce and the thrift and future productiveness of perennials, as trees, vines, etc., plant diseases entail depreciation in the value of land, and in some cases even occasion large loss of life. Thus the famine in Ireland in 1845 is directly traceable to the injury done to the potato crop by the potato late-blight. The presence of ergot in grain used as food for cattle or man results in disease and death. The presence in land of the causal germ of the melon, cowpea, cotton or tobacco wilts, of onion smut, cabbage club-root or black-rot, or of any one of many other soil-borne pathogenes precludes the possibility of successful culture of the susceptible plant for a long period of years, perhaps forever, upon the soil in question. Such restriction may prevent the raising of the crops that are most profitable in a particular section, and in some instances depreciation of 50 per cent or more in the market value of land has resulted from the invasion of one of these ineradicable soil pests. Still more serious is this kind of injury if the crop in ques- tion is one which requires large money outlay before the 12 Diseases of Eco7iomic Plants presence of the disease germs is manifest. In the case of Sumatra tobacco under shade, or lettuce grown under canvas, the money expended to prepare for the crop may aggregate from $700 to $1000 or even more per acre the first year. The capture of such acreage by the lettuce drop or the tobacco wilt is a far more serious matter than a plant disease is usually considered to be. The diseases which develop on the product after harvest, while in storage, are of peculiar destructiveness since they cause the loss of a large percentage of the finished agricul- tural yield. ^' ^ Thus a large part of the total yield of sweet potatoes is lost. Those diseases that develop in transit entail, in addition to the loss of the product, also the freight charges and many hundreds of thousands of dollars in litigation. Some of the losses caused by diseases of a few crops are given below, merely as illustrative instances. The authority is named with each estimate. These losses are in many instances much larger than is indicated, due to increase in market value of the product. The California vine disease in 1892, $10,000,000. Pierce. Wheat rust in the United States, 1898, $67,000,000. Galloway. Wheat rust in Illinois, 1885, $1,875,000. Burrill. Violet leaf-spot in the United States, 1900, $200,000. Dorsett. Peach leaf-curl in the United States, 1900, $2,335,000. Pierce. Potato late-blight in New York, 1904, $10,000,000. Stewart. Oat smut in the United States, annual, $6,500,000. Orton. Wheat loose smut, United States, annual, $3,000,000. Orton. Wheat bunt in the United States, annual, $11, 000,000. Orton. Potato blight in the United States, annual, $36,000,000. Orton. Wheat, 1917, all diseases, 64,440,000 bu. Lyman.« Oats, 1917, all diseases, 153,973,000 bu. Lyman. Corn, 1917, all diseases, 175,344,000 bu. Lyman. Potato, 1917, all diseases, 117,174,000 bu. Lyman. Sweet potato, 1917, all diseases, 41,707,000 bu. Lyman. Cotton, 1917, all diseases, 1,866,000 bales. Lyman. PREVENTION OR CURE OF PLANT DISEASES The burden of the efforts of the plant pathologist must be directed toward methods of prevention, which are here worth far more than their proverbial ratio, since, owing to the comparatively small value of the individ- ual among plants, treatment of a plant already sick is seldom attempted except in the case of plants of ex- ceptional value. Such value very rarely attaches to an- nuals or biennials; hence it is only with perennials, valuable vines, bushes, or trees that cure of the in- dividual is attempted, and here only in a few special cases. The science of plant pathology, barely antedating 1880, is yet young. Several of its founders in America are living and are still vigorous workers. In comparing this youthful science with its far more aged prototypes, human and vet- erinary medicine, one is astonished at the progress already made, rather than abashed at the multitude of diseases as yet unconquered.'^^ Among all classes of crops are diseases, single or many, which have given way to the control of man, many of them diseases of great destructiveness, yet which are now prac- tically under the subjugation of the intelligent, educated crop producer. The remedies, with one or two exceptions, are entirely the result of patient, scholarly investigation, careful de- duction, followed by experimenting, testing, and improving. Such investigation is ever proceeding with increasing ac- tivit}^, and each year, new or improved methods of combat are devised, so that the future may with confidence be relied upon to see the subjugation of many of the foes that are as yet un conquered. 13 14 Diseases of Economic Plants Methods of Prevention All methods of prevention of plant diseases due to par- asites aim at the destruction of the causal organism, the diminution of its numbers, or the strengthening of the crop plant so as to withstand its attack. The various methods employed may, for convenience, be summarized as follows : — 1. Killing the causal organism as it rests upon the seed. — Examples: oat or wheat smut, cabbage black-rot. For this purpose the seeds (sometimes cuttings or even whole plants are similarly treated) are subjected to the action of heat or disinfecting chemicals long enough to kill the causal organism, but not long enough to kill the seeds. Chief among such disinfectants are : — Formalin (40 per cent formaldehyde). Corrosive sublimate. Copper sulfate, followed by weak limewater. Heat. 2. Killing superficial fungi by applications upon the green parts of the plant. — Examples: powdery-mildew upon grape, gooseberry, or rose. This method is applicable only with the purely superficial fungi, since internal para- sites cannot be so reached without injury to the host plant itself. It finds prominent application with the powdery- mildews. The chief applications used are : — Liver of sulfur. Bordeaux mixture. Ammoniacal copper carbonate. Sulfur, or sulfur and lead arsenate. Lime-sulfur. 3. Killing superficial fungi hibernating upon the bark of the dormant plant or plant supports. — Examples: apple hypochnose, peach curl. For this purpose cleansing sprays, often called dormant sprays, may be used. Since the parts of the host receiving the spray are highly resistant to their poisonous action, the sprays thus employed may be much Prevention or Cure of Plant Diseases 15 stronger than could safely be used when the plant is in foliage. For this purpose use : — Copper sulfate with lime sufficient to color. Lime-sulfur mixtures. 4. The use of protective sprays or dusts. — Examples: grape black-rot, apple scab. A protective spray or dust is one applied to the plant upon its bark, foKage, or fruit, to kill any offensive germs that may fall upon its surface, or to pre- vent their growth upon or into the plant. Such sprays are distinguished from the cleansing sprays, which are not primarily for protection against future invasion, but rather for the purpose of cleaning off or killing all spores actually upon the plant. Protective applications are usually em- ployed when the plant is in foliage, and therefore must be used with due regard to the susceptibiHty of the plant to the poison employed. They should be applied : — 1. Often enough to replace any previous protective ap- plications that may have been removed by rain or other means. 2. To give protection to any new surface of twig, leaf, or fruit which has developed since the last protective treat- ment was made. The first protective application should be given as soon as possible after susceptible surfaces have developed, and before the attacking organisms are expected to make their invasion. The time varies of course with each special crop, with each disease, with the climatic relations and section of the country. Nor can any absolute rule be laid down for the use of subsequent protective applications. Fre- quency of rain is an important controlling factorr A fungi- cide, if rained upon just after it is applied and before it has time to dry, is easily washed off. New tissue and new surfaces develop every day; there- fore, theoretically to secure complete protection, sprayings should be very frequent, much more frequent than is prac- ticable. To meet the needs occasioned by new growth, pro- 16 Diseases of Economic Plants tective sprays are usually given at intervals of from ten to fourteen days, though special rules must govern special cases. The chief protective applications are : — Bordeaux mixture, full strength or weak. Ammoniacal copper carbonate. The latter solution possesses the advantage that it does not spot the fruit and may therefore be used near the period of maturity, when the Bordeaux mixture, owing to its spotting effect, would be less desirable. Lime-sulfur mixtures. Sulfur and lead arsenate. 5. Excision of the affected parts. — Examples: Ash white-rot. Excision is resorted to chiefly in the case of trees which from their location or quality possess value suffi- cient to warrant the necessary outlay of labor. It is so practiced as to remove the diseased wood and sufficient of the healthy wood to expose an entirely un contaminated sur- face. The wounded surface is then treated with an antiseptic such as tar or carbolineum. 6. Removal and destruction of diseased twigs, leaves, or fruit. — Examples: fire-blight, peach brown-rot. The removal and destruction of diseased parts diminishes the number of bacteria, spores, etc., that are available to spread the disease and thus lessens infection. Mummified fruit should be picked from the plant or the ground and destroyed, or it may be removed by appropriate pasturage by fowls, swine, etc. Affected leaves in many instances should be similarly removed. Blighted twigs and cankers should be cut out when seen. 7. Removal, in whole or in part, of complementary hosts. — Examples: apple rust, wheat rust. Complementary hosts always serve as multiplying places for the causal parasite, and in some instances are absolutely essential to its hiberna- tion. Such complementary hosts should, when practicable, be removed from the immediate vicinity, and, when possible, not allowed to exist within considerable distance, one eighth Prevention or Cure of Plant Diseases 17 to one half mile, or better still, a greater distance. When it is not practicable to remove the host, the offending por- tions may be cut away, e. g. in the case of the apple rust the cedar-l)alls may be removed from adjacent trees. 8. Avoidance of disease-bearing material or material favoring disease. — Infection may reach hay through sick melon vines (melon wilt), or manure may be contaminated by infected plant parts (potato scab, cal:)bage rot, melon wilt, etc.). Soil may wash from one field to another and bear disease with it (tobacco wilt, melon wilt, etc.). 9. Prevention of wound infection. — Excnnples: heart- rots, sap-rots, cankers, fruit-rots. Wound infection may often be avoided by care in handling the plant so as not to wound it. In trees place ladders carefully, not roughly, among the limbs; avoid walking on limbs with nailed or hard boots, etc. Gather all fruit, root-crops, etc., carefully to avoid breaking the skin or bruising the underlying tissue. In case of removal of large limbs, coat the exposed wood with paint or tar to prevent invasion by parasites. 10. Avoidance of susceptible varieties ; selection of resist- ant varieties. — There is much difference in the suscepti- bility of different varieties of plants. Study the different varieties of the crop to be raised, particularly in this regard, and use those that are most resistant. In case resistant individuals are observed among sick plants, save their seed carefully and test the resistance in succeeding years. In this way new and resistant varieties may be developed. 11. Avoidance of disease-infested localities. — This is in many cases imperative where the soil is invaded by a germ inimical to the growth of crops of certain kinds, as in the case of cabbage black-rot, cotton and melon wilt, etc. Similarly, low damp locations favor diseases of some crops (potato late- blight) , and the proximity of certain kinds of plants leads to disease with others (apple rust). All this should be con- sidered in the selection of land for the crop. 12. The practice of crop rotation. — Constant growth of the same crop in any locality tends to increase the enemies 18 Diseases of Economic Plants of that crop. Rotation breaks the continuity and hinders the multipHcation of the parasite. 13. Avoidance of practices that aid in dissemination of the parasite. — Examples: bean pod-spot, tomato leaf -spot. In certain instances the spore of the causal fungus is trans- ferred from plant to plant most freely when the host is wet. To avoid picking or cultivating under such conditions is to lessen the spread of infection. Similarly in the greenhouse, surface watering may spread the spores. By sub-irrigation this may be avoided. The importance of sanitary methods cannot be over- emphasized and stress on such methods rather than on the employment of specific treatment against disease is a growing tendency. Many crops from their very nature are but slightly amenable to direct treatment; others will not need it if they are given surroundings that are, in general, sanitary. Increased attention should, therefore, be given to soil condi- tion both chemical and physical, to the fitness of the crop to the particular soil and climate, to water relations, to crop rotation, to closeness of planting, ventilation, to proper seed selection, and modes of propagation. GENERAL DISEASES The diseases discussed below are present upon so many different species of plants that it would seem that they are almost indifferent to the nature of their hosts. They may, therefore, be expected upon any kind of plant, and are here mentioned so that it will not be necessary to discuss them repeatedly in succeeding pages. Special reference is also made to them under the hosts upon which they are most destructive. Damping-off. ^^' ^^' ^^ — SeedUngs, cuttings, and other weak, soft plants which lack in the vigor that affords them natural protection against their enemies, are subject to a disease which has come to be generally known to gardeners as '^ damping-off." Damping-off is most injurious to seedlings grown indoors or under crowded conditions, but it some- times occurs in the field. It is particularly injurious to seedling trees in the nursery where many young seedlings die and disappear, or even die before they come above ground. The loss is thus often 90 per cent of the stand. Typically damping-off occurs upon seedlings as a rot originating at or near the surface of the ground. The decay at this point so weakens the stem that the plant topples over or ''damps- off." Subsequently the whole plant may decay, either from the primary cause or from secondary attacks. A short time prior to the fall of the plant the leaves may appear sickly, although this sign is so evanescent that it may not be noted. Upon cuttings the toppling over does not, of course, occur, but the rot at the ground line is of the same nature as in the case of seedlings, and since the diseases in the two cases are of similar nature and due to similar causes, they are placed under the same caption. Damping-off may be caused by any one of several species 19 20 Diseases of Economic Plants of fungi, prominent among them being Pythium, Thielavia, Corticium, Fusarium, Botrytis, Sclerotinia, Sclerotium, Phoma, Volutella, Phytophthora, CoUetotrichum, Gloeospo- FiG. 4. — Stems of young greenhouse tomato plants damped- off frcm attacks of Corticium. After Humbert. rium. The fungus which causes this condition ma}^ often be seen as a weft of myceHum around the base of the diseased plant, or even creeping over the ground to some distance. General Diseases 21 From its original points of attack it may spread rapidly to adjacent plants, often sweeping the whole seed bed. Since the growth of these fungi is favored by moisture and warmth, the trouble may often be checked or pre- vented by keeping the beds cool and withholding any excess of water; also by means of adequate ventilation, preventing the accumulation of a vapor-laden atmosphere around the bases of the plants. Thick sowing should be avoided. Frequent stirring of the top soil around the plants aids in drying it and may stop an incipient attack of damping-off. Organic matter in the soil favors the growth of damping- off fungi, and should be avoided. Fresh, clean sand is best for most purposes of the seed bed and cutting bench. Soil known once to have sustained damping-off may be regarded as infested with the fungus which caused it. Such soils should not be used for seedlings or cuttings without disinfection. If disinfection is impracticable, the soil should be removed, the containers thoroughly cleansed with a spray of Bordeaux, bluestone, or formalin, and new unin- fested soil introduced or, in the case of seed beds, a new site selected. Stem-rot, Root-rot ^^' ^^ {Cortidum vagum B. & C, Rhizoc- tonia). — The affected plants are usually attacked near the soil-line or on the roots where cankers of small or large extent develop. These cankers vary in character and color with the host and conditions so that reliable diagnosis can be made only by recognition of the fungus with a compound micro- scope. There appear very fine, cobwebby threads, pale or dark, which are often barely visible around the roots of the affected plants as they are pulled from the ground. Masses of fungus threads (sclerotia), also often occur. These are black, irregular in shape, the size of a pin-head or larger. Usually the fungus does not bear spores, but in relatively rare instances sporiferous regions develop encircling the stem. This stem-rot has long been known in Europe, and is now found in North and South America, the West Indies, India, 22 Diseases of Economic Plants Fig. 5. — Corticium on cabbage. Peltier. cherry, ble to raspberry, its attack and Australia, and may be regarded as of world- wide distribution. The first account of it in the United States was made by Pammel in 1891. Since then nu- merous bulletins deal- ing with it on various hosts have been pub- lished. It is quite in- different to its hosts, embracing especially members of the pink, crucifer, legume, po- tato, and sunflower families and in all about fifty families of plants including conifers and ferns. Some 165 spe- cies and varieties of host plants are re- corded. Among these, the most important in America are : potato, beet, lettuce, bean, cel- ery, carrot, cabbage, eggplant, tomato, sweet potato, cucum- ber, watermelon, pump- kin, squash, pea, corn, radish, rhubarb, alfalfa, clover, buckwheat, to- bacco, cotton, aster, carnation, violet, currant, pine. If conditions favora- obtain, the fungus may well be ex- After General Diseases 23 pected upon almost any species of plant, so wide is its range of hosts. Soil disinfection (p. 460), when practicable, may be em- ployed; otherwise general sanitary measures, destruction of infective refuse, and the use of resistant plants are remedial. Southern-blight^'^ (Sderotium rolfsii Sacc). — Plants af- fected with this disease lose color, wilt, and may die. The fungus is found, usually, around the base of the stem or on the roots, producing lesions of rot, a dense white mycelial mat, and large numbers of spherical, yellow sclerotia, closely resembling mustard seeds, which are diagnostic. The causal fungus may be recognized upon numerous hosts particularly in the Southern states, and as far north, at least, as central lUinois. It has been identified upon tomato, eggplant, Irish potato, sweet potato, beet, peanut, pepper, cauliflower, bean, cowpea, cabbage, carrot, squash, muskmelon, water- melon, rhubarb, fig, cotton, violet, hydrangea, daphne, chrysanthemum, pinks, bellflower, morning-glory, Japanese fiber-plant, grasses, sugar cane, and several weeds and may be looked for on any plant. Treatment is the same as for stem-rot. Texas root-rot ^^' ^'^ (Ozonium omnivorum Sh.).* — Most destructive to cotton (see p. 346) this disease affects a very wide range of plants in Texas, California, Oklahoma, New Mexico, and Arizona. It has been noted upon nursery stock, apple, mulberry, chinaberry, linden, ash, quince, locust, Prunus, hibiscus, persimmon, elm, lime, maple, beet, peanut, bean and various legumes, flax, cotton, sweet potato, Sida, ragweed, cocklebur, alfalfa, and several other plants. The chief characteristics are a sudden wilting or dying of the diseased plant, or if the main root is not completely diseased merely a slight yellowing and unhealihy appearance. The roots of plants that have recently died are closely invested with a cinnamon-buff felt of hyphse, in which strands are conspicuous. Treatment is as for stem-rot. * Duggar believes the conidial stage to be Phymaioirichum omnivorum (Sh.) Dug.i7 24 Diseases of Economic Plants Root-rot 1^' 1^ {Thielavia basicola (B. & Br.) Zopf.).— The roots of the diseased plants, especially the tips of the rootlets, turn black and decay. Sometimes the stem just above the roots is cracked and deformed and the plant is dwarfed. Damping-off may occur in seed beds. This root- rot was first noted in the United States on tobacco in 1904 and is now known to be widely distributed. It is found pri- marily on members of the legume, potato, and cucurbit families but has been identified on plants of fifteen other families as well, including the violet, composite, crucifer, and mallow families. In all, something over a hundred species of host plants are known to be susceptible, though to largely differing degrees. In the case of tobacco alone the average annual loss is placed at millions of dollars. There appears to be no biologic specialization and the fungus that can affect one crop can pass readily to the others. For treatment, see under Tobacco, page 253. Root-knot, nematode galls.- ^' ^^' ^^ — Root galls, varying from a few millimeters to a centimeter or more in size and superficially resembling the root tubercles of the legumes, are common upon a large variety of crops, causing large field loss in all but the most northern states as well as serious injury in greenhouses everywhere. Plants badly affected are dwarfed and are more susceptible to attacks of fungi than are normal healthy plants. Large indirect loss arises from the fact that nematode-infested soil often prohibits the planting of certain profitable crops. These galls are due to a microscopic eel-worm (nematode) which enters the root from the soil and by irritation of the root causes the gall to develop. Following is a list of the more important highly susceptible plants. A complete list would number over five hundred hosts. Field crops: alfalfa, clover, cotton, cowpea (except Iron, Brabham, and hybrids of Whippoorwill crossed on Iron), field pea, flax, pumpkin, soy bean, sugar beet, sugar cane, sweet potato, tobacco, vetch. Ornamental and drug plants: begonia, cineraria, clematis, coleus, dahlia, hollyhock, ginseng, goldenseal, peony, rose, sweet pea, violet. General Diseases 25 Truck crops: asparagus, bean, carrot, celery, cucumber, eggplant, garden beet, garden pea, Irish potato, lettuce, muskmelon, okra, onion, pepper, salsify, spinach, straw- berry, tomato. Woody plants: almond, catalpa, cherry, European elm, fig. Old World grapevine, mulberry, peach, pecan, Persian walnut, weeping willow. Fig. 6. — Root-knot (nematode) on salsify. Original. In limited areas soil disinfection (p. 460) may be em- ployed. Thorough cultivation and fertilization induces the roots of perennials to extend deeper into the soil, thus reach- ing below the nematode zone, affording at least temporary alleviation. Three years of rotation with non-susceptible crops as corn, timothy, red- top, velvet beans, resistant cowpeas, barley, winter rye, or oats with care to keep down susceptible weeds largely reduces the amount of soil infection. 26 Diseases of Economic Plants Certain varieties of cowpeas (p. 335), tobacco, grapes, figs, and watermelon show resistance. Calcium cyanamide, 1,000 to 5,000 pounds per acre applied several weeks be- fore planting and followed by abundant water, reduces the number of nematodes. Hairy-root, also due to nematodes, is discussed on p. 162. Certain fungi as Penicillium (Soft-rot or Dry-rot) p. 51, Phytophthora omnivorum, Sclerotinia lihertiaiia (Drop, Wilt) p. 196, are so general in their habits as to be found on almost any host. Disease due to Impure Air.'-^* -^ — Plants are sensitive to certain chemical impurities of the air and may either be killed or greatly retarded in growth by them. These impurities are chiefly smoke and gases or solids resulting from industrial operations. The aerial emanations of smelters are of a character peculiar to the processes involved and of a quantity to make their effect apparent to considerable distances. It has been clearly shown that even small quantities of illumi- nating gas or sulfur dioxid are very deleterious in their effect upon plants. So marked are the effects upon vegeta- tion that definite zones of injury may be mapped in the vicinity of large air-pollution centers, the outer zone extending to a distance of from 75 to 100 miles. Illuminating gas es- caping from mains into the air of the soil frequently causes death of trees. There is considerable difference in resistance between different varieties of plants and if the air pollution cannot be abated the more resistant varieties should l)e planted. Soil diseases.-*^ — A group of plant diseases of special de- structiveness comprises those of which the causal organism resides in the soil from year to year ready to infect any susceptible crop planted thereon. Notorious among such are the wilts of the cotton, tobacco, tomato, cucumber, muskmelon, eggplant, cowpea, water- melon, cabbage, flax, sweet potato and potato; the club- root of cabbage and other crucifers; black-rot of similar plants; smut of onion. Other soil diseases are potato wart General Diseases 27 and scabs, beet scab, lettuce drop, and numerous others mentioned on following pages as well as the general diseases discussed al)ove. Since these diseases are similar in their mode of multiplication and dissemination they are given general consideration here. The peculiar destructiveness of these diseases is due to the fact that they not only kill the crop, but they also prohibit successful culture of susceptible crops in succeeding years. This crop limitation, if the crop in question be an important one, perhaps the only really profitable one suited to the soil affected, may result in large depreciation in land values. It is unknown how long the germs can live in the soil without susceptible host plants. That they can live from one season to the second season following is certain. A field slightly affected one year, if put to a susceptible crop the second year after, will be even more seriously infested, and the trouble will grow so long as such crops are cultivated wdth but short intervening periods. Many cases are known where a rest of five and even eight years does not materially restore the soil to normal condition. The application of chemicals to the soil is of value only in rare instances, and even then is questionable. No means of soil disinfection applicable to fields is known. Land once infested, therefore, can become again usable only by eliminat- ing the causal organisms by a long system of rotation which is usually only partially effective, or by the use of resistant varieties of plants, and these in ziiost instances are not as yet known or do not as yet exist. In view of these facts it is especially necessary to stress the importance of protection of soils against infestation. To understand the means of protection the modes of dis- semination must be known. All plants affected with these diseases harbor immense numbers of the reproductive parts of the causal organisms, bacteria, spores, mycelium, sclerotia, etc. Upon the death and disintegration of the host plant they are liberated in I'M' General Diseases 29 the soil, where they are able to live for considerable time, frequently for years. The immensity of their number in a diseased plant is inconceivable. Even a few diseased stems, roots, or leaves in the field will stock the soil thoroughly. In- fected plants, or soil in which infected plants have grown, or which bears parts of infected plants can therefore convey such contagion to new fields. Instances may be cited where the contagion has spread by washing from higher to lower land; moreover contagion may be carried by any means which can convey soil from one field to another, notably through tools which have been used on infested soil. Though apparently clean, such tools, if they bear even minute particles of soil, may convey hundreds of germs and thus start an epidemic in a field. The hoofs of animals or the feet of laborers may in a similar way bear disease-laden soil. Wind passing over an infested field may pick up broken bits of sick plants or germ-laden soil, and convey these to other fields. Infestation by wind, however, seems to be rare, possibly because of the ger- micidal action of the sun's rays upon the surface layer of soil upon which the wind must act. If the crop be one which is used for stock feed or one which may become mixed with stock feed, the organisms may be spread widely through manure which has here become infested from the feed (cf. watermelon, cabbage). A field may be protected from higher land that is in- fested by proper arrangement of dykes. In some cases a thorough cleansing of tools so that there is no possibility of conveying the germs will aid in repression. The dirt may be knocked off, then wiped off, and the implement finally disinfected with a solution of 2 per cent foraialin or 5 per cent carbohc acid. It is difficult to insure complete protec- tion against disease dissemination by the feet of animals and man, but if uninfested land remains to be protected, every precaution should be exercised in this particular. Where but a few plants in a field are affected, they should be removed from the soil and destroyed by fire, — root, 30 Diseases of Economic Plants branch, and leaf. Prompt action here may materially lessen the rapidity of spread of the disease in the field. Every particle of the sick plant burned means the destruc- tion of millions of the causal organisms. A long rotation of crops, one that will bring the suscep- tible plant back upon the affected field only after an inter- vening period of several years, perhaps after a period of eight or ten years, is useful in some cases, notably with tobacco wilt and onion smut, though in other cases, notably watermelon wilt, such rotation is of httle avail. The one means of overcoming these soil diseases, which is most promising to farmers, lies in the discovery of a variety of the crop plant that will not succumb to attack even when planted upon infected soil. Varieties of cotton, tobacco, tomatoes, cabbage, flax, cowpeas, and watermelon that are resistant to their respective soil diseases have been dis- covered or developed by breeding. There is similar hope in regard to other crops. DISEASES OF SPECIAL CROPS POMACEOUS FRUITS 28 The pomaceous fruit plants, owing to the fact that they are long-Hved perennials, that their products are standard and of high value, that they are universally grown throughout the United States, when subject to an injurious disease justify Fig. 8. — Apple bitter-rot in early stages showing acervuli. After Scott. careful consideration of the means of combating the disease and the employment of even expensive methods to attain the end. APPLE Bitter-rot '^^'^^ {Glomerella cingulata (Stonem.) S. & v. S., Gloeosporium) . The effect of the disease is seen upon both the fruit and the twig. Upon the fruit the rotten spot is 31 32 Diseases of Economic Plants at first soft and wet, in later stages corky, more or less dry, and brown, tan-colored, or black. This spot under favorable conditions increases in diameter at a rate varying from 1- 10 mm. each day. Single or numerous lesions may appear upon the fruit, depending upon the abundance of the infect- ing spores and their ability to gain access through the cuticle. When a spot becomes quite large, it is usually somewhat de- pressed, with a shriveled, wrinkled surface, due to loss of turgor of the un- derlying tissue caused by evaporation. As the spot ages minute spore-bear- ing pustules of the causal fungus, barely visible to the naked eye, appear, first at or near the center. The tissue of the fruit is affected to some depth, although the progress of the disease is not so rapid downward as laterally. The pulp of the apple at the margin of the rotten region is usually bitter, thus giving rise to the common name of the disease. Fruit of any age after its formation is liable to infection if suitable climatic conditions and infective material obtain, though the disease is most noticeable and does most damage as the fruit approaches maturity. A series of hot, wet days favors a destructive attack, while cold checks it. The fruit as soon as it is badly rotted usually falls from the tree, covering the ground beneath, while apples less advanced in disease still hang upon the limbs. This same disease occasionally affects twigs and young branches, causing cankers or rough spots in the bark. Young cankers are slightly rough, owing to the dead bark, and ex- FiG. 9. — Apple in advanced stage of bitter-rot. After Scott. Pomaceous Fruits 33 tend only partly around the twigs. Old cankers are very rough, and may extend several centimeters longitudinally along the twig, thus giving it a flattened appearance. ^f •..^ ' '^*'v ^ "^'--^ Fig. 10. — Bitter-rot cankers. After U. S. Dept. Agr. The fungus causing the rot upon the fruit was described in 1856 by Berkeley. That the cankers are caused by the same fungus was recognized independently by two research parties, Burrill and Blair, and von Schrenk and Spaulding 34 Diseases of Economic Plants in 1902. Upon both twigs and fruit the spores are borne in great numbers. The fungus is, moreover, perennial upon the twigs, the cankers serving as initial points of in- fection for each year's epidemic. The natural course of the disease is through twig infec- tion; spores from some older lesion are transferred to points of weakness on the twig, such as bark ruptured from any cause. The fungus may also develop and overwinter in old cankers caused by other fungi, on dead twigs or scars on the fruit spurs, or even in the crevices in the bark and at these points produce spores the following year. These in turn, carried chiefly by rain, partly by insects, possibly birds, or other agencies, fall upon apples, and there initiate spots of rot. Apples thus infected serve as multiplying ground for the further infection of other apples. Six days after an apple is infected a crop of spores may mature and be ready to further spread the disease. To some extent the causal fungus hibernates in mummified fruits, which thus become sources of initial infection in the succeeding year. Bitter-rot occurs throughout the United States wherever apples grow, but has been most destructive heretofore in sections southwest of Virginia between the parallels of 35° and 39° north latitude. It is known also in comparatively harmless form in Europe and Australia. In 1900 it was esti- mated that the loss in four counties of Illinois was $1,500,000. The president of the National Apple Shippers Association estimated the damage to the apple crop of the United States that year as $10,000,000. There is often a loss of from 50 to 75 per cent of the crop. Two modes of treatment are useful : fii'st, to cut off and burn the cankers in so far as is practicable, and to hand-pick and destroy mummified fruit; second, to spray the growing fruit with a fungicide. The trees should be sprayed fre- quently with Bordeaux mixture, or lime-sulfur (summer strength) from the time the petals fall until the fruit is almost ripe. A non-spotting spray should be used for the last application. Cf. p. 447. Pomaceous Fruits 35 Scab ^^' ^''' ^^^ {Venturia inoequalis (Cke.) Wint., Fusicla- diwn). — This is justly called the most injurious disease with which the apple grower has to contend. Originally imported -— r-r^^ Fig. 11. — Bitter-rot cankers in which perithecia were found. After Burrill. from abroad, the first record is in Europe, 1819. Later it was noted in America, both in New York and Pennsylvania, in 1834, whence it apparently spread westward. It affects 36 Diseases of Economic Plants both fruit and leaves, probably in all localities where apples are grown, and is serious in Europe, Australia, Africa, and New Zealand, as well as in America. Upon the fruit, the scab first causes the skin to take on a dark olive-green color; later, as the outer skin breaks and Fig. 12. — Apple scab. After Craig. exposes the fungus underneath, the color changes to black. An apple in this stage is shown in Fig. 12. Still later the scab enlarges, and the spores and fungous cells at the center of the spot may fall away, leaving a skin of rusty appearance surrounded by a dark ring where the fungus has not yet fallen off. Farther from the center of the spot may be an olive-green or silvery ring, showing the still younger stage of the disease. Cracking and distortion occur in cases of very Pomaceous Fruits 37 badly affected fruits. Scabby fruits are much more sus- ceptible to storage rots than are clean fruits (p. 49). Upon the leaves and more rarely upon twigs the fungus forms a thick velvety coat, varying from dark olive-green to black, in spots at first circular in outline, later irregular and coalescing. The irritation and retardation of growth caused by the presence of the fungus often induces the leaves to curl and wrinkle in a characteristic manner. The fungus winters on fallen leaves, and wind-borne spores from them give rise to spring infection. Cf. pp. 58, 60. The injuries by this disease may be enumerated as fol- lows: lessened leaf value, retarded twig and wood growth, premature fall of fruit, retardation of full de- velopment of fruit, and injury to sale and keep- ing quality of fruit. Baldwin, Golden Rus- set, and Hubbardston are among the most re- sistant varieties, though scab-resistance seems to vary geographically and even seasonally. Cf. p. 60. Bordeaux mixture and lime-sulfur are effective sprays. It is especially important to apply the mixture immediately be- fore the blossoms open, again just after the petals fall, fol- lowed by one or two later sprayings. Cf. p. 57. Dusting is discussed on page 446. Burning of infected, fallen leaves is a good sanitary measure. Blotch ^^"^o- ^-1 {Phyllostida solitaria E. & E.). — In some sections of the country this disease of bark, leaf, and fruit is even more troublesome than any of the preceding, though its Fig. 13. — Apple blotch, and Rorer. After Scott 38 Diseases of Economic Plants distinct identity was not recognized until 1895. Since then the disease has been observed in the Eastern and South- eastern states, though not in serious form. Its most destructive center, heretofore, has been in the Ozarks of Arkansas and Missouri and in southern IlUnois, Ohio, and Indiana where a large per cent of the crop is commonly rendered unfit for barreling. One county alone in Arkansas is estimated to have suffered a loss of $950,000 in 1906. Owing to its superficial similarity, blotch has been con- founded with scab in some in- stances. The first publication con- cerning the disease appeared in 1902, and the first detailed de- scription in 1907. Upon fruit the blotches are from 5-20 mm. in diameter, dark in color, with an advancing margin of peculiar, irregular, jagged, or fringed appearance. By coales- cence large spots may form, and owing to tension, cracks appear, enlarging to a centimeter in length, or even girdling the fruit, and reaching to the core. In the older portions of the blotch, minute pycnidia develop. These blotches mar the appearance of the fruit and injure it as a salable product. Upon twigs, spurs, or shoots are produced cankers, which, during the first year, consist of small spots 2-10 mm. in diameter, tan-colored, each bearing several pycnidia. The margins of the spots are sharply limited, and are usually Fig. 14. — Apple blotch on twigs. Original. Pomaceous Fruits 39 bordered with a narrow red line. In older cankers the diseased bark becomes cracked, furrowed, and much rough- ened. On the leaf this fungus causes small, regular, light brown, yellowish, or whitish spots, usually 1-2 mm. in diameter, each of which may bear one or several pycnidia. The Ben Davis, Missouri Pippin, Limber Twig, and Maiden Blush are highly sus- ceptible, while Winesap, Jona- than, and York Imperial are almost immune. Ordinarily three applica- tions of 3-4-50 Bordeaux mixture suffice to control blotch. The first spraying should be made two or three weeks after the petals have fallen; the second about two weeks later; the third two weeks thereafter. Lime-sulfur should be substituted during wet weather to avoid Bor- deaux injury. Careful prun- ing to remove affected twigs is beneficial. Rusts ^^' ^^' ^^^ (Gymnospor- angium sps., Roestelia). — Rusts of the apple may usually be recognized by their char- acteristic spots on the leaf, or more rarely upon the fruit or twig. These spots, yellowish green at first, gradually become darker, approaching orange. Upon close examination, the upper surface of one of these discolored spots is seen to con- tain numerous pustules, at first honey yellow, finally black, Fig. 15. — Apple leaf affected with rust. After Anderson. 40 Diseases of Economic Plants smaller than a pinhole, while upon the lower surface of the diseased spot appear some weeks later the fringe-toothed cluster-cups. This spot is sometimes so abundant that its presence upon orchards may be recognized at great distances by the characteristic hue imparted to the foliage mass as a whole. Rust robs the tree of nourishment and renders normal fruitage impossible. A peculiar relation exists, in that the causal fungus spends part of its life on one plant, the apple, and the remainder upon a totally different plant, the red cedar (Juniperus), the Alternate Host of the apple rust. The fungus summers upon the cultivated apple or the wild crab-apple tree, from which later spores are borne by the wind to adjacent juniper or red cedar trees. There the fungus grows and causes the familiar ''cedar apple." In the spring the. cedar apple produces gelatinous, horn- like projections, each bearing myriads of spores, which, when conveyed by the wind to the susceptible apple tree, under suitable conditions, cause the apple rust. Evidence that this relation really exists is readily found if one ex- amines an orchard having red cedar trees upon its windward boundary. It is clear that the more red cedar trees there are in the neighborhood of an orchard, especially to windward, the more probability there is of damage from the rust. The rational treatment, therefore, is to remove these trees in so far as possible, or if the value of the cedar warrants it to hand-pick the cedar galls. In rare instances spores may be carried several miles, but orchards are reasonably secure if all possibility of infection from the immediate neighborhood be removed; that is to say, for a radius of two miles. In case the red cedars are too numerous, or if for other reasons it is impossible to cut them, spraying the apple trees at a time corresponding with the spore discharge from the cedar-galls will lessen the evil, but the success of spraying is neither complete nor certain. Resistant apple varieties are : Yellow Transparent, Maiden Pomaceous Fruits 41 Blush, Baldwin, Grimes, Stayman, Winesap. The following are more susceptible: Wealthy, Jonathan, Rome, York Imperial, Ben Davis, Greening. Fire-blight^^ (Bacillus amylovorus (Burr.) Trev.). — De- scription and discussion of this disease will be found on Fig. 16. — A cedar apple in condition to give off spores. After Anderson. page 62 under pear, the blight of which is identical with the apple disease. Its character and treatment are the same upon both hosts. While the bhght is preeminently a pear disease, it also affects the apple very seriously, particularly in the form of blossom-blight and body-blight. 42 Diseases of Economic Plants The Lowell, Isham, Smith Cider, Yellow Transparent, Jonathan, and Willow Twig are especially susceptible varieties, while Celestia, Buckingham, Mammoth Black Twig, White Winter Pearmain, Winesap, and Ben Davis are resistant, the last almost en- tirely so. In general the crab vari- eties are more susceptible than others. Black-rot, canker ^4. 45 (Physalo- spora cydo7ii(B Arn., Sphceropsis) . — In many respects this disease closely resembles the bitter-rot, particu- larly in that it appears both as rot of the fruit and as cankers upon the limbs. In some instances it also appears as a twig blight and as a leaf spot. As seen under the hand lens the coils of exuding spores are black, instead of pink, as is the case with bitter-rot. A compound microscop-'^ is necessary to bring out other distinguishing characters. The limb cankers, first studied by Paddock, consist of swellings, with the bark rough, and black. In other cases the black, decayed wood from which the bark has dis- appeared is exposed. This cankerous infection sometimes ex- tends for nearly a meter along the branch, and occasionally girdles it. When occurring upon the trunk or main branches it is called black-rot body-blight. The Tolman Sweet is said to be quite resistant to canker, while Twenty Ounce is very susceptible. Four other va- rieties range in susceptibility as follows: Baldwin, Wagener, Greening, King. Black-rot twig-blight somewhat resembles fire-blight with Fig. 17. — Apple black-rot canker showing numer- ous pycnidia. After Whetzel. Pomaceous Fruits 43 which it is often associated, but may be distinguished from it by the presence of myriads of minute pimples distributed thickly over the affected region. With a hand lens coils of spores may often be clearly seen issuing from these pustules. Upon the leaf, blighted spots are produced, irregularly circular in outline, often marked by concentric rings. The body of the spot is brownish and the margin sharply limited. Similar spots are caused in several other dis- eases, and definite knowledge of the nature of leaf spots must depend upon microscopic diagno- sis in each special case. The various forms of this disease which have been noted above are found in Nebraska, Michi- gan, the Ozarks, Ohio, Wisconsin, and throughout the Allegheny and eastern apple sections, and are troublesome each year. The treatment should be the same as that recommended for bitter-rot with special care to avoid bark wounds of all kinds, as from ladders and workmen's boots. A rot upon fruit very similar to bitter-rot, and a twig- FiG. 18. — Pacific coast canker. After Cordley. 44 Diseases of Economic Plants blight very similar to that of black-rot, though less important, is caused by Coniothyrium fuckelii Sacc.^*' Pacific coast canker ^^' ^^ (Neofabroea malicorticis (Cord.) Jack., Gloeosporium) . — The Pacific coast canker, first noted about 1893, is particularly destructive in the Northwestern states and British Columbia west of the Cascade Mountains. The bark or sapwood of twigs and larger branches is the seat of infection, but the disease may occur also upon the fruit when in storage. The loss of an entire orchard within a few years has resulted. Young trees, owing to their tender bark, are especially susceptible. Upon twigs, cankers in the early stage appear as round or oval, slightly sunken, dark areas which increase but slowly in diameter. As soon, however, as the fungus penetrates into the cambium and sapwood the canker enlarges very rapidly, making its most rapid development through the cambium, and advancing more tardily through the overlying bark. The resulting spots are nearly circular, quite black, and from 5 mm. to 12-14 cm. in diameter. When old, the bark becomes brittle and a definite fissure separates the dead from the healthy portions, indicating cessation of advance of the fungus. The diseased bark eventually falls away, leaving a scar. Branches, or even trees, may be killed by girdling cankers. Upon stored fruit the disease appears first as light-brown, circular, rotten spots. These later turn very dark or black, and become depressed, dry, and tough. Acervuli similar to those upon the bark soon develop in concentric circles. When the cankers are few, on small trees, excision may be practiced to advantage; when, however, there are hun- dreds of cankers upon each tree, this treatment is manifestly impracticable. Spraying with strong Bordeaux mixture in the fall, after the crop is gathered and again after an interval of about three weeks, is valuable to prevent the formation of new cankers, and has established practical control of the disease. Blister-canker "^^"^^ {Nummularia discreta (Schw.) Tub). — • Attention in America was first called to this active, parasitic Pomaceous Fruits 45 disease in 1902 by Hasselbring, who attributed to it more serious results than from any other canker disease of IlHnois. In many cases large limbs and even whole trees are killed. It has been reported in many states, including Arkansas, Okla- homa, Nebraska, New Hampshire, New York, and Virginia. The cankers are at first in- conspicuous, unhealthy, dirty brown, usually depressed spots in the bark, sometimes 15 cm. in diameter, which enlarge rapidly, particularly lengthwise upon the limb, a crack often marking the boundary between dead and sound bark. The interior of the bark of such spots is mottled with dead regions. In autumn the sporiferous bodies appear near the bor- ders of the diseased spots, first pushing through cracks in the bark, and exposing pale grayish ochre-colored fungous growths 3-6 mm. in diam- eter,which, when mature, are slightly saucer-shaped, and dark in color. These bodies are attached to the dead wood, and remain there even after the bark has fallen away, thus constituting a diagnostic character of absolute reliability, separating this from all other cankers. Discoloration of the heartwood often occurs at a distance of a meter or more from the ap- parent seat of disease. When the cankers become large, injury to the distal parts through interruption of the water supply results. The Fig. 19. — Black-spot on fruit. After Lawrence. 46 Diseases of Economic Plants leaves show symptoms of disease, and the fruit fails to grow to full size. With complete girdling the limb dies. Since all infection seems to occur through wounds, pre- vention must look largely toward the avoidance of wounds Fig. 20. — Blister-canker. Some of the discs have been re- moved to show the underlying marking. by tools, machinery, harnesses, pickers' ladders, boots, etc. It is also an excellent sanitary measure to cut out and burn all infective material, and in incipient cases excision of diseased tissue in a limb may be practiced with profit. Pomaceous Fruits 47 Leaf-spots ^^"^^ (various fungi) (see also black-rot, p. 42). — Aside from the leaf diseases of apple already mentioned, there are numerous other leaf-spots due to various causes. These spots partake of the same general character. That is, they are brown to tan-col- ored, at first circular, later irregularly circular, defi- nitely bordered, and usually concentrically marked. If abundant, or if they enlarge rapidly upon the leaves, they cause their premature fall, and largely defoliate ; the tree. Such spots pre- vail to greater or less ex- tent in all apple orchards but are most destructive in the Southern states. Numerous species of fungi have been isolated from these spots; some of them undoubtedly sustain a causal relation to the dis- ease. Sheldon claims that in West Virginia much of the apple leaf-spot is due to an Illosporium. Whatever the actual ijausal fungi may be, these spots are all, or nearly all, of fungous origin and are amenable to preventive spraying. The first of three or four applications should be given with the opening of the leaf buds. Rypochnose ^^^ ^'^ {Corticium stevensii (Noack) Burt). — Superficially this disease resembles the bhght, with which it is likely to be confounded by the casual observer. It may Fig. 21. — Apple leaf-spot in late stage of development, showing concentric rings. Original. 48 Diseases of Economic Plants readily be distinguished, however, by two characters: first, the manner in which the leaves droop and mat together, which is quite different from the habit of the blight, the leaves of which neither droop nor become matted; second, by the presence of small sclerotia, white when young, cinnamon-brown when mature, upon the twigs adjacent to the affected leaves. These sclerotia usually meas- ure about 2-3 mm. in diameter. Together with the sclerotia and extending along the twig longitudinally are also found silvery, glis- tening, thread-like, fun- gous growths. This fungus hiber- nates in the sclerotia on or near the terminal bud and thence invades the new twigs as they develop, reaching out upon each leaf, spread- ing over its under sur- face in almost invisible thinness, and causing it to droop, die, and eventually to fall away. Thus, in early autumn, such trees are nearly or quite defoliated. The fruit may also be invaded by the fungus. Hypochnose, first described from Brazil, is known from Maine to Florida and Texas. It seems to be especially de- i^ IG. 22. — Hypochnose, showing mat- ting of leaves. Original. Pomaceous Fruits 49 structive in regions of exces- sive humidity, particularly in the deep mountain valleys of the Appalachians, where whole orchards are some- times seriously affected. Owing to the entirely su- perficial nature of the fungus which causes the disease, and its habit of hibernating upon the twigs, the trees should be sprayed with a strong cleansing mixture, Bordeaux or bluestone, be- fore the buds open, and again just before the blos- soms open. Pink-rot ^^ (Cephalothe- cium roseum Cda.). — This rot is known in many states. It follows apple or quince scab and may be recognized by the white, mildew-like growth which appears in conjunction with the scab which it soon after entirely overgrows and turns to a pink color. While the decay is really caused by Cephalothecium, a rupture made in the skin by the scab fungus is the usual place of entrance. The decayed spot is shallow and slow-growing as compared with other rots. It is ac- companied by a bitter taste Fig. 23. — Hypochnose, showing sclerotia on twig at left and rhi- zomorphic strands on twig at right. Original. 50 Diseases of Economic Plants which is so pronounced as to injure cider made from affected apples. The chief destruction follows the harvest, though the disease is sometimes found in fruit still upon the tree. The Rhode Island Greening, Fall Pippin, Fameuse, Maiden Blush, Tompkins King, and Twenty Ounce are especially susceptible. Chief attention should be directed to the prevention of Fig. 24. — Pink-rot following scab. Anderson. After scab. In storage a dry house, well ventilated, kept at 0° C. (32° F.) gives best rot resistance. Another form of pink-rot due to a species of Hypochnus has been described by Eustace ^^ especially upon Baldwins and Rhode Island Greenings. There is no large surface growth of the fungus on the diseased spot, but the rot often extends to the core. Powdery-mildew ^^' ^^ {Podosphceral eucotricha (E. & E.) Salm., Oidium). — The general appearance of this mildew is similar to grape mildew; that is, the surfaces of the leaves Pomaceous Fruits 51 are more or less covered with a white or grayish fungous growth, in the later stages of which are found numerous very- small black fruiting bodies approximately 0.25 mm. in diameter. This fungus, while of comparatively little sig- nificance to old apple trees, causes much injury to nursery stock, often becoming so serious as to prevent successful budding. Mildew has been reported as especially serious in California and other states west of the Rocky Mountains, and is of some importance in all apple regions. In the Pajaro Valley the fungous mycelium has been shown to hibernate in the buds, resulting in early spring infection of shoots. Another species of mildew, P. oxyacanthce (DC.) De Bary, shows the same general characters as the mildew described above, but is of less economic importance. Three or four lime-sulfur sprayings at intervals of about two weeks, beginning when the buds commence to open, have given best results. Crown-gall. See peach. Soft-rot, blue-mold, rot {Penicillium expansum Lk.) . — Per- haps the most common apple rot is found upon stored apples late in the year. The light, tan-colored rotted area is soft and watery. The decay results in the complete loss of the affected fruit, and, by contagion, in loss to the fruit mass. Upon cracks in the decayed surface, and eventually over the whole rotten part, appear tufts of very short delicate fungous threads, at first white, soon bluish-green, very like the common blue-mold so familiar to the housewife upon canned fruit, the seal of which has permitted air to enter. This blue substance upon the rotten apple consists of myriads of the spores of the causal fungus. This fungus is compara- tively unaggressive and cannot force its way into perfectly healthy tissue; a bruise or rupture of the skin is necessary to its invasion. The best preventive is care to avoid bruising. Root-rot ^^ (various fungi). — Death of trees, without apparent reason from evidence above ground, is frequently due to disease and decay of the roots. While the earlier symptoms may vary, in general they include an abnormally 52 Diseases of Economic Plants large set of small fruits, and in the following season few flowers, deficient growth, and small leaf development and perhaps chlorosis. In cases where only a few roots are diseased the evident effects may be limited to the correspond- FiG. 25. — Clitocybe upon apple. After Wilcox. ing side of the tree. Several years may elapse between the ap- pearance of the first symptoms and final death. The roots, one or all, of trees well advanced in disease show decay, de- pendent in character upon the causal fungus. Several dif- ferent fungi cause root-rot (see p. 370). Among those most common on fruit trees are: Clitocybe parasitica Wil. A Pomaceous Fruits 53 gummy exudate is usually present around the base of the tree and black rhizomorphs adhere to the roots. In late stages clusters of the gill-bearing sporophores (Fig. 25) develop; Ar77iillaria mellea Vahl. Quantities of black, stringy, hard, shiny strands 1 to 2 mm. in diameter occur around the roots and in the adjacent soil. The gilled sporophores appear later (p. 370); Fomes annosus (Fr.) Cke. The sporophores are pore-bearing (p. 371); Septohasidium sps. with smooth pore-bearing surfaces; Ozo7iium om- nivormn Sh. See Texas root-rot (p. 23); Xyl- aria sps.^^ The affected roots are covered with a thin, compact growth of mycelium, white at first, later developing into a black incrusta- tion. Minute, thread- like rhizomorphs ra- diate several centime- ters along the root. Affected roots are soon girdled and the distal parts die. Root-rot, due to one or another of these causes, is of wide and common occurrence, and results in large loss. It is found more frequently on newly cleared land than elsewhere. When the disease has advanced far enough to be recognized, no cure is available, and it is unsafe to replant in the infested place. Wood bearing root-rot fungi should be burned to lessen infection. Wood-rot ^'' of orchard trees is of the general character dis- cussed under Decay in live trees on page 354. It is a very important source of loss on fruit trees of all kinds, about one-half of all bearing trees being infected. The rot may chiefly be avoided by preventing wounds or by treating them with disinfectants. See p. 378. Fig. 26. - lation. ters A. - Brown-rot produced by inocu- Note the fungus forms the let- M. G. Original. 54 Diseases of Economic Plants Frost Injury. ^^ — Varieties of apples differ from each other in their susceptibihty to injury from cold. The injury may be local, on single twigs, or spots on twigs, body, or branch; or general, affecting the whole tree. The damage may be apparent externally or show at first only in a discolored cambium. '^ Sun scald," in which the frosted bark occurs as a cankered area and either peels off, or clings tightly and is sunken, is a frost injury. Twigs may be killed outright, especially if the wood has not ripened properly. Late spring frosts injure, as is well known, the buds, blossoms, etc. Frost cankers may form the threshold for the entrance of various fungi and thus pave the way to disease, e. g. black- rot or bitter-rot cankers. A cover crop tends to lessen frost injury, by diminishing excess moisture in the fall, while avoidance of cultivation late in the season hastens maturing of the wood. Bitter-Pit ^^ consists of a pitting of the fruits with slightly sunken circular spots varying from mere dots to 5 mm. in diameter, which finally become brown. The tissue at the bottom of the pit is dead, brown, and spongy. Similar lesions may occur deep within the tissue of the apple. No parasite is present and the trouble seems to be due to improper water relations. The disease causes considerable loss over a large range of territory. Thinning the fruit to a proper set lessens the damage. Pitted fruit should either be consumed at once or stored or shipped under low-temperature conditions (30°-32° F.,— 1°-0° C.) Jonathan-Spot^^' ^^^ occurs on several varieties of apples including the Jonathan, Esopus, Wealthy, Ortley, and Wolf River. The spots are circular, 2-15 mm. in diameter, abruptly but sKghtly depressed, light brown in color, and are more superficial than those of bitter-pit. The disease may appear on fruit still on the tree or may develop during storage or transit. The cause is unknown. Fruits of variety tending to spot should be consumed early or placed in cold storage. Scald ^^^ is a storage trouble particularly serious on im- Pomaceous Fruits 55 mature apples. It is due to gases given off from apples and may be avoided by aeration. Minor diseases. European canker -^^ {Nectria galligena Bres.). — The Euro- pean canker was not recorded upon the apple in America prior to 1899, when Paddock mentioned its presence in Nova Scotia and New York. Later it was noted in New Hampshire and Ohio and is now known to be widely distributed from the Atlantic to the Pacific. It constitutes a serious disease in Europe and may become of importance here. The canker enlarges year after year, but more slowly than black-rot canker, and displays, when fruiting, numerous minute, deep red perithecia which serve to distinguish it from other cankers. Brown-rot ^° {Sclerotinia cinerea, Monilia) . — One of the most serious apple rots in Europe, this disease fortunately is not as yet destructive in America, though Sclerotinia cinerea is occasionally met with as one of the minor causes of apple losses. It has been observed in several states, notably New York, Missouri, Nebraska, the Virginias, North Carolina, Illinois, Minnesota, Arkansas, and New Mexico frequently enough to call for printed mention. Brown-rot produces complete decay of the affected apples, which turn brown, or later black, become soft and wrinkled, and soon show pustules of bushy mycelium breaking through rifts and fissures in the skin over the diseased tissue. The diseased fruits may mummify upon the tree or more frequently fall to the ground and there shrivel to dry, hard, wrinkled masses, in which the rot fungus winters. Sooty-blotch^^- (Glceodes pomigena (Schw.) Colby). — Irregular, sooty, black blotches, especially conspicuous on the lighter colored varieties of apples, are frequently seen upon unsprayed fruit. The individual blotches measure from 0.5-2 cm. across and are often so abundant that they coalesce, giving the fruit a dirty appearance. The fungus attacks the fruit late in the season, and is strictly superficial. 56 Diseases of Economic Plants It may easily be rubbed off with a cloth. The loss in ready salability, due to the unsightliness of the fruit, is reason enough for protective sprayings. Bordeaux mixture applied at intervals of about two weeks from the middle of June until the middle of August is effective. Fly-speck. ^^" — Growing upon the surface of the fruit and forming numerous clustered black specks closely resembling Fig. 27. — Fly- speck (at left); Sooty-blotch (at right). After Colby. fly-specks, this fungus causes disfigurement of the apple. The generic position of the fungus is in doubt, though it was originally named Lahrella pomi by Montague. Volutella rot^^ (Volutella frudi S. & H.). — In general appearance the volutella rot is not readily distinguished from black-rot, though the texture of the rotted tissue is much firmer and drier. Under the hand lens the sporiferous pustules are seen to be clothed with numerous hairs, which character sufficiently marks it as a separate disease. It has been reported from North Carolina, New York, Wisconsin, and is probably of general distribution. Scurf, an affection of the bark of twigs, is due to Phyllo- sticta prunicola (Opiz.) Sacc; Bark-canker '^ due to Myxospo- Pomaceous Fruits 57 rium corticolum Edg. is superficial on both apples and pears and of little importance; the Fruit-spot, ^^' "^^ (Phoma pomi Pass.), occurs in the northeastern United States, the spots are small, sunken, brown or black; Rough-bark^- is caused by Phomopsis mali Rob. The Septobasidium canker is due to Septobasidium pedicillatu7n (Schw.) Pat. Phytophthora cadorum (L. & C.) Schr. causes a fruit rot. Black-mold, due to Fumago vagans, is superficial, while black-mold due to Alternaria sps. produces a core rot. Plenodomus can- ker ^^° (Plenodomus fusco-maculans (Sacc.) Coons) kills the cortex, which eventually flakes off in long strips leaving the wood bare. Die-back canker ^^^ (see peach) is occa- sionally present, also Fruit rots due to Endomyces and Rhizopus. Rosette, which resembles peach rosette, has been noted in three states. Conditions Infi I— t O IB H o -t-3 o fcC o o o O 00 CO M Vegetable and Field Crops 255 crop, the advent of this disease has caused great depreciation in farm values. Fig. 139. — Tobacco plant in early stage of the GranvUle- wUt. Original. The wilt is now known in North Carolina, Florida, Georgia, possibly Connecticut, and what appears to be the same disease has been described in Cuba, Porto Rico, France, the Dutch East Indies, and Japan. 256 Diseases of Economic Plants The first indication of the disease is given through the leaves, which droop, becoming soft and flabby as though suffering from want of water, the leaves remaining green. A typical case is shown in Fig. 139. Frequently the leaves on one side of the plant succumb earlier than those on the other side, and even a single leaf may show one-sided infection. The wilted leaves dry up, and eventually leaves and stalk die, though the stalk re- mains standing with its dead leaves still clinging to it. At the stage of earl- iest wilting a section across the stem shows a yellowish discolora- tion of the woody por- tion. In more ad- vanced stages, or in sections taken lower on the stem, the wood is found to be pene- trated longitudinally by black streaks. When all the leaves are wilted, the wood and bark at the base of the plant are blackened and the pith decayed, leaving the stem hollow or filled with a soft, rotten residue. If a badly diseased plant is cut off near the ground, a dirty, yellowish, viscous exu- date issues from the cut wood. The root is the seat of the original infection, and any plant which shows symptoms in its foliage possesses roots already in a pronounced stage of decay. In early stages Fig. 140. — Tobacco plant in late stages of the Granville-wilt. Original. Vegetable and Field Crops 257 one root or more may be diseased; in later stages all succumb. In a series of rotation tests, planned and inaugurated by the author,^^^ it was found that growing corn, wheat, cow- peas, clover, and mixed grasses, either singly or in rotation for a period of five years on badly diseased soil, reduced the loss from wilt to an almost negligible quantity. The means by which this disease spreads from field to field, and methods to prevent such spreading, are adequately discussed under soil diseases, p. 26. A similar wilt, but due to a Fusarium, has been reported from Maryland. Wildfire ^^^^ ^'^ (Pseudomonas tabacum (W. & F.)). — A bacterial leaf-spot, first noticed in 1917, is widespread in North Carolina, Virginia, and occurs also in Wiscon- sin. Loss of $100 per acre for entire crops is commonly reported. The spot is 2-3 cm. in diameter, often concen- trically marked, and has a translucent border surrounded b}^ a chlorotic halo. Another bacterial leaf-spot known as An- gular leaf-spot (Ps. angulatum (F. & M.)) was also described in 1917 as destructive in Virginia. The spots are angular and are not surrounded by the halo common in ''wildfire." Leaf-spot '^^^ (Cercospora nicotiance E. & E.). — This dis- ease, most abundant upon the lower leaves, appears as brown, circular spots from the size of a pinhead to a centimeter or more in diameter. Older spots bear white centers bordered by a darker, raised line, and the centers often fall away, leaving ir- regular holes. The whole leaf yellows and ripens prematurely. The disease was first described by Sturgis from specimens sent from South Carolina, where it was destructive, prac- tically ruining the crop. A damage of $1000 to one crop alone was noted. The use of Bordeaux mixture early in the season is permissible and advantageous. Bed-rot {Corticium vagum) . — Damping-off and rot of seedlings occur in the seed bed. The causal fungus may often be seen as spots of web-like white mold upon the ground around the affected plants. The general characters and 258 Diseases of Economic Plants prophylaxis are discussed under damping-off, p. 19. Seed beds known to be diseased should be avoided unless previously disinfected. Drop ^^^ (Sclerotinia liber- tiana) . — Damping-off due to Sclerotinia is reported as a common trouble in seed beds. The injury to the plant is similar to that of the usual damping-off while the fungus presents the charac- ters described under lettuce- drop. Young plants are killed ; older plants may sur- vive, and if set in the field, develop poorly. Mosaic. ^^^' ^^^ — Wher- ever tobacco is grown the mosaic is very widely dis- tributed and destructive. Depreciation of $50,000 in quality was attributed to it in Ohio in 1905. It pro- duces a mottled appearance of the leaves due to varia- tion in texture and green- ness ; parts of the leaf show- ing full green and normal thickness, other spots pale or yellowish green, and thin. Accompanying these signs are distortions due to un- equal growth, wrinkled or curled leaves, and leaves of one-sided growth. Slightly affected leaves are depreciated in value; badly diseased leaves are worthless. Fig. 141. — Tobacco leaf showing leaf-spot. After Conn. Agr. Exp. Sta. Vegetable and Field Crops 259 The cause of mosaic is unknowr), but it has been repeatedly shown experimentally that it can be communicated from plant to plant by first touching a diseased plant and later touching a healthy^ one. The disease then appears within six to fourteen days. Thus the disease is spread largely by topping. In nature it is probably spread by insects. The virus appears to be present in all parts of an affected plant, even in the trichomes, and, when inoculated locally, spreads rapidly throughout the plant, though the disease is not transmitted to the offspring through seed from diseased capsules. Tomatoes, petunia, physalis, datura, solanum (but not the potato), and pepper are susceptible to inocula- tion from tobacco plants. The seed bed should be either new or thoroughly disin- fected by steam or firing, and no tobacco refuse or tobacco water used on it. Diseased seedlings in the bed, if any ap- pear, should be destroyed. It is well to top, worm, and sucker the healthy and sick plants separately, on different days, thoroughly washing the hands with soap and water before passing from the diseased to healthy plants. Orobanche. — This is a true flowering plant, which draws its nourishment from the roots of the tobacco plant to which it is attached. The orobanche occurs in small clusters, its stalks are from 1-4 dm. tall, and entirely devoid of green color. They should be pulled and burned before they produce seed. Root-knot (nematodes), see p. 24. Curing-house '* diseases." — When tobacco is cured by natural heat, various rots may occur. Among these are: Stem-rot, due to various fungi; Pole-rot, consisting of small, blackened areas upon the leaf, limited at first to the regions near the veins. These spots may enlarge within two days to cover whole leaves, and the contents of the entire barn may become worthless, the leaf having become so wet and soft as to readily fall apart. The cause of these rots is not cer- tainly known; indeed there may be several separate or- ganisms, each capable of inducing such rot. 260 Diseases of Economic Plants These troubles can largely be controlled by proper regula- tion of the moisture and temperature conditions, i. e., by building such barns that outside air, when too damp, can be excluded, and yet with proper provision for ventilation to carry off the moisture from the drying tobacco. Wet-butts is due to freezing before curing is complete; White-vein to rapid drying; Black-rot (Sterigmatocystis nigra v. Tieg.) occurs during the sweating, the tobacco turn- ing black and losing its proper texture. It is brought about by too high moisture content. TOMATO. 314, 341 Bacterial Wilt, blight (Pseudomonas solanacearum (EFS.) ). — This disease of the tomato is widespread, especially in the South, and prohibits tomato culture upon many thousands of acres of land. It occurs especially in the states south of Maryland, and has also been noted in New Jersey, Delaware, Ohio, and Colorado. The leaves wilt, either singly or throughout the entire plant at once; growth stops and the plant dies. The stem appears at first dirty green, then brown, then black. It soon shrivels, and the veins become brown and show as narrow black lines, or in section as black dots. The wilting of the foliage and the blackening of the vascular bundles are dis- tinctively characteristic. Soil bearing diseased plants one season remains infested during succeeding years and must be abandoned for tomato culture. The disease is spread from plant to plant largely by the potato bug (Colorado beetle) and other insects. For this reason all leaf-infecting insects should be given special attention. In other respects this disease in symp- toms, cause, dissemination, and treatment is similar to the usual soil diseases. Another wilt, similar but of slower development, is de- scribed as caused by Bacterium michiganense EFS.^.^^ Wilt ^^^ (Fusarium lycopersici Sacc. and Fusarium sps). — This wilt is also widespread. It occurs not infrequently Vegetable and Field Crops 261 as the cause of partial or even total losses of the crop. The plants usually reach considerable size, blossom, and set fruit before showing the disease, which first appears in the field on single plants, generally sickly looking, and of unhealthy color, followed by symptoms of wilt. In the worst cases all of the plants die before the end of the growing season, sometimes quite suddenly at the last; or the crop may mature with plants missing more or less extensively. If a badly affected or dead plant be pulled up, the roots are Fig. 1 i2. — Tomato iiekl sliowiag effect of wilt. found to be decayed. If a plant is pulled up as soon as it begins to show wilting, the roots look healthy and sound, but close inspection shows that many of the larger laterals are decayed at the ends. The disease consists of a dry rot of the roots, commencing at the ends and working upward. The first symptom is a pale yellowish color of the lower leaves, which soon dry from the tip toward the base without spotting. The veins and woody portion of the stem are darkened, especially upon the side bearing the diseased leaves. As to means of dissemination and control, what is said under soil diseases will applj^ 262 Diseases of Economic Plants Leaf -mold {Cladosporium fulvum Cke.). — Under glass in the North and occasionally in the open, especially in the South, this disease is destructive. It occurs as rusty or cinnamon brown blotches on the lower side of the leaf, which turns yellow above, then brown or black, curls, and dies. The loss of food supply consumed by the parasite, together with the loss through destruction of the leaf green, injures the yield seriously. Indoors ventilation is the best remedy, coupled with clean culture to avoid carrying the pest over to another year. On fields Bordeaux mixture would doubtless serve well. The causal fungus of this disease was first de- scribed in 1883 by Cooke from specimens collected in North Carolina. Leaf-spot ^^^ (Septoria ly coper sici Speg.). — A very common leaf-spot has almost precisely the general appearance illus- trated in Fig. 143, except that small pycnidia occupy the spots. It is known through- out the United States, South America, Europe, and Australia, and often causes large loss. In some states it is the most important tomato disease. The total loss in the United States is estimated as $5,000,000 annually. The disease attacks the older leaves first and proceeds toward the top of the plant, often causing the loss of so Fig. 143. — Tomato leaf showing spots of mold. Vegetable and Field Crops 263 many leaves as to give the plant the appearance of blight, and resulting in complete ruin of the crop. The presence of the leaf-spot distinguishes this from any of the blights. Spraying with Bordeaux mixture is effective against this disease though valueless against the various wilts. Especial attention should be given to guard, by spraying, the seedlings in the seed bed, using a wea^k Bordeaux mixture. Moving among the plants when they are wet spreads infection. All refuse should be burned or plowed under. Downy-mildew, late-blight ^^^ (Phytophthora infestans (Mont.) De Bary). — Arising from the same cause as the dreaded potato blight, of which host the tomato is close kin, is the tomato blight which causes large loss of the crop in some sections of California. It has been reported also in Massachusetts and Colorado. As with the potato, the amount of damage is closely dependent upon weather conditions, the disease being greatly favored by a warm, humid atmosphere. It appears suddenly as dark, discolored spots on the fruit and other green parts. On the fruit the spot, usually upon the upper side, is watery and large. Many tomatoes, apparently healthy when picked, rot in shipment, the rot being accompanied, under humid conditions, by a fine, white surface mold. Dark spots upon stems and branches soon extend throughout the whole plant, giving it the appearance of one stricken by frost. Protective spraying with 5-5-50 Bordeaux mixture, as recommended for the potato, will probably serve in case of this disease. In regions of infrequent rainfall it is neces- sary to spray only after each rain. Fruit-rot ^^^ {Phoma destructiva Plow.). — Leaf-spots are present, but it is as a spot upon either green or ripe fruit that greatest injury is incurred. The spots are 1-3 cm. in diam- eter, brownish-black, and depressed. This trouble is most prevalent on tomatoes, originating in the South, and shipped to northern markets, and on such fruits causes heavy losses. Blossom-end rot. — Readily recognized from its name, this troublesome disease is essentially a dry, black rot ap- 264 Diseases of Economic Plants pearing on the blossom end and injurious chiefly to early tomatoes. It is especially harmful, owing to the high value of the early fruit that it destroys. Various factors have been named as the cause, and it cannot yet be said with certainty which is responsible. The trouble is more serious upon droughty soils and can to some extent be controlled by irrigation or moisture con- servation, i. e., increasing the water-holding power of the soils by the addition of organic matter and surface tillage. Early-blight (Alternaria solani (E. & M.) J. & G.). — Ruin is brought to the crop in many seasons, particularly in the southernmost states, by this blight, which is identical with the potato early-blight. The leaves bear numerous, small, usually angular spots, often concentrically marked, which appear first as minute brown specks, later showing a pale center with a darker border. In badly affected leaves the tips dry and curl up. Petioles and stems are also attacked. Thorough spraying with the usual Bordeaux mixture should be begun at the first indication of the disease and continued weekly, or semiweekly if growth is rapid and the weather damp. Often it is still better to begin spraying in the seed bed. Southern-blight (Sclerotium rolfsii Sacc). — This blight IS often completely destructive to the tomato in the south- ernmost states. The first sign is wilting of the terminal por- tion of the plant, distinguishing Southern-blight from other wilts, which commence with the lower leaves. For discussion and treatment, see pepper. Leak {Rhizopus nigricans) . — The effect is much as on strawberries and the loss during shipment is large. Minor diseases Anthracnose (Colletotrichum phomoides (Sacc.) Chest.). — This is chiefly a disease of the ripe fruit, either upon the vines or after harvest. It appears as sunken, discolored spots with wrinkled surfaces and black specks, the acervuli. The disease does much damage to fruit before it is picked, and also in- jures the keeping quality. Vegetable and Field Crops 265 Sooty-mold {Fumago vagans Pers.). — Dense, olive-black growths of mold form upon the leaves. Damping-off occurs in the seed bed. Timber-rot (Sclerotinia), see lettuce. Buckeye-rot (Phytophthora terrestria) is a zonate, hard rot of fruit. Winter-blight. — Loss of S2,500 in one house is re- ported, but the disease is not generally distributed. Develop- ment is dwarfed, and the stems show brown lesions in cortex and bundles, but no parasite has been demonstrated, Ro- "sette ^^^ {Corticium vagum). — This is identical with the potato black-scurf, showing similar lesions upon the root and stem near the ground. The tops have long inter- nodes and dwarfed leaves which are somewhat curled. Upon the ripe fruits, espe- cially those touching the ground, this disease occurs as a brown rot upon a slightly wrinkled epidermis. Hollow-stem appears to be due to improper growth con- ditions. Blossom-drop is due to unknown cause. Leaf-roll is similar to that of potato. Root-knot (nematodes) is common. (Edema.^^^ — This is a condition of overgrowth of certain cells of the plant, causing swelling of veins and leaf tissues, and curling of the leaves in irregular growth. Usually confined to the greenhouse, it is caused by excess of water, lack of light, improper temperature, and especially by over- heated soil, and is readily controlled by careful management. Chlorosis. — The leaves show completely whitened areas. The cause is unknown. Mosaic. — Upon the tomato appears a mosaic, similar to that of tobacco. Aside from this ap- parent kinship little is known about it. TURNIP. See p. 165. Fig. 144. — Tomato anthracnose. After Heald. WATERMELON. See p. 178. CEREALS Cereal Smuts in General ^^^ Dark or black masses usually dusty, though sometimes compact, replace floral parts, grain, glumes (chaff), or in some cases involve the leaves and stem. The smut mass con- sists almost wholly of the spores of the causal fungus which gains entrance to the plants when they are in a susceptible condition of development, the time varying with different kinds of plants, and grows within the plant as an active parasite, drawing its nourishment from its involuntary host. When the host plant has attained the right age, and corre- spondingly, too, the fungus has reached its proper stage of maturity, the disease becomes apparent to the eye as the familiar smut. Smut spores under suitable conditions of moisture, food, and heat sprout, and produce smaller spores, sporidia, which, if they fall upon the right host plant in the proper period of its development, penetrate into it and grow. The host plant may or may not outgrow its enemy. In any event, its presence is not apparent to the naked eye until the period of maturity arrives again, and another crop of dark-colored spores is produced. Kinds of smut.^-^ — In all, something more than 600 species are now recorded. Over 205 of these are found in the United States, growing upon some 442 different kinds of plants, most of which are unimportant and wild; although some of them, such as the corn smut, onion smut, and the smuts of wheat, oats, rye, barley attack plants of high eco- nomic value and cause great damage. The yearly toll from three of these that are easily preventable has been estimated to be as high as 25,500,000 bushels of wheat, 110,000,000 bushels of oats, 6,000,000 bushels of barley. 266 Cereals 267 Negligence thus involves a total of more than 100,000,000 bushels of grain annually. The common corn smut develops upon any part of the corn plant, but is usually most conspicuous upon the ear and tassel. Another smut of corn growing only upon the tassel is less widely known. Rye smut develops mainly in the stem; the smut of oats, wheat, and barley in the ovary, the grain; onion smut grows upon the leaves, often in the bulb. It is evident that to know precisely what parts and at what periods the various crop plants are open to infection is of utmost importance in looking to the prevention of the smuts. It was earl}^ proved that oats are susceptible to infection only in the early stages of their development. The exact work of Brefeld proved that corn is susceptible to infection on all young, tender, growing parts, and in 1896 Maddox, Brefeld, and others showed that in the case of the loose smut of wheat and the barley smut infection occurs while the plant is in bloom, this infection affecting the seeds and resulting in smutted plants in the crop raised from such infected seeds. It is upon these facts that our present modes of preven- tion are based. The treatment for oat smut is such as to kill the spores adhering to the grain and thus prevent in- fection during the period of susceptibility, i. e., the very young seedling condition. The same treatment is effec- tive for the stinking smut of wheat. The loose smut of wheat gaining entrance to the plant before the grain is harvested cannot be prevented by such means without danger to the seed, but can be prevented by the use of clean, uninfected seed. Corn, being susceptible at all ages of its growth, cannot be protected by seed treatment. Owing to their great damage and conspicuousness, smuts have attracted attention from very early times, and many references to them are found in ancient writings. Probably not until 1791, however, was their true nature as vegetable parasites recognized. Many were the means that were 268 Diseases of Economic Plants suggested for the prevention of these pests: placing laurel branches in the field, change of seed, avoidance of manures, thorough screening, soaking in brine, etc. V}\ "/'V '■'')' ' /i * I! Fig. 145. — Oat plants, smutted and healthy; note difference in height. Preventive treatments. — One early remedy that has proved its value and remained in common use, soaking the seed in copper sulfate, was first tried by Tessier in 1789, after he, in 1786, and Young, in 1787, had tested numerous chem- Cereals 269 icals. His test was without results, since, during the season of his experiment, neither treated nor untreated wheat was smutted. Prevost of France in 1807 was the first to publish an account of the successful use of copper sulfate for wheat smut. He recommended a solution of about 6 per cent strength, and the remedy was, and is, still widely used. Solu- tions varying in strength have been employed, one-half per cent being most highly recommended. In 1873 Dreisch improved the copper-sulfate treatment by using limewater following the copper sulfate; thus, to a large extent, diminish- ing the amount of seed killed by the treatment. Jensen, a Dane, in 1887 and 1888 reported excellent results with oat, barley, and wheat smuts from dipping the seed in hot water. Untreated seed gave 36 per cent of smut. One-fourth per cent of copper sulfate gave one-half per cent smut. Warm water, 56° C. (133° F.) for five minutes, gave no smut. Kellerman and Swingle soon afterward in- troduced this last treatment into this country. In 1888 the germicidal action of formalin was discovered and this substance was used as a preventive for oat smut by Bolley of North Dakota during the years 1894 to 1897.3-1 The use of the various smut remedies is usually attended by an increase in vigor of the plants, and by an increase in jdeld in excess of that due simply to the elimination of the smutted grains. Thus increases of over 4 bushels per acre have been found in wheat fields in which only about \]/2 bushels were destroyed by smut. Similarly, with oats, the increase in yield is often five times as great as the quan- tity of grain lost by smut in fields not treated. This may be due to elimination of the fungus from plants which other- wise would have to resist it throughout a portion of their growth period or it may be due to the killing of spores of numerous fungi other than those of smut on the seed which exert an adverse influence during and following germination. An excellent account of the early history of smuts in general may be found in the Report of the Kansas Agricultural 270 Diseases of Economic Plants Experiment Station for 1889, and a comprehensive article upon corn smut in the Twelfth Report of the Indiana Agricul- tural Experiment Station. Present methods of seed treatment.^^^- ^^^ — Preliminary to any form of seed treatment, the seed should be thoroughly cleaned, in some cases floating-out of the spore-filled grains is necessary, and after treatment it should be protected from contamination. Sacks, bins, drills, etc., with which seed will come in contact, should be disinfected with formalin. The common methods of cereal seed treatment now are by formalin, hot water, or copper sulfate. The first is simpler and easier and is preferable whenever it is effective. In treating for certain kinds of smut, however, the formalin treatment is not so effective as is the hot-water method. These three methods with their limitations are as follows: The formalin wet method. — The seed to be treated is either dipped in the solution of formalin, 1 pint to 30 or 40 gallons of water, or this solution is sprinkled on the seed, with thorough mixing, at the rate of one gallon to each bushel of seed. The pile is then blanketed and later spread out to dry. In a modification known as the formalin dry method ^'-^ the seed is shoveled from one pile to another and each shovelful is sprayed or sprinkled with a solution consisting of, formalin (37 per cent formaldehyde) diluted with an equal amount of water, and applied at the rate of one quart (1 pint of formalin) to 50 bushels of seed. A quart sprayer is conven- ient for use. After treating, the seed should be blanketed for five hours, when it is ready for planting. Workmen will find the formalin irritating to the mucous membrane, and therefore should apply the solution as directly as possi- ble to the seed. A variation from this method is to mix 1 pint of formalin with 10 or 12 gallons of water and sprinkle on the seeds as they are shoveled over. They may then be sacked immediately and sowed next day. This method, employing a strong solution, seems to be both safe and efficient with oats, but its use with wheat and other grains is Cereals 271 still in the experimental stage and is apparently attended with danger to the seed. On a large scale, oats may be treated by the formalin method at the rate of 500 bushels an hour, by throwing the formalin solution, by means of a steam pump, against the grain as it falls through elevators arranged with deflectors so as to give proper con t act. ^"^ The formalin treatments as above given are effective against those smuts in which the spores lie upon the surface of the seeds and in which the smut fungus is not within the seed itself, e. g., oat smuts, wheat bunt, covered smut of barley and rye, rice smut, sorghum, and millet kernel-smut. Long time formalin treatment. — Seeds are immersed for two hours in the formalin solution, 1 pint to 40 gallons of water. Favorable results are reported even in those cases of floral infection where the hot-water treatment was formerly thought necessary, e. g., in the cases of wheat loose smut and the covered smut of barley, but complete reliability of this treatment for these diseases is not yet demonstrated. Copper-suifate treatment. — This is the oldest effective treatment of cereal seeds. It has, however, on account of its greater cost and the larger injury done to the seed, in the main been superseded by formalin methods. It is effective against the same smuts for which formalin is used, but is recommended only where there is heavy soil infestation. A solution of 1 pound of copper sulfate and 1 pound of common salt to 5 or 10 gallons of water is used, and the seed either soaked, sprinkled, or dipped. Treatment should be com- pleted by dipping or sprinkling with milk of lime (1 pound of quicklime to 10 gallons of water). The hot-water treatment ^^^ is employed for those smuts in which the fungus is within the seed, not superficial. There are three forms: 1, the short treatment; 2, the modified hot- water treatment; 3, the long treatment or pasteurization. The first consists, in general, in subjecting the seed to water at a temperature ranging from 52° C. (120° F.) to 61° C. (142° F.) for 10 to 15 minutes. It is of use in only those 272 Diseases of Economic Plants cases where formalin can be used, and will therefore not be described further. The directions for the modified hot-water treatment, drawn from Freeman and Johnson, ^'-^ with slight changes, are as follows: After the seed has been cleaned by thorough fanning and sifting, it should be soaked for from five to seven hours in water at ordinary room temperature, 17° to 22° C. (63° to 72° F.), then placed in small, loose sacks or wire baskets, containing not more than one-half peck each, and drained for a short time. The seed must be treated in small lots in order that all of the grain may quickly and uniformly reach the desired temperature. Two tubs or vats of water should be provided. In one tub (No. 2) the exact tempera- ture required should be maintained. The other tub (No. 1) is used for bringing the grain to the temperature of the treatment, so as not to lower the temperature in tub No. 2. Galvanized iron tubs of 20 to 40 gallons capacity, and kerosene or gasoline double-burner stoves, are convenient. The drained sacks or baskets of seed should be plunged into tub No. 1 for a minute, then transferred to tub No. 2, and kept agitated while immersed at temperatures and for the periods specified below, the temperatures mentioned being maintained as nearly as possible: For barley, 13 minutes at 52° C. (125.6° F.); for wheat, 10 minutes at 54° C. (129.2° F.). In treating barley, if the temperature should rise above 52° C. (125.6° F.), the time of immersion must be reduced to ten minutes at 53° C. (127.4° F.), or five min- utes at 54° C. (129.2° F.). Above 54° C. (129.2° F.) there is no safe margin. If the temperature falls slightly below 52° C. (125.6° F.), the time of treatment should be increased in proportion. A temperature lower than 51° C (123.8° F.) is not effective. In treating wheat, if the temperature should rise above 54° C. (129.2° F.) or fall below 52° C. (125.6° F.), the time for immersion must be diminished or increased ac- cordingly. Under no circumstances should a temperature of more than 55° C. (131° F.) be allowed. Temperatures be- low 51° C. (123.8° F.) are ineffective. A reliable thermometer Cereals 273 is necessary, since the use of an inaccurate instrument may result in injury to the germinating power of the grain or in failure to prevent the smut. At the end of the period of treatment, the grain should be transferred to a cold bath to terminate the action of the heat. Two men working together can easily treat one bushel of grain an hour, or enough seed in one day to sow a seed waterS-r ( jBoiling water. Post. Fig. 146. — Diagram showing a convenient arrangement of utensils for the Jensen hot- water treatment. After Swingle. plat of from 6 to 10 acres. The seed may be dried by spread- ing it out in thin layers, not over 5 cm. in depth, on a clean granary floor or on canvas, and shoveling or raking it from time to time. It should not be allowed to sprout. Care must be taken to prevent freezing of the grain when it is moist, as this will impair germination. 274 Diseases of Economic Plants Seed treated as indicated may be planted as soon as it is sufficiently dry to run freely through the drills, making al- lowance for the swollen seed. The long hot-water treatment or pasteurization consists in subjecting the seed to a temperature of 45° C. (113° F.) for three hours, the permissible range being 44° to 46° C. (111° to 115° F.). The advantages of this method are greater effi- ciency, less danger of killing the seed, and the need of but a single bath. It is difficult, however, to maintain the proper temperature for so long a time. These hot-water treatments, though effective against both smuts of wheat and of barley, are used primarily for the loose smuts of barley and wheat, and are generally combined with the seed-plat, see p. 275, and rogueing. Hot-water treat- ments are much simpler and more accurate of application if steam is available for heating purposes. Injury to seed by treatment. — The germinating power of treated seed should be tested, and if low, the rate of planting should be correspondingly increased. The formalin treat- ment does but inappreciable injury to sound seed, though cracked seed are injured by chemicals. The softer wheats are more often cracked than the harder varieties, therefore are more liable to injury by chemical treatments. Seed sub- jected to wetting may be injured in germination power if dried too slowly. However, poor stands attributed to seed injury often are really due to the use of too little seed, since the treated, swollen grain feeds more slowly through the drill. The sensitiveness of various seeds ^^^ to treatments is indicated in the following table. shows no injury, tr a trace only, H — I — h very serious, -\ — f- less serious. It is to be added, however, that some experimenters report injury to wheat from the dry treatment. Wheat Rye Oats Barley Formalin Dip Sprinkle Dry Soaking 1 hour Cereals 275 Wheat Rye Oats Barley Copper sulfate 10 minutes • + + + tr Long time + + + + + + Hot water 133° 12 minutes + + + + + + tr 101-115° 3 hours tr tr Modified 129° 10 minutes + + tr The Seed Plat. — A good, clean, well-cultivated piece of land should be selected for raising seed. The plat should be large enough to provide at least twice as much grain as will be necessary for farm seed the following year in order to allow for loss in cleaning and selecting. This seed plat should not lie near fields of smutted crops of the same cereals, nor should it be so located that the prevailing winds at flowering time can carrj^ spores to the seed plat from a neighboring field of the same grain. This isolation is absolutely necessary. A strip of wood, a cornfield, or a large meadow is a valuable protection. In this plat should be planted seed treated by the hot-water methods. The seed plat may be maintained from year to year, as long as any smut is present in the grain fields. Cereal Rusts in General ^-^ The rusts constitute a complex, intricate, difficult, but interesting group of diseases. It is said that the ''average annual loss from rust throughout the United States far exceeds that due to any other enemy, insect or fungous, and often equals those from all others combined." The black-stem-rust alone in the United States and Canada in 1916 was estimated to have caused a loss of about 280,000,000 bushels of wheat and additional loss on oats, barley, and rye. The rusts in their most complete form exhibit three dis- tinct stages (cf. p. 150). The spring stage, or cluster-cup, consists of a group or cluster of very minute, cup-like, spore- 276 Diseases of Economic Plants bearing regions. These cups are sunken in the tissue of the host, often with their rims only protruding. The second, or summer, stage, also called the uredinial stage, is of entirely different appearance, consisting usually of elongated sori, bearing a mass of spores the color of iron rust or verging toward orange or yellow. These spore masses are at first covered by the epidermis of the host, but this covering eventually ruptures, disclosing the usually dusty or pul- verulent mass of spores, surrounded by a fringe of the re- maining epidermis. The third, winter or telial, stage consists of sori almost exactly like those of the uredinial stage except that the spores within are usually darker in color and in a compact, cushion-like mass. The sorus is often identical in the two latter stages, a uredinium gradually changing as the season advances into a telium. These three stages have, in general, three separate func- tions. The function of the teliospores is to live over winter or over the long resting period of the fungus. They are essentially long-lived and hardy. The cluster-cup spores multiply and spread infection, especially in the earliest part of the season. The urediniospores continue the multiplica- tion and infection throughout the growing season of the host. The last two forms of spores are in general comparatively short-lived. If the host plant remains alive over winter, as is the case with winter wheat, the fungus, in the South, may continue to grow and produce summer spores throughout the winter. Even in colder climates the urediniospores of some rusts live over winter and start infection in the spring. In the case of some rusts these three forms are all known to be present. In the case of other rusts one stage or even two stages may either be unknown or may not exist at all. When all three stages do exist, the spring stage often develops upon some host other than that bearing the uredinial and telial stages. Thus the spring stage of the wheat rust is found upon the barberry; of corn upon oxalis; of oats upon buckthorn. Cereals 277 That some intimate relation existed between the bar- berry bush and the black-stem-rust of wheat was suspected very early in the seventeenth century, and in 1660 a barberry eradication law was passed in France, while between 1726 and 1779, Connecticut, Rhode Island, and Massachusetts did like- wise. In 1818 Schroeter, a Danish school-teacher, published man,y observations concernin^e; the relation of the cluster-cup upon the barberry and the rust of grains. This relation was finall}' definitely proved b}^ De Bary in 1865, who, by sowing the teliospores from the wheat upon the barberry, produced the cluster-cups. Some rusts are closely limited in host range and can grow on very few, perhaps on only one host ; others are able to grow on various hosts. The host relation of several important cereal rusts is shown in the following table : ^^^ 33 53 ■*o 55 Also on other genera of grasses CO O tr 1. + as below Puccinia + + Agropyron sps., Elymus 3 sps., graminis Hordeum 4 sps., Hystrix 1 sp., secalis Secale 1 sp., Sporobolus 1 sp., Bromus 2 sps., Avena saliva and Triticum, vulgar e. Puccinia + tr + + Agropyron 7 sps., Elymus 5 sps.. graminis Hordeum 5 sps., Hystrix 1 sp., tritici Siecale 1 sp., Triticum 8 sps., Bromus 3 sps., Alopecurus 1 sp. Puccinia + tr tr tr + Ave?ia 2 sps., Agrostis 3 sps., graminis Anthoxanthum 1 sp., Dactylis 1 avence sp., Kloeeria 1 sp., Panicularia 1 sp., Arrhenatherum 1 sp., Alope- curus 2 sps., Bromus 3 sps., Cala- magrostis 1 sp., Holcus 1 sp., Phalaris 1 sp., Agropyron 1 sp., Beckmannia 1 sp., Elymus 2 sps., Festuca 2 sps., Hordeum 3 sps., Hystrix 1 sp., Lolium 3 sps., Phleum 1 sp., Secale cereale. 278 Diseases of Economic Plants Q 55 ?5 S3 Also on other genera of grasses -2 'S c as below O tr Qq 05 tr + Puccinia tr Dactylis 1 sp., Festuca 2 sps., graviinis Koelerixi 1 sp., Phleum 1 sp., Alo- phleipra- pecurus 2 sps., Holcus 1 sp., tensis Avena 2 sps., Arrhenatherum 1 sp., Bromus 1 sp., Elymus 1 sp., Hor- deum 2 sps., Lolium 2 sps., Secale cereale. Puccinia tr tr tr + Agrostis 3 sps., Alopecurus 2 graminis sps., Bromus 1 sp., Dactylis 1 sp.. agrostis Holcus 1 sp., Koderia 1 sp., Avena, 1 sp., Calamagrostis 1 sp., Hor- deum 1 sp., Secale 1 sp. Puccinia Aira ccespitosa, A. hottnica. graminis airce Puccinia Poa compressa, P. ccesia, P. pra- graminis tensis. poa Puccinia + tr + + Agropyron 7 sps., Elymus 4 sps., graminis Hordeum 2 sps., Triticum 7 sps.. tritici- Bromus 1 sp., Secale 1 sp. compacti Puccinia + simplex Puccinia + tr + Alopecurus 1 sp., Anthoxanthum coronata 1 sp., Avena 1 sp., Dactylis 1 sp., Elymus 1 sp., Hordeum several species. Puccinia tr dispersa Puccinia tr Sorghum vulgare, and *9. holo- purpurea penses. Puccinia + triticina Puccinia + + + glumarum + =host 0=no infection tr=rust infects weakly Cereals 279 All cereal rusts multiply much more rapidly in damp than in dry weather, and are more destructive to late crops. There is no evidence that these maladies can be carried by seed from rusted plants, though such seeds should not be used for seed purposes, since they do not have stored nourish- ment sufficient to give the seedling a vigorous start. Great difference in rust resistance has been shown; thus while one variety of grain was so badly affected as to yield only 23^ bushels per acre, a resistant variety under the same conditions gave 383^ bushels. The greatest hope lies in the use of varieties which can resist the disease. A number of different kinds of grain are now known which possess sufficient resistance to give good yields even when the rust is in its worst form. Since serious outbreaks of rust must be looked forward to with certainty, the item of rust resistance must have due weight in the selec- tion of the variety to be grown. Several varieties of oats of the red group, among them the Burt, Appier, and Cook when grown in the Southern States, are known to possess valuable resistance to the oat rust. Similarly there is large difference betvv^een varieties of wheat as to rust susceptibility. Early maturity in oats is of especial value in that it enables the plant to evade the heaviest part of the rust attack. Good drainage and clean culture conduce to plants of more resistance to rust, as does also good preparation of the seed bed. Drilled wheat is better lighted and better ventilated and resists rust more effectively than wheat that is broadcast. Wild grasses that harbor rusts identical with the rusts of crop plants, such as wild meadow oat grass, orchard grass, wild wheat grasses, quack grass, wild rye grasses, etc., may propagate the fungus and increase infection. If such grasses are rusted, they should be burned, plowed under, or avoided in the location of the grain fields. While sprays of various kinds may be effective in checking the spread of rusts, the use of such means of prevention is impracticable, owing to the nature of growth of the crop, 280 Diseases of Economic Plants and the difficulty and expense of the application. Moreover the question of use of such treatment is complicated by the different kinds of rusts to be met and by their different behavior in different seasons. Anthracnose of Cereals Anthracnose ^^^ {Colletotrichum cereale Manns) . — Upon many cereals and forage crops, as rye, wheat, oats, orchard grass, timothy, red-top, and blue-grass, occurs a blight, resulting in shriveling of the grain and spotting of the leaves and stalks. The fungus is marked by small, black acervuli, located upon the spikes, stems, and sheaths. The chief at- tack is made as the plants approach maturity. For further discussion, see rye. Special Diseases of Cereals BARLEY. Loose-smut ^^^ {Ustilago nuda (Jens.) K. & S.). — This disease, previously thought insignificant, seems to be in- creasing in importance. It now often causes losses in Wis- consin and Minnesota of from 5 to 10 per cent of the crop, and is generally prevalent in this country, though often unnoticed on account of the early season of its development, and its absence at harvest time. Every spikelet of the smutted head is usually affected and entirely changed into smut, the central stalk of the head alone escaping. Adjacent leaves are also occasionally smutted. The smut masses, when they first appear, are covered by a white or gray membrane which soon ruptures, loosing a powdery, olive-brown mass of spores, which soon blow away. This character enables one to distinguish it easily from the covered smut. Smutted plants head early, the smut reaching its maximum at flowering time, though scattered heads of smut may appear at other periods. The smutted heads stand high on tall stalks, which affords ex- cellent wind distribution of the spores to the surrounding Cereals 281 blossoms. The fungus, reaching the blossoms, gains such foothold upon the developing grain that its use as seed, with- out treatment, insures a smutted seedling as offspring. In Fig. 147. — Loose-smut of barley in various stages of development. After Johnson. the plant developing from such an infected seedling the disease does not show externally until the smut ripens at the next blossoming season. The life history of this smut is thus similar to that of 282 Diseases of Economic Plants wheat loose-smut, and the same treatment, i. e., rogueing, combined with a modified Jensen hot-water treatment, is effective. See p. 272. Covered-smut^-'' (Ustilago hordei (Pers.) K. & S.). — ■ In the covered-smut, the smut masses replacing the grains and glumes are at first covered by a membrane composed of the outer surface of the glumes of the spikelet. This mem- brane retains the spores for some time after harvest. The spores, as seen en masse, after the rupture of this cover are very dark to purplish black, with no tint of olive. The formalin treatment applies here. Ergot. See rye. Black-stem-rust (Puccinia graminis Pers.). — The forms oc- curring on both wheat and rye develop equally well on barley, and severe attacks of either form are common. See wheat. Dwarf -leaf -rust (Puccinia simplex (Koern.) E. & H.). — Reported from Iowa in 1896, later from California, Minne- sota, Virginia, Wisconsin, Wyoming, and Maryland, this rust seems to be of recent introduction and generally of minor importance, though serious in the extreme West. Blight ^^^ (Pseudomonas translucens J. J. & R.). — Water- soaked areas appear on the leaves extending in longitudinal stripes or blotches between the veins. Later they turn brown. Small, gray drops of exudate appear on either leaf surface. Distortion of the head may be caused by disease of the en- veloping leaf. It has been observed in nine states from Ohio to Oregon, on many varieties of barley. Infection ap- pears to be by means of the seed. Stripe-disease (Pleospora gramineum Diet., Helmintho- sporium) . — This leaf blight was discovered in America by Pammel in 1890. It is characterized by longitudinal, yellowish-green spots in parallel rows upon the leaves. The plants die prematurely, and the yield is thus reduced. It is reported from many states. The loss in some fields amounts to from 10 to 50 per cent of the crop. Stripe is almost en- tirely prevented by formalin seed treatment (1 pt. to 30 gals., 2 hrs.). Cereals 283 Net-blotch ^^' {Helminthosporium teres Sacc). — First known in the United States in 1907, this disease has been observed in Iowa, South Dakota, Minnesota, and Sas- katchewan. It occurs as brownish, circular, or somewhat elongated dark spots which soon cause the leaves to turn brown. It also occurs upon sheaths, glumes, spikelets, and grain. The straw at harvest is dull brown and lacks strength. Scab, Powdery-mildew, Yellow-stripe-rust. See wheat. BROOM CORN Kernel-smut ^^^ {Sphacelotheca sorghi (Link) Clinton). — Irregular, elongated branches of inferior value indicate the presence of the smut. The branches are further damaged by blackening occasioned by the loose spores. The seeds are destroyed. Of the fields examined by Clinton in Illinois few showed over 1 per cent of the stalks infected, though some- times parts of a field })ore as high as 20 per cent of diseased stalks. Infection can occur only upon very young plants. Between the times of infection and the appearance of the smut masses in the panicle no signs of the disease are seen without the aid of the microscope. The smut can be prevented by the use of clean seed, obtained either from clean fields or by disinfecting the seed by the hot water (58° C. (135° F.) for 10 to 15 minutes) or formalin methods. CORN, TEOSINTE Smut^^^ (Ustilago zeoe (Beckm.) Ung.). — Corn smut is well known to every farmer, occurring wherever the corn plant is grown, as black, pulverulent masses most conspicuous upon the ear and tassel. The damage in 1917 is estimated at 108,000,000 bushels. In Iowa a loss of two-thirds of the crop was at one time reported. Corn smut is first mentioned in literature in 1754, and the first record of it in America is in North Carolina in 1822, Experiments looking to its prevention were made 284 Diseases of Economic Plants as early as 1760. The disease may attack any part of the plant at any age, — leaves, stalks, aerial roots, ears, tas- sels, — provided only that they be still in tender growing condition, not mature and hard. The first symptom is a pale, glistening, swollen area covered with a white mem- brane, which soon ap- pears black owing to matured spores within. The mem- brane eventually bursts, loosening a powdery, dry, black mass of spores through which fibrous veins of the corn plant still penetrate. It has been conclu- sively demonstrated that the causal fungus is not conveyed to the new crop in the seed, as is the case with so many other smuts, and that there- fore no form of seed treatment is of value for its prevention. It has been clearly shown that infection is produced by the spores which, under suitable conditions of moisture, fall upon any tender part of the corn plant. The silks furnish the requisite conditions, and it is through them that ear infection occurs. The Fig. 148. Corn smut upon the ear. Original. Cereals 285 sheaths of the leaves hold water, and inclosing as they do the tender growing portion of the stem, are admirably suited to infection. Since infection cannot occur without moisture, weather conditions are of predominating influence. Fig. 149. — Smut upon sweet corn tassels. After Jackson. The longer the crop grows, the longer the period of sus- ceptibility is maintained. Thus a late-planted crop in In- diana showed half as much infection as a crop which was 286 Diseases of Economic Plants planted earlier, chiefly -because it was exposed to contagion only about half as long. Moisture and richness of soil predispose to disease by increasing growth and giving a greater number of susceptible points of attack. Corn thickly planted is more liable to infection because ventilation is restricted, and thus a more humid atmosphere is maintained around the plants. It has been shown that corn smut can be reduced by spraying with Bordeaux mixture, but the saving does not warrant the expense. To go through the field several times during the season and cut out and burn all the developing smut masses that can be seen, thus to destroy the spores and prevent the continued spread of the disease, is recommended, but the actual utility of such practice has not been demon- strated, though it is probable that this practice continued yearly would result in continued diminution of smut. The use of the silo in which the smut spores are rendered non- viable tends to lessen the amount of smut. The smut fungus can live and even increase in manure. Therefore live smut spores may infest the manure pile and thereby increase the disease in fields to which such manure is applied. The smut itself, contrary to popular belief, is poisonous to stock only under very rare and exceptional conditions, so rare as to be practically negligible. Fresh smut balls that have not yet turned dark are edible, and, prepared as mushrooms, are delicious. Head-smut (Sphacelotheca reiliana (Kuehn.) Clint.). — This smut, identical with that of sorghum, occasionally occurs upon corn and is somewhat more injurious though less common than the usual corn smut. It cannot be controlled by seed treatment. Corn Ear Rots ^^^ Four types of ear rot, due to four distinct diseases, are described below. In the aggregate the loss from these is enormous, constituting as it does 10 per cent or more of a crop annually. Infection comes from definite species of Cereals 287 fungi, and is not comparable to ordinary molding of dead organic matter by fungi of varying kind. Dry-rot {Diplodia zece (Schw.) Lev. and Diplodia macrospora Earle) . — This is one of the very widespread, dry ear rots of corn variously known to growers as mold, mildew, rot, dry-rot, etc. Though the disease is really present soon after silking, and even much earlier from root infection, it is not usually recognized until husking, when a whitish covering of the kernels within the husk is noted. This white mycelium also forms dense masses between the indi- vidual grains, among the husks, and over the cob. The grains on the affected ear are shrunken, loosely attached, light in weight, darker in color, and more brittle than those of a healthy ear. Upon breaking open an ear, very small black pycnidia may be seen embedded in the white masses of mycelium, especially at the bases of the kernels. Diseased ears left in the field may develop these pycni- dia in such abundance as to make the grains black. Much of the food value of the corn is lost, owing to the consumption of starch within the grain, as well as to the pre- vention of starch storage. The germi- nating power of the grain is also lost. Upon the stalks the fungus first appears as very small dark specks under the rind, near the nodes, and at broken places, usually in over-wintered stalks. Three-year-old stalks have been found Fig. 150. — Young ear of com inocu- lated in the silk with Diplodia. Af- ter Burrill and Barrett. bearing pycnidia. 288 Diseases of Economic Plants Although the green stalks are not naturally susceptible, the shanks are particularly so. The causal fungus gains entrance to the ears from attacked stalks which bear them, and these are in turn infected Fig. 151. — Diplodia on old shanks. After Burrill and Barrett. through the roots from the soil. Ears are also invaded through the silks by wind-borne spores, which come, in part, from diseased ears, but more largely from diseased stalks left in the field. Cereals 289 Any method of reducing the amount of infective trash, par- ticularly old stalks near or in the fields, aids in control of this pest. Practically, this means to take out of the field and destroy all rot-infected ears and to cut in- fected stalks low and haul them away or burn them. It is still better to practice such rotation that corn will not follow corn within two years. Dry-rot (Fusarium sps). — Upon the ears this disease ap- pears as a dense, felted, white mycelium, extending between the kernels to the cob. The kernels are killed and their starch partly consumed. A second Fusarium disease is characterized by a deep pink to red color noted on the ear when the husks are removed. The kernels are brittle and the starchy portion within is powdery. A third Fusarium disease causes less complete destruction of the ear than the preceding; often only a few scattered ker- nels are affected. The mycelium is white and sparse. A cob- rot ^^^ due to Coniosporium softens the cob without mate- rially injuring the grain. Root-rot, stalk-rot =^1^' ^0^' ^0^' ^-^ (Fusarium sps.). — The first record of root and stalk-rots of corn was made in 1907 by Fig. 152. — Corn mold caused by Fusarium. After Burrill and Barrett. 290 Diseases of Economic Plants Selby, in Ohio. In 1914, Pammel, in Iowa, called attention to a serious root-rot of corn caused by a Fusarium. The disease is now known to prevail generally throughout the corn belt both in the South and the North. Though no ac- FiG. 153. — Rotten stalk and the nubbin re- sulting. After Hoffer. curate estimate has been made of the amount of damage, it is known that the loss is large. Among the symptoms are: 1. Poor stands due to missing hills, caused by defective germination. 2. Weak and stunted seedlings, many of which may eventually die. Stunted Cereals 291 plants show decayed roots and purplish-brown discolored stalks when split lengthwise. 3. Down-stalks due to rotting of the roots, so that the plant falls over. 4. Broken stalks due to weakening, chiefly at the nodes. 5. Barrenness and nubbin formation. The infected plant lacks vitality to form a perfect ear. 6. Broken shanks due to rot. 7. Diseased kernels. The kernels may be molded and cracked, though no sign of disease may be apparent and the infection or weakening of the kernels shows only on germination. The severity of the attack depends upon the stage of develop- ment, the vigor and resisting power of the corn plant as determined by the conditions for growth and development, and by its heredity. Root-rot is caused by fungi, mainly Fusarium, and arises chiefly from primary infection, from infected seed, though to some extent from secondary infection in the field. The planting of infected seed is largely responsible for missing hills, down-stalks, nubbins, and other signs of disease. No infected corn should be used for seed. To eliminate the infected seed, special adaptation and care in using the rag- doll tester, or the use of special testers, devised by Hoffer, is necessary, whereby the seedlings that show infection, when less than three inches in height, may be recognized and the ears from which they originated discarded. Since the wheat scab organism (Giberella) causes rot of stem and shank of corn, corn so diseased increases the amount of wheat scab in succeeding crops. Wilt ^^^' ^^^ {Pseudomonas stewarti EFS.). — This corn wilt was first described by Stewart as prevalent in nearly all parts of Long Island upon many different varieties of sweet corn. In some cases the entire crop was ruined, and 20 to 40 per cent of loss was frequent, though in the majority of cases the loss was so slight as to pass without notice. It has been noted on sweet corn in Kentucky and Illinois, but rarely on field corn. The diseased plants wilt and dry up much as though from lack of water, yet in soil that is amply supplied with water. 292 Diseases of Economic Plants While the wilting is most likely to occur at flowering time, it may appear at any stage of growth when the plants are 25 cm. or more in height. In mild cases the lower leaves wilt first, while in severe cases all wilt at one time. The death of the plant may occur in four days after the first signs of disease, or may be delayed a month, possibly with recovery and relapse intervening. The roots remain normal, but the veins in the stems appear as yellow streaks, in older cases black, instead of their normal color. Such stems, if cut crosswise, shortly exude a yellow, viscid drop at the ends of the veins. This is the most distinctive character, and infallibly indicates the presence of the wilt. Death is caused by the plugging of the water passages with this viscid substance, which con- sists mainly of bacteria. In the fields the diseased plants, representing young and old stages of infection, grow side by side with normally healthy plants. Health and disease may appear, even in the same hill; yet there appears to be no direct plant-to-plant infection, nor any of that centrifugal spreading from a diseased center that is so noticeable in most wilt or soil-borne diseases. The causal organism is found in the seed from affected plants, and it has been proved experimentally that such seed carries the disease to the offspring. As a preventive measure resistant varieties should be selected for planting, and all seed from plants which are at all diseased should be avoided. The disease may be carried from one locality to another by any of the means suggested under soil diseases, and especially by manure infested with stalks of diseased plants. Minor diseases Brown-spot ^^^ (Physoderma zece-maydis Shaw) was first noted in India in 1910, in Illinois in 1911. Its distribution is shown in the accompanying map. (Fig. 154.) Considerable damage is done in the region indicated by the darker shading, Cereals 293 but it is hardly probable that this disease will extend seriously or become very destructive, except locally, and in very humid, hot seasons. In some cases, the injury is as high as 6 to 10 per cent of the crop. The fungus grows in leaf, sheath, and stem, rarely in the husks. Bleached or yellow spots about 1 mm. in diameter first appear, and within a few days darken, eventually becoming reddish-brown. Coales- FiG. 154. — Map showing the distribution of Physo- derma zea3-maydis in the United States. Broken hnes, P. zeae-maydis present: solid line, P. zeae-maydis caus- ing damage. After Tisdale. cence of many spots may lead to discoloration of large areas and a rusted appearance. These diseased areas are often in bands across the leaf. Leaves are often killed. The dry epidermis eventually ruptures over diseased spots and the dusty, brown spores are freed. Diseased stems break easily, resulting in considerable lodging of the corn. General san- itary measures are recommended, chiefly destruction of in- fested refuse and rotation of crops. 294 Diseases of Economic Plants Blight ^^'^ (Pseudomonas sp.). — This disease was described by Burrill in 1889. It shows chiefly as a dwarfed condition which may occur in spots in the field, varying in size from a few square rods to an acre or more. The affected plants finally turn yellow, and most of them die. The lowest roots of dis- eased plants, in some cases comprising half of the root system, die. The stalk near the base, when split lengthwise, shows a uni- form, dark color which also appears in the upper nodes in lesser degree. Rust (Puccinia sorghi Schw.) . — Corn rust seems to have taken its place in literature in 1815. It is comparatively of slight importance, since it does not usually develop early in the season, though in exceptionally favorable climatic conditions it may do so. The brown sum- mer spores appear first in linear sori, and the black winter spores come later in the season. The cluster- cup stage is found upon the wood sorrel (Oxalis). Yellow-leaf ^^^' ^^^ (Helminthosporiurn inconspicuum C. & E.). — This blight gives a somewhat frostbitten ap- pearance to the plants, producing also a thin olive-green Fig. 155. — Portion of corn leaf show ing sori of rust. Cereals 295 mold upon the lower sides of the leaves. Sometimes only the tips of the leaves are affected, but usually whole leaves die. Yellowish, elongated spots limited by the veins, sometimes covered with dark-colored spores, are produced. The disease is confined almost entirely to late-planted corn, and is prevalent during its early growth, though it has never been reported upon seedlings. It is known to cause much loss in Delaware, New York, and Connecticut, and is of widespread occurrence in the United States. Chlorosis appears to be related to the mosaics in that it is transmitted by sap or by contact. It occurs also in the embryo. Two species of Sclerospora cause considerable injury to corn in Italy, and have been collected in the United States. The tassel is chiefly affected. Phyllachora causes damage to corn in the warmer climates. In the Orient very great loss is caused by a downy-mildew (Peronospora) . EMMER, EINKORN. See p. 310. KAFIR. See p. 307. MILLET Leaf-spot ^"^ (Piricularia grisea (Cke.) Sacc). — Upon the lower leaves the disease occurs as a spot which is at first dark purple or reddish, and elongated parallel with the length of the leaf. Later the center turns black and finally straw- colored, bordered by a black ring which merges into reddish- purple at its outer edge. Badly diseased leaves turn yellow, dry and shrivel from the tip toward the base, lessening the fodder value and seed yield of the plant. Smut {Ustilago crameri Koern.). — This smut infects the individual flowers of the fox-tail millets, destroying the lower parts of the glumes and the grain. It has been noted in Ohio, Minnesota, Connecticut, Illinois, Indiana, Iowa, Maine, Michigan, Colorado, North Dakota, and South Dakota. U. panici-miliacei similarly affects the Panicum millets. 296 Diseases of Economic Plants The formalin treatment, 1 pint to 40 gallons, is applicable to both of these smuts. MILO. See p. 307. OAT Loose-smut ^-'^' 2^3-345 (jjstilago avence (Pers.) Jens.). — Under the name "smut/' ''blackheads," etc., this disease is known wherever oats are grown. Grain and more or less of the chaff are replaced by a powdery, black mass, which shat- ters out as it ripens, leav- ing later only the naked branches of the panicle. Usually all the spike- lets of a head and all the heads of the affected plant are smutted. There is considerable dif- ference in the resistance offered by different va- rieties, but in view of the perfect protection af- forded by proper treat- ment this is of little significance. The damage caused by smut is commonly under- rated. In 1884 Arthur in New York by actual count found the oat smut to constitute from 8.5 to 10 per cent of the Fig. 156. — Loose smut on oats. After ordinary crop. By ac- Jackson. tual count of nearly Cereals 297 11,000 heads Plumb in 1886 determined the amount of smut to be 8.4 per cent; in some fields he found as high as 20, 28, and even 30 per cent. Kellerman and Swingle, counting smutted heads in Kansas, found different fields to have 8, 15.3, and 18.3 per cent of smut, while single portions of a field showed as high as 30 per cent. The loss in this country in 1917 was estimated as approximately 91,000,000 bushels. The reasons for underestimation of oat smut are: 1, the dwarfing of many of the affected plants, which thus re- main unnoticed by a casual glance over the field; 2, the fact that many smutted panicles remain invisible unless unrolled from their enveloping leaves. It was proved as early as 1858 that infection can occur only upon the very young oat plant; that older plants are immune. It was later determined by Brefeld that the plants are immune after the leaves have protruded 1 cm. beyond the leaf sheath. From this and other experiments it follows that practically all infection comes from smut spores which are upon the seeds when they are planted. These germinate, producing sporidia which infect the young plant. The fungus develops in these plants throughout the season without conspicuous effect until, at blossoming time, the fungus seeks the ovaries and the glumes and appears again as the familiar black spore masses. Any treatment which kills the spores upon the seed with- out materially injuring the seed itself results in a clean crop. The copper sulfate treatment endangers germination of oats. The hot water treatment is less convenient than the formalin treatments which are thoroughly satisfactory. See p. 270. Covered-smut (Ustilago levis (K. & S.) Magn.). — This differs from the loose smut in the less complete destruction of the flowers and in its less dusty spore masses, which are also blacker than in the loose smut. The smut masses are usually limited to the parts within the flowering glume and the palet or to the bases of these. The treatment is that given for loose smut. 298 Diseases of Economic Plants Black-stem-rust (Puccinia graminis avence E. & H.). — The black-stem-rust on oats shows but slight differences from the black-stem-rust of wheat, but it is racially distinct (see p. 277) and a field of one of these crops may be badly affected by its fungus, while adjacent fields of the other crop show no rust or indication of infection such as they might be supposed to do were the two rusts identical. As with the wheat black-stem-rust, its at- tacks fluctuate greatly in abundance and destructiveness from year to year. Crown-rust (Puccinia coronata Cda.). — This rust is found only upon species of oats and closely related grasses and in the telial stage clearly differs, even to the naked eye, from the oat rust mentioned above. It occurs upon oats in practically all fields but is more injurious in its southern range. The damage is not serious, or very rarely so. The cluster-cup stage is known to grow upon the common buckthorn (Rhamnus cath- artica) and the lance-leaved buckthorn {R. lanceolatus) . The yellow uredinial stage is most conspicuous. Later the black telia ap- pear under the epidermis as long streaks which, unlike most rusts, do not rupture the epidermis. Marked varietal resistance is shown. In California black oats are reputed to be less subject to rust than white oats. In the North, the White Russian is said to be resist- ant, while in the South, the red oats resist attack. Minor diseases Scab. See wheat. Leaf-spot (Phyllosticta sp.). — Browned or reddened leaves, with the black pycnidia profuse upon the Fig. 157.— Cov- ered-smut on oats. After Jackson. Cereals 299 affected surfaces, sometimes so abundant as to lend a blackish hue to the leaf, comprise the diagnostic symptoms of this malady. Eventually the leaves are killed. Blight ^^^' ^^^ (Pseudomonas avence Manns) . — A disease prevalent throughout the Eastern and Central States was attributed to bacteria by Galloway and South worth in 1890. It appears when the plants are only about 10 cm. high, first causing the leaves to turn brown and die at the tips, then throughout their length. The affected plants revive, but are so reduced in vigor as to prevent effective stooling, and a loss of from 35 to 75 per cent of the crop commonly occurs. The disease was carefully investigated by Manns, who claims that it is caused by the symbiotic action of two species of bacteria, a Pseudomonas and a Bacillus. Manns describes the disease as follows: The preliminary effect is yellowing of the leaf, beginning either as small, round lesions on the blade, or as long, streak- like lesions extending throughout the blade and even the whole length of the culm and blades. Occasionally it begins at the tips and works back into the culm; again the upper leaves often break down due to a weakened condition of the plant from defoliation below. The ultimate symptoms, wherever the disease has made much progress, are partial or general collapse of the leaves, which take on a mottled to almost red color. It prevails from New England to Georgia, and from the Atlantic to Indiana and Illinois. The damage in Ohio has been estimated at from 14 to 37 per cent of the crop. Rain and moisture favor it. When prevalent, the soil may become infested as in typical soil diseases. The only hope seems to rest in resistant strains. Halo-blight (Bacteria). — Oval, chlorotic areas 1-2 cm. in diameter, bordering a minute, sunken, dead center, occur in the leaf. Stripe-blight (Bacteria). — The diseased tissues are water-soaked, translucent, with an abundant exudate and 300 Diseases of Economic Plants no halo. The spot is long and narrow, between the veins. Anthracnose (Colletotrichum cereale) . — The effect of this disease upon oats is similar to that described for rye. Yellow- leaf {Hebninthosporium inconspicuum C. & E. var. hrittani- cum Grove) . — Oat leaves turn yellow and develop dark, brown, spore-bearing spots. Little is known as to its severity or prevention. Powdery-mildew. See wheat. Ergot occurs but rarely on oats. RICE 348 Blast, rotten-neck ^''^ {Piricularia cry zee Cav.). — This is a world-wide rice disease, which in Italy is controlled by the use of resistant varieties. It has probably been present for many years in American rice sections, but did not become of serious economic importance until about 1895. What seems to be the same disease occurs upon crab grass, and apparently infection may come from this host. It is reported from South Carolina and Louisiana, also from Texas, where it has been serious. The disease occurs upon upland as well as irrigated fields. The most characteristic symptom consists of lesions at the sheath nodes just over the joints of the stem, at the region where the stem comes to be the axis of the head (the ''neck region") and at the points where the blades of the leaves join their sheaths, appearing first as very small, water-soaked, sunken spots on the node of the sheath. Spots upon the neck are not water-soaked, and the skin does not rupture until the head breaks off. Later the spot becomes brownish or black, and similar discoloration runs upward and downward. The affected stem tissue gradually extends laterally, shrinks, and dies, cutting into or through the joint, which results in an open wound. The region above the wound becomes pale and dies. Upon young plants leaf spots occur, first brown with ashen center, later coalescing and taking the whole leaf. If the attack is early, the grain does not fill at all; if late, it may Cereals 301 partially fill. The dead portion of the plant may bleach or darken according to environment, resulting in varied char- acters in later stages of the disease. In 70 per cent of the cases examined by Metcalf the lowest joint of the rachis was affected, and in consequence the heads broke off at this point. This gives rise to the common name ''rotten-neck," but since the char- acter is not universal, the name is not an appropriate one. The chief damage results from the failure of the grain to fill on the diseased stalks. An early attack may render a crop entirely worthless. Plants attacked later, yield some grains which are of poor, light qual- ity, easily broken or blown away, and con- sequently largely lost in threshing and milling. The variation in size of the grain also largely depreciates the quality. Many of the heads, especially the heavier ones, fall off, and some fields show at least one-third of the crop thus left upon the ground. The Rice Committee of the Agricultural Society in South Carolina, March, 1904, estimated the loss, up to that time, to be very nearly $1,000,000. Depreciation in land values, necessitating abandonment of land, is a significant item of charge against this disease. The chief hope hes in the use of resistant varieties. Withholding nitrogenous ferti- lizers and removal of infective trash by burning are good sanitary measures. Green-smut {Ustilaginoidea virens (Cke.) Tak.). — This grain disease, though partaking of the appearance of a true smut, is in reality more closely related to the ergot of rye. Fig. 158. — Rice blast. After Fulton. 302 Diseases of Economic Plants The grains, usually only a few in each head, become en- larged, spherical, 5 mm. or more thick, and coated with a dark green powder. Some- times a yellow color prevails instead of the green. In sec- tion the interior is seen to be filled with a compact white mass bordered by a brownish yellow zone, then by the green coating. Though the disease has been known in Louisiana for ten or Fig. 159. — Rice showing "green-smut." After Fulton. more years, and is present to some extent in most fields, it is not considered serious, since rarely more than 0.25 per cent of the heads, and only a few grains per head, are affected. Black-smut ^''^ (Tilletia horrida Tak.). — A dark, unsalable flour, made from rice in the region of Georgetown, S. C, was reported in 1898. Anderson found that many heads of rice from these fields bore as much as 25 per cent of smutted grains. This smut was probably imported from Japan in infected seed, but due to the immediate action of Anderson and Walker the pest seems to have been completely stamped Fig. 160. — Rice showing black-smut. After Fulton. Cereals 303 out in South Carolina within the first few years after its advent. No reports whatever of its presence there have been made since 1903. It has since entered the United States through Louisiana. The smut closely resembles the stinking smut of wheat. The affected ovaries or grains are transformed into smut masses which remain within the glumes, and so resemble the normal grains as often to be mistaken for them. The fungous mycelium grows within the stem tissue of the diseased plant and, as is the case with wheat bunt, infection probably occurs in the seedling stage, the fungus remaining unnoticed Fig. 161. — Three rice spikelets: A, normal; B, smutted; C, glumes partly torn away ex- posing the spore mass. After Anderson. until its presence in place of the grain is disclosed as a black spore mass. The disease can be controlled by the method which stamped it out in South Carolina; that is, by the formalin treatment. Damping-off. — Two forms of damping-off of seedlings are known: 1. Rice, not covered, but simply flooded with water, frequently shows soft rot of the shoot in very young seedlings. 2. Covered rice often shows damping-off spots just above the surface of the ground. 304 Diseases of Economic Plants The causes of these rots have not been fully studied, but they are probably due to fungi or bacteria or both. Minor diseases Spotted-blight (Macrosporium sp.). — Small black spots of mold upon poorly filled grains sometimes occur, occasion- ally affecting field areas of considerable size. Speck, pip (Saprophytic fungi and bacteria). — The grain in some instances bears one or more discolored, often sunken, circular areas, 1-3 mm. in diameter, bounded by dark mar- gins with gray or pale-buff centers and often with a minute dark spot in the very center. In other cases the grain is shriveled and distorted without any definite spot. The interiors of the grains are chalky and brittle, and of such inferior quality as to be largely depreciated in value. Not infrequently from 10 to 25 per cent of the grain is affected, and in some cases nearly 100 per cent. The germinating power is much reduced. The disease is caused by the invasion of saprophytic fungi or bacteria into wounds caused by sucking bugs. Methods to control these insects have not been thoroughly worked out. Rust (Physiological) . — The leaves die gradually, begin- ning with the tips of the lower ones. Red spots and streaks usually appear before the leaves lose their green color. The roots are poorly developed, the plants dwarfed, and the heads small and light. RYE Ergot (Claviceps purpurea (Fr.) TuL). — Ergot is widely known as a black or purplish body, several times larger than the seed of the affected plant, which displaces the ovary or grain. Ergot occurs commonly upon rye and many other species of grass, as wheat-grass, wild ryes, blue- joint, Kentucky blue-grass, Canada blue-grass, red-top, timothy, and rye-grass. Of the last named, one farmer reports 1000 tons of hay so badly affected as to be worthless. Ergot is occasionally injurious on wheat. Cereals 305 This disease is caused by the attack of a fungus upon the ovary while the plant is in bloom. The fungus invades and consumes the ovary and replaces it with the ergot, which consists of a dense mass of tangled, interwoven mycelium, a sclerotium. Ergots, when mature and under suitable conditions, germinate, sending forth several stalks each, with club-shaped, knobbed tops. From these the spores issue to infect susceptible plants then in blossom. For some days the fungus spreads from blossom to blossom by means of other spores, and each infected ovary results in another ergot. Loss to the grain and the damage to the plant are slight. Chief injury from ergot arises from its effect upon cattle that are fed ergotized grain or graze upon badly infected grass. Animals become emaciated and rough-haired as the result of continuous feeding of ergot. Further symptoms of ergot poisoning are tardy circulation in the extremities, gangrenous sores upon the teats or mouth, and sloughing off of parts of the tail, ears, or hoofs. Abortion may also follow as an additional effect. Fields should be examined for the presence of ergot. If large quantities are found, the grass should not be used for hay or pasture. Ergot can be lessened by cutting susceptible grasses about flowering time, thus checking the spread of the fungus. Badly infested hay lands should be burned over to destroy sclerotia ; roadside grasses should be cut often enough to prevent the formation of ergot, and seed should be exam- ined to prevent the spread of ergot through this means. Seed may be freed of ergot by immersion in a 20 per cent solution of common salt, which will float the ergot to the surface. Black-stem-rust (Puccinia graminis secalis E. & H.). — The description given in connection with wheat applies here. Brown-leaf-rust (Puccinia dispersa E. & H.). — This rust bears a very close resemblance to the rust caused by Puccinia triticina upon wheat, but in careful inoculation ex- 306 Diseases of Economic Plants periments it has been impossi- ble to infect one of these hosts from the other. It is invari- ably present where rye is grown and is particularly abundant in the Southern States, though notwithstand- ing its universal presence it is not destructive. The uredi- nial mycelium remains alive in the South and continues to produce spores during winter in the leaf, as it probably does in colder climates as well. It is possible that it is in this way carried from season to season by volunteer rye in the fields. The cluster-cup stage occurs upon a member of the Borage family, but has never been found occurring naturally in America. Stem-smut ^-^' ^^^ (Urocystis occulta (Wallr.) Rab.). — Un- like many of the cereal smuts the stems and leaves as well as the floral parts are affected. It may be recognized by the usual, dusty, black spores, which occur especially at the joints. While this disease does not directly attack the grain, it does diminish the yield by weakening the plant. Loss from 25 to 40 per cent is reported in Minnesota, 60 per cent in Australia. Seedlings may be infected from spores \'^ \ |- \m m§/^ ' Am m 1 1 Im k "^ Fig. 162. — Head of rye attacked by anthracnose. After Manns. Cereals 307 in the soil. When serious, the formaUn treatment combined with crop rotation should be employed. Anthracnose ^^^ {Colletotrichum cereale Manns) . — A serious disease of cereals and other grasses, chiefly rye, wheat, oats, timothy, blue-grass, red-top, and orchard grass, was dis- covered by Selby and Manns in 1908. It is a destructive pest of very general distribution, being found in all the fields examined in Ohio. In one field it is estimated to have reduced the yield from 75 to 25 bushels, and it is assigned as a prominent cause of shriveling, such Fig. 163. — Normal rye kernels and shriveled ones due to anthracnose. After Manns. as is often attributed to rust, as well as of whitening and blighting of plants preceding ripening. Parts of the head above the points of attack die. The portion of the head that is killed is a total loss, and the general decrease in vigor of the plant results in shriveled, light grains. Upon stalks and leaf sheaths, beginning at the ground and extending over several internodes, the acervuli may be so numerous as to cause blackening. No remedy is known. Powdery-mildew, Yellow-stripe-rust and Scab. See wheat. Stripe-disease and Stripe-blight. See barley. SORGHUM, SUDAN-GRASS, KAFIR, MILO Blight {Bacillus sorghi Burr.). — This blight was studied by Burrill in 1883 and described in 1887. It prevails upon 308 Diseases of Economic Plants sorghum, broom corn, Kafir corn, and Milo maize, and has been noted in lUinois, Kentucky, Iowa, Louisiana, Ohio, Michigan, Nebraska, West Virginia, and District of Columbia, often in serious form. The chief character is irregular-shaped, elongated blotches of red, at first faint orange, upon the leaves and leaf sheaths, sometimes limited by the veins, and always more conspicuous on the inner than the outer sides. Smaller patches later blend, and the affected parts die and finally turn black. The lower sides of diseased spots upon the leaves often bear red incrustations, resulting from the dr3ang of the exudate from within. The roots show the same discoloration, and the outer parts of the rootlets die and become loose. If only slightly diseased, the plants may attain normal size. Badly diseased roots are evidenced by the yellowed tops and other signs of malnutrition. In advanced stages the roots give such poor anchorage that the plants may be easily pulled from the ground. Infected stalks should be burned and such rotation fol- lowed as to relieve the infested soil of susceptible crops for several years. Kernel-smuts ^^^ (Sphacelotheca sorghi (Lk.) CI., S. cruenta (Kuehn) Potter) . — These smuts infest the individual grains of the panicle, while the head as a whole remains nearly normal in appearance. The smutted grains are at first covered by a white, later gray, membrane. This membrane in time becomes broken by the winter exposure and frees the dark-colored spores. Kernel-smUt was reported by Kellerman in 1891 as limited to sorghum grown from imported seed. It was then known in the District of Columbia, Wisconsin, New York, Nebraska, and Kansas. It is widespread in Europe, Africa, and Asia, and was probably imported into the United States upon diseased seed. It was first recorded in the United States in 1884, and is now found in almost all places where sorghum is grown. According to Clinton's estimates it may prevail upon Cereals 309 from 4 to 32 per cent of the plants. The same investigator found that the yield in juice was lessened about 30 per cent, owing to the smaller size of the smutted plants. The damage is particularly serious in kafir and broom corn. See p. 283. These smuts gain entrance to the host only during the very young seedling state, before the plants appear above ground. The mycelium of the causal fungus grows through the plant until flowering time without any indication of its presence. At blossoming time the fungus seeks the ovary, destroys it, and becomes evident as smut. Disinfection of the seed by formalin is an efficient remedy. Head-smut ^^^ (Sphacelotheca reiliana (Kuehn) Clinton). — Instead of involv- ing the grains singly, as in the kernel-smut, the head as a whole is affected. A white membrane is at first present, but this later breaks open, exposing the pulverulent spore mass. Rarely, only a portion of the head is smutted. The spores soon weather away, leaving behind only the veins of the part involved. This disease was first noted in Egypt in 1868, and is preva- lent in America only in the Texas Panhandle. It occurs on sorghum and to some extent on corn. Milo is immune. The only procedure to recommend is that employed for corn smut. Anthracnose (Colletotrichum falcatum Went.). — Anthrac- nose was first seen in America upon sorghum in North Carolina, where it did considerable damage. It has since been reported from Louisiana. The spots which are more prevalent on the lower leaves have very definite gray or tan- colored centers which are surrounded by dark, reddish- FiG. 164. — Three views ot sorghum kernel- smut. 310 Diseases of Economic Plants brown rings, outside of which is the ordinary green of the healthy leaf. As the spots age they frequently grow together and form one large oblong area, sometimes several centi- meters long. At a late period in the development of the disease the centers of the spots are occupied by small black specks, the black acervuli of the causal fungus. TEOSINTE. See p. 283. WHEAT, SPELT, EMMER, EINKORN Black-stem-rust (Puccinia graminis Pers.). — Though in earlier years this rust was thought to grow indiscriminately upon a great variety of grasses, recent, thorough study has shown that what was formerly regarded as one species is in reality a number of races or va,rieties grouped under one name. Collected on about 70 species of wild and cultivated grasses including wheat, oats, rye, and barley, this rust is now separated into eight or more biologic forms. See p. 277. It is the most serious of the rusts, of practically world- wide distribution, and causes more damage in the Central States than any other rust except the oat black-stem-rust. It is injurious to oats, rye, and barley as well as wheat. The damage done fluctuates largely. The injury is greater to spring wheat than winter wheat. In 1916, the direct loss was placed at $110,000,000, in four states, 200,000,000 bushels in the United States, and 100,000,000 more in Canada. Total loss of the crop often results in Kentucky, Indiana, Texas, Michigan, and Ohio. In the spring or cluster-cup stage upon the barberry, swollen spots are produced upon the leaves, fruit, or young stems. These spots upon one side bear the cups in abundance and upon the other side appear as pale, circular regions which bear the small, black pycnia. Upon the wheat the rust shows first its uredinia, which come later than the uredinia of the orange-leaf-rust, and are of more brownish tinge. The sori are most common Cereals 311 upon the stems and leaf sheaths, more rare upon the leaf blade. Following this stage the black telia appear upon the stems and leaf sheaths, constituting the most conspicuous and predominating s^anptom. The damage by this disease is due to the inroads of the fungus upon the green leaf tissue, destroying the starch- producing power, diminishing the vigor of the plant, and showing its effects finally in the shrunken, shriveled grain. Since this rust usually appears late in the season, the varieties of wheat that mature early are likely to escape its attack to a greater extent than those varieties which are late in maturing. For a similar reason climatic or agronomic conditions which conduce to slow growth and late maturing of the crop favor the rust. Since the common barberry (Berberis vulgaris) and its varieties, or Mahonia is necessary to the functioning of the teliospores, these plants should not be tolerated.^^^ In Den- mark in 1903 laws enforced eradication of this barberry. Eleven years after we read '*^- ''That black rust has disappeared gradually, contemporary with the barberry bush. ''That the violent, destructive black rust attacks, which affected the whole or most of the country, mth two or three years interval, have now ceased. "That the weaker attacks which affected the grain and grasses and especially the oats in Jutland are now practically unheard of, or at least come late in the fall." Influenced by such evidence, in 1918 and 1919 the Federal authorities and those of many states, particula,rly in the Middle States and Northwest, took energetic measures to eliminate the barberry and Mahonia. Anti-barberry laws were passed in Saskatchewan, Manitoba, Canada, and many states, notably in North Dakota, Iowa, Colorado, Minnesota, Montana, Nebraska, South Dakota, Wisconsin, Michigan, lUinois. It is clear from experimental evidence that the rust does not commonly pass to the next crop on the seed, nor does it commonly overwinter in the living host plants, except 312 Diseases of Economic Plants in the extreme South. The evidence is also to the effect that such rust as does overwinter in the South does not pass to the North, but that the main source of infection in the North is from the barberry. Some durum wheats are highly resistant to rust, and recently, by selection, the Kansas Agricultural Experiment Station produced a bread wheat of the Crimean group that under Kansas conditions was highly rust-resistant. Before the rust problem can be solved by breeding resistant plants, much fundamental knowledge must be gained re- garding the biologic races of the parasites and their host ranges. Many wild grasses propagate and spread the rust and, especially if they are exposed to infection from the barberry, may bridge the way to a wheat field. Prominent among those grasses are wild barley, slender-wheat-grass, western-wheat-grass, and wild rye grasses. Obviously they should be kept down as much as possible. Orange-leaf -rust (Puccinia triiicina Eriks.). — This rust of wheat and possibly of several wild grasses is the most common and widely distributed of all rusts of the United States and is especially injurious in the southern states. It is said by Carleton that it is not only never absent from the wheat fields throughout the year, but that it is sometimes abundant even in dry seasons. Notwithstanding its preva- lence its inroads upon the crop are not usually serious, and in no case on record has it caused shriveling of the grain such as is common from the black-stem-rust. The most conspicuous character of this rust is the presence of many orange-colored sori upon the leaves, especially upon their lower surfaces. The grayish black telia are neither so prominent nor so profuse as in the black-stem-rust. Both of these rusts possess the uredinial stage, and it is difficult to distinguish them apart in this condition except by the microscope. As with the rye orange-leaf-rust, this fungus also can winter in its live uredinial mycelium and continue to bear uredinio- spores throughout the year, spending its entire existence, if Cereals 313 necessary, in this one stage upon the single species of host. While no variety of wheat is entirely proof against it, large difference is shown in this respect, some presenting high resistance, even under most adverse conditions. Early maturity is an important factor in evading rust. The following standard varieties are recommended by Carleton as possessing considerable resistance to the orange- leaf-rust in every part of the country — ''Winter wheats: Turkey, Mennonite, Pringles No. 5, Tieti, Odessa, Pringles Defiance. Spring wheats: Haynes Blue Stem, Saskatche- wan Fife. ''The following varieties seem to be resistant, but have not yet been well established as such: Theiss, Oregon Club, Sonora, Diehl Mediterranean, Fulcaster, Arnolds Hybrid, California Spring. "Some of the hardy prolific sorts not yet well known in this country, but likely to be more or less rust-resistant after thorough acclimation and selection, are — Winter wheats: Prolifero, Banatka, Red Winter, Nashi, Tangarotto, Bearded Winter, Winter Ghirka, Budapest, Crimean, Yx, Belle vue, Talavera. Spring wheats: Alsace, Spring Ghirka. "Two varieties which are quite susceptible to rust, but which usually ripen early enough to escape the worst effects of it, are: Early May and Zimmerman. "Some others not quite so well known, but probably worthy of trial as rust -escaping sorts, are — Early Baart, Allora Spring, Kathia, Roseworthy, Japanese No. 2, Yemide, Canning Downs. "These last varieties are not likely to withstand very severe winters, and are therefore best adapted to southern districts, where they may perhaps in time become accli- mated. Yemide and Kathia are probably the most hardy of the six. Canning Downs winter-killed in one trial, even in Mississippi." Yellow-stripe-rust {Puccinia glumarmn (Schum.) E. & H.). — This rust, which is serious in Europe on wheat and barley and less so on rye and several wild grasses, was found in 314 Diseases of Economic Plants Arizona in 1915 on wheat; since then, in the western United States, on barley, rye, and many wild grasses. On barley it has appeared as far east as South Dakota. Bunt, Stinking-smut ^~'^ {Tilletia Icevis Kiihn, Tilletia tritici (Bjerk.) Wint.). — Tilletia tritici causes heavy losses in the Northwest, T. Icevis in the eastern United States. Where both occur the first is known as ''low smut," the second as ''high smut" from their respective habits. This smut (for practical purposes the two may be considered as one) is readily distinguished from loose-smut by the fact that it attacks only the grain, not the inclosing chaff. The head therefore remains of much more nearly normal appearance, and it is often not until the glumes have been opened, and their contents examined, that the presence of the smut mass is detected, covered with its membrane, and resembling the wheat grain in size and shape. It may be recognized by an expert observer by its peculiar, disagreeable, penetrating odor, and by the deeper green color of the diseased heads. The smut masses are often so firm as to remain unbroken through threshing, but they may be recognized among the grains by their darker color, greater plumpness, absence of groove and germ, and finally by crushing them and lib- erating the black spores. The disease is particularly destructive, since its presence signifies not only loss of grain due to replacement by smut, but also loss in value to the good wheat, which may be largely depreciated in price by the presence of the bunt. Often bunted wheat is worthless for milling purposes and even for cattle feed. Bunt constitutes, for these reasons, one of the worst smuts in the world. Strong fanning re- moves part of the smutted grains, but troublesome wash- ing processes must be employed to remove them all, and even then the results are not entirely satisfactory. The annual loss from bunt in the United States is about 25,000,000 bu., to which should be added the frequent loss from explosion of threshing machines, estimated at $1,000,000 in two years, due to the oily combustible spores. Where low smut alone is Cereals 315 present and the heads only are harvested, the sickle-bar may be so adjusted as to leave the bunt behind. Many smut spores naturally find lodgment upon the sur- faces of healthy grains from smutted fields, or they may be carried from farm to farm upon the threshing machine. Upon planting such seed the following season these spores are ready to attack the seedling grain plant. The fungus, after gaining entrance into the seedling, grows with it throughout the season, and appears again at harvest time as spore masses within the chaff. Every grain of every head of an affected plant is usually smutted. The seedling age, like that of the oat, is the onty age sus- ceptible to smut infection. Treatment of seed wheat with formalin is usualty complete in its efficienc}^ and trifling in cost. In some sections of the Northwest, however, the soil has become so heavily infested from previous cropping and by '^smut showers" that formalin seed treatment is of but little value. In such regions early sowing and crop rotation are recommended. Loose-smut ^-^ (Ustilago tritici (Pers.) Rostr.). — Like the loose smut of barley, this smut seems to be increasing in importance. In some regions it prevails to a greater ex- tent than the bunt, causing at times a loss of more than a quarter of the crop though the loss is usually not more than 2 per cent. Loose-smut may readily be distinguished from stinking-smut of wheat by the fact that the spore masses involve the whole spikelet, which becomes dry and powdery and falls away; also by its much earlier appearance in the field, i. e., at flowering time. The spore masses are dark, ohve-black, and are produced exclusively in the spikelets. The bearded spring wheats seem to be more susceptible than the blue-stem varieties, but the smut is common on all varieties. From the studies of Maddox in Tasmania, Wakagwa in Japan, Brefeld in Germany, and others, it was known in 1896 that with the loose-smuts of wheat and barley, totally unlike the bunt of wheat and the loose-smut of oats, infection 316 Diseases of Economic Plants occurs exclusively at blossoming time; that at all other times the plants are immune. Smut spores from near-by smutted heads are blown into the wheat or barley flowers. Infection follows. The fungus then lies dormant in the grain until the seed sprouts. If the grain ripening from such infected flowers be used for seed, the fungus develops in the seedling, and an infected plant, producing smut but no grain, results, though no external symptom of the disease appears until blossoming time. Conversely, if seed result- ing from blossoms which were not infected be used, plants free from smut will be raised. The remedy in this case, therefore, lies in the use of unin- fected seed. To obtain such seed, grain must be secured from a field in which there is no loose smut, or if this is not practicable, seed grain must be raised under such conditions as will afford clean seed. It has been found that while the ordinary formalin seed- treatment is ineffective against wheat loose-smut, the hot- water treatment, in modified form, is effective, though some- what difficult of manipulation. See p. 272. Rogueing or weeding out all diseased plants from the crop that is to be used for seed, diminishes the smut largely, but does not entirely eliminate it. A practicable, effective means, which results in complete and inexpensive eradication of this smut, consists of a com- bination of the seed plat with the hot-water treatment. Flag-smut ^^^' ^-^ (Urocystis tritici Koern). — Linear, black streaks in the leaves, much like those shown in fig. 182, occur on wheat. Considerable damage is reported from Australia, India, and Japan. Flag-smut was found in Illinois in 1919. The usual formalin treatment is beneficial, though not so complete in control as with oat smut, since infection occurs, to some extent, from diseased refuse in the soil. If badly infested, the stubble should be burned to destroy as many spores as possible. Foot-rots. ^^^' ^25,554 — These diseases are characterized by a brown or black-rot on the lower part of the stem, the diseases Cereals 317 occurring in the fields in spots. They are known in many countries on wheat, oats, barley, rye, and rice, and are very destructive in Europe and Australia. The diseases in their va- rious forms have many names, among them Take-all, White- heads, Pietin. Any one of several fungi may cause foot-rot, especially when the wheat plant is weakened by adverse en- vironmental conditions. A foot-rot of wheat due to unknown cause was reported in Oregon in 1902, and one due to Hel- minthosporium in Illinois and Indiana in 1919. Burning of the stubble and crop rotation, accompanied by good drain- age, are recommended. Anthracnose {Colletotrichum cereale Manns) . — This an- thracnose seems to prevail on wheat as extensively as upon Fig. 165. — Normal wheat kernels and shriveled ker- nels due to anthracnose. After Manns. rye. The head is not destroyed, as in the case of rye, but general weakness of the plant and light, shriveled grain follows the attack. Powdery-mildew ^^^ {Erysiphe graminis DC). — The usual characters of the powdery-mildews are exhibited; a whitish, flour-like coating in irregular, circular spots upon the leaves and other plant parts. This mildew, together with the mildew of oats, rye, and barley, bears the same specific name, but upon each of these crops the form is so special- ized as not to transfer readily, if at all, to the other crop plant. Thus from the farmer's viewpoint there are prac- 318 Diseases of Economic Plants m tically four distinct kinds of mildew, although indistinguish- able to the eye. The form upon wheat grows upon all species of Triticum though some varieties show much more resistance than others. In damp, shaded spots the mildew is sometimes quite injurious, though it is rarely so over any considerable area. The conditions favor- ing the disease should be avoided. Scab ^-9 (Gihherella saubinetii (Mont.)Sacc., Fusarium). — Scab, first described in 1884 in England, seems to be quite generally distrib- uted in America, and is often the cause of large loss which, under conditions favorable to the disease, may reach from 10 to 30 per cent or higher. The loss in 1917 was estimated as about 10,000,000 bush- els. Scab appears upon the heads when about Anthracnose on wheat stems, half ripe, as yellow or pink incrustations on the spikelets, on the bases of the glumes, or covering the rachis. The affected spikelets ripen prematurely and turn yellow or brown before the normal parts mature. After ripening of the head, the diseased parts appear shrunken. The grain itself is shrunken, covered with a thick felted mycelium, and is incapable of germination. Only a few spikelets upon the head may be affected, these occupying any position — basal, terminal, or intermediate — or the whole head may be diseased. The loss consists in "V Fig. 166. Cereals 319 injury to the quality of the grain and diminution in quan- tity. Selby has shown that seedlings in the field are often killed by this disease, which is carried over in the seed. In this way as high as 5.9 per cent of death in seedlings has been caused. It has recently been shown that the fungus that causes wheat scab grows also on corn causing root-rot, and winters b a Fig. 167. — Wheat kernels: a, normal; h, shrunken and killed by- scab. After Manns. on corn refuse. Wheat planted in fields that bore infected corn becomes badly diseased. One corrective practice, there- fore, is to avoid sowing wheat on land so infested. Minor diseases Black-chaff ^^^' ^^^ {Pseudomonas translucens) . — As the wheat approaches maturity, black, sunken stripes appear lengthwise of the chaff. The rachis and leaves are also at- tacked. In severe cases the grain is shriveled. The disease was found in 15 states west of Indiana in 1917. Thorough screening and disinfection of seed by copper sulfate is ad- vised. Leptosphaeria leaf-blight ^''^ (Leptosphceria tritici (Gar.) Pass.). — The lower leaves are killed early in the season. Large loss is not usual. The Glume-blotch ^^^ 320 Diseases of Economic Plants (Septoria sps.) is common as small, dark spots upon the chaff of certain varieties of wheat. Another Septoria causes leaf- spots, especially upon the lower leaves. Eel-worms ^"' ^^^^ ^^^ (Nematodes) affecting the grain in the head have been found in several states, in some fields causing 25 per cent damage. Only clean seed should be used. Crop rotation is advised. Ergot is occasional on wheat. The Southern-blight {Sclero- tium) sometimes injures the stand in the South. FORAGE CROPS This group of crops, of high aggregate value and agricul- tural necessity, does not possess an acreage value which warrants such expensive modes of treatment as spraying. Protection against disease here must, in general, consist in modifications of agronomic methods tending to produce thriftier, more resistant plants, crop rotation to diminish the parasites, variation of time of sowing or harvesting to evade disease. Forage diseases are especially troublesome since they frequently prohibit planting of certain leguminous crops much desired in the rotation. Legumes ALFALFA Leaf-spot ^^^' '^^^ (Pseudopeziza medicaginis (Lib.) Sacc.) — No other disease of alfalfa is so universally prevalent. It constitutes the most important, in most sections the only really important, disease of this crop. Loss in vigor of the plants and loss in hay, by shedding of the leaves, result. Pammel in Iowa in 1891 estimated the loss in some fields at 50 per cent. It was first described in Europe in 1832, and noted in the United States in 1875. The leaves first show small brown to black spots, irregular or circular, which extend through the leaf and are thus visible from both sides. They are about 1-2 mm. in di- ameter, and are not sharply bordered, but shade off grad- ually into the surrounding tissue. With a hand lens very small, spore-bearing organs may be seen in the centers of the older spots, first as shiny amber-colored elevations. These elevations soon crack open and expose very small, cup-shaped sporiferous bodies, which remain surrounded by portions of the ruptured epidermis. Badly diseased leaves 321 322 Diseases of Economic Plants usually turn yellow and fall off. Spots upon the stems show the same general character as those upon the leaves. The lower leaves, and the leaves of older plants, are most subject to the leaf-spot. Plants late in the season, as of the second and third cuttings, suffer much more than earlier in the season. These crops, especially in a dry season, if allowed to stand a little too long before cutting may be badly spotted, and the loss in hay, through fallen leaves, may be 12 3 4 Fig. 168. — Four alfalfa leaf-spots due to: 1, Ascochyta; 2, Pseudope- ziza; 3, Cercospora; 4, Stagonospora. After Stewart and others. considerable. The plants are never killed by this disease, though young fields which have not yet become well estab- lished may be ruined. Its mode of dissemination is unknown, and seed treatment is useless as a preventive. The only practicable treatment is to mow down badly diseased plants with the hope that the new shoots which spring forth may overcome the disease. If the disease appears just before cutting time, the mowing should be hastened a few days in order to avoid loss from leaf shedding. Yellow leaf-blotch ^'^^ {Pyrenopeziza medicaginis Fcl., Sporonema) . — This disease is known from Vermont to the Pacific, in Europe and South America, and under certain Forage Crops 323 conditions does more damage than leaf-spot. The spot produced is deep yellow, verging to orange, and bears nu- merous orange-colored pycnidia. The fungus winters on infected leaves. Early cutting is beneficial. Wilt ^^'^ (Sclerotinia trifoliorum Eriks.). — This wilt, which in some respects resembles lettuce drop, has been noted on alfalfa and the clovers, red, white, crimson, bastard, mam- moth, and alsike, in several widely separated sections of the United States and Europe. It kills the plants, and under favorable weather conditions, the chief factor of which is a humid atmosphere, it may ex- tend from plant to plant and involve large areas in the field. Plants may show a variety of sjanptoms. Sometimes the leaves droop, and become matted together in a sodden mass at the base of the plant, and overgrown with a white cotton- like layer of mycelium, in which black sclerotia, similar to those described under lettuce, are found. At other times the stems may be the point of attack, showing dead, brown sec- tions covered with the mycelium and bearing sclerotia. Upon splitting a stem open the central part may be found filled with mycelium and with occasional sclerotia about the size of a grain of wheat. The white mycelium and black sclerotia are absolutel}' diagnostic. Under unfavorable weather conditions the disease may die out and fail to reappear, but if the weather is favorable to this fungus, the wilt may reappear year after year with increased severity, involving larger and larger areas. Stewart, French, and Wilson reported large areas where 50 per cent of the stalks were killed, though later the field recovered entirely. Where the disease is troublesome, rotation of crops and deep plowing to bury the sclerotia seem to be the only re- course. Isolated, infested areas may be cleaned out by burn- ing. Texas root-rot ^^'^^ {Ozonium). — This rot is a soil disease, which in its general characters is identical with that so disastrous upon cotton and the treatment applied to cotton 324 Diseases of Economic Plants is the only one to be recommended for alfalfa. It has been very destructive in Texas since 1892. Anthracnose ^^^ (Colletotrichum trifolii Bain) . — Alfalfa anthracnose was first mentioned in 1905 by Bain and Essary, who stated that it was prev- alent in Tennessee in 1906 and was one of the chief causes of alfalfa failures in that state. It has also been noted in destructive form in Virginia and New York. It appears as elliptical, sunken spots, 5-6 mm. long, upon the stems. The spots are gray and have dark acervuli scattered over them. Where the disease becomes aggressive, dead or withered stalks or plants are seen scattered over the field. These stalks arise from diseased crowns, which are characterized by blackening of the woody parts, below the point where the stalks are at- tacked. The only remedy seems to be the use of re- sistant varieties. Blight ^^^' ^^^ (Pseudomo- nas medicaginis Sack.). — From Colorado Paddock, in 1906, described a severe disease of alfalfa which has been noted for several successive years. It is due to bac- teria and in its early stages produces a watery, semi- transparent, yellowish to olive-green appearance along one Fig. 169. — Alfalfa crown-wart. After U. S. Department of Agri- culture. Forage Crops 325 side of the stem of the plant. The plants are at first weak, the stems light colored, later discolored or black- ened. Drops of thick fluid exude from the stems and dry upon them, giving a glistening appearance as if they were varnished. The chief damage is to the first cutting, though in subsequent years the plants may die from decay of the crown, or roots, or from loss of nutrition. Infection takes place chiefly through rifts in the epidermis due to frost, thereby affording access to wind-borne bacteria. Crown-wart ^^^ {Urophlyctis alfalfce (Lag.) Magn.). — The chief diagnostic character is the presence of numerous galls at or near the base of the stem. They vary greatly in size from that of a pea to an orange. Diseased plants have brown, dead stems, or stems that are weak and bear yellow leaves. The disease apparently originated in South America, is now widely distributed in Europe and was first noted in the United States, in California, in 1909, later in Arizona, Oregon, and Utah. Dodder "^^ {Cuscuta sps.). — Dodder, or love vine, is a parasitic, flowering plant. Its yellow, threadlike stems coil closely around the alfalfa stems, and take nourishment from them. It reproduces by seed, and the seed may readily pass with alfalfa seed unless very carefully inspected. The parasite is absolutely ruinous to the portions of the field that it infests and, since it spreads rapidly, it is a serious enemy. If dodder occurs in spots, these should be dug over or burned over before it ripens its seed, using kerosene and straw to insure heat sufficient to kill every plant, with a margin of a few feet entirely around the infested spot. Badly infested fields should be plowed up. Minor diseases Root-rot, wilt (Fusarium sp.). — The first symptom of this wilt is a yellowing of the outer leaves which gradually spreads until all of the leaves and stems become discolored, wilt, and die. This rot is said to be quite generally destrue- 1 2 3 Fig. 170. — 1, Alfalfa seed; 2, seed of large- seeded dodder; 3, seed of small-seeded dodder, natural size. After Stewart and others. Fig. 171. — Alfalfa plant and dodder. After Stewart and others. Forage Crops 327 tive in Arizona. It is a soil disease, and its general characters are those indicated on p. 26. Root-rot (Rhizoctonia crocorum DC). — Similar to the effects of Rhizoctonia upon so many other hosts, the disease consists primarily of a root-rot in which the diseased parts are coated with matted strands of the fungous mycelium, usually brownish red or violet in color, accompanied by sclerotia. The tops of plants so diseased turn yellow and die. The very aggressive fungus migrates through or over the soil to adjoining plants, and the affected spot in, the field thus enlarges, 'sometimes at a rate of 7 m. radially per year. Though long known in Europe, it has not yet appeared in many parts of America. Rhizoctonia root-rot is a typical soil disease and is kept alive in the soil by its sclerotia, which maylive at least two or three years. The general suggestions given under soil dis- eases apply. Ascochyta leaf-spot {Ascochyta medicaginis Bres.). — This leaf-spot has been noted in North Carolina, and what is probably the same disease, also in New York. The spots are irregularly circular except where they occur on the edge of the leaf, light brown in color, and bear small black dots. Cercospora leaf-spot (Cercospora medicaginis E. & E.), which appeared in Delaware in 1889, has also been noted in New York and New Jersey. The leaf-spots are nearly circu- lar, smoky brown to black, from 0.5-1 mm. in diameter, and show equally well from either surface of the leaf. They have no well-defined borders, but shade into the surrounding healthy tissue. Affected leaves turn yellow and die. It ap- pears to be disseminated on the seed. Seed disinfection is therefore recommended. A leaf-spot has also been described due to Pleosphcerulina hriosiana Poll., and others due to Septoria and Macrosporium. Downy-mildew {Peronospora trifoUorum De Bary) is a serious pest on clover in Europe and has been reported in America from Colorado, Kansas, New York, and North Carolina, though it has not yet been destructive in this 328 Diseases of Economic Plants country. The affected parts of the leaf turn yellowish gray to purple, and are frequently curled. The leaves, as seen from below, are coated with a downy fuzz, violet colored when old. Rust {Uromyces striatus Schr.) may be recognized by the typical rust sori, which are present, in this case, chiefly upon the lower sides of the leaves. The cluster-cup stage is found on Euphorbia. Anthracnose {Gloeosporium medicaginis E. & K.). — Black, rather prominent acervuli appear chiefly upon the lower surfaces of leaf-spots. The lower leaves often turn yellow and die. Seed-mold (Alternaria sp.). — Brown, dead, shriveled seeds are often noted in samples of alfalfa seed. Such seeds, if planted, develop, apparently from within, a dense black mold. Damping-off (Rhizoctonia sp. and Pythium debaryanum Hesse) is caused chiefly by the two fungi named. It has been known to affect alfalfa seedlings in the greenhouse, and it may occur to some extent in the field, especially the form caused by Rhizoctonia. Stagonospora leaf-spot (Stagonospora carpathica Baeu.) has been noted only in New York. Stewart, French and Wilson characterize this leaf-spot as follows: Unlike the Ascochyta leaf-spot, this disease attacks chiefly green leaves in the upper part of the plant. The spots are circular, 1-3 mm. in diameter, and usually light brown with a narrow border of dark brown. Each spot bears several light brown pycnidia visible on both surfaces of the leaf. Yellow-top may appear simultaneously over whole fields. The cause is unknown. White-spot is common but also is of unknown cause. CLOVER Black-mold {Phyllachora trifolii (Pers.) Fcl., Polythrin- cium). — Common red clover, crimson clover, white clover, alsike clover, and several other related plants are affected by this mold. The chief symptoms are pale spots upon the upper sides of the leaves accompanied by black dots on the lower sides. These spots at first glance so strongly resemble the Forage Crops 329 sori of the rusts as to lead the casual observer to mistake the disease for a rust. Though the disease is often of considerable damage, no treatment is known. Wilt ^^^ (Sclerotinia trifoliorum Eriks.). — The fungus caus- ing this wilt is probably identical with that of the wilt of alfalfa. It was first noted in America, in Delaware, by Chester in 1889, later in New Jersey by Halsted. The affected plants wilt and rot to the ground. White mats of myceUal threads, and later black sclerotia, are found upon or within the dead stems. Scle- rotia are especially abundant at the bases of diseased stems. Disk-like bodies, simi- lar to those described in connection with lettuce drop, develop from the sclerotium and bear spores which spread the infection. While this malady has been very destructive in Europe upon several varieties of clover, it is not yet of wide distribution in America, though it has appeared as a serious pest in a few fields. It is exceedingly difficult to eradicate when it has once gained foothold, and the European recommendation is to avoid planting the infested fields to susceptible crops. Rust (Uromyces sps.). — The clover rusts are most in- jurious to the second cutting, to which they may cause a damage of 20 or even 50 per cent if conditions favorable to the disease — damp, cool weather — obtain. These rusts, long known in Europe, were first reported in America in 1884. At the present time they are found upon red, white, crimson, and alsike clovers over a large part of the United States, though of different species, or at least different biologic races upon some of the different hosts. Fig. 172. — - Clover leaf showing spots of black-mold. Original. 330 Diseases of Economic Plants These are true rusts, and on the white clover possess all of the three stages, cluster-cup, summer or uredinial, and winter or teliospores. They attack all green parts of the plant. The most conspicuous and destructive stage is the uredinial, which is marked by profuse, circular or elongated, chestnut-brown, powdery sori. These may be few and scattered, but more often they are abundant, nearly covering the leaf, which turns black, dies, and shrivels. The rust is conveyed from plant to plant throughout the summer by spores of this stage. The teliospores or urediniospores may appear in the same or separate sori and in either event the teliospores appear later in the season. They are rec- ognized by their darker brown color. The cluster-cup stage, which is less abundant and less injurious than the other stages, may often pass unnoticed. It appears first as pale, swollen regions upon the leaf or petiole. These regions soon show the characteristic cups with orange-colored spores. The cluster- cup stage, though not known on red clover, predominates in the early spring upon many other varieties; but the uredinial stage soon gains the ascendancy over it. All three forms may be produced side by side, to some extent, throughout the summer. Hiber- nation probably occurs in two ways, by the teliospores and by the mycelium, which may remain alive in the affected parts over winter. Anthracnose ^^^ {Colletotrichum trifolii Bain). — This an- thracnose is now known on clovers and alfalfa in Tennessee, Ohio, West Virginia, Arkansas, Kentucky, and Delaware. Fig. 173. — Anthracnose on red clover stem and petiole. After Jackson. Forage Crops 331 It is first found chiefly upon the leaf stalks, later upon the stems, near the surface of the ground and just below the flower clusters, as elongated sunken spots, which result eventually in the death of the whole plant. It frequently causes great loss, and is said, by Bain, to be the most serious plant disease in Tennessee. Alsike clover is nearly immune. Hope lies in the use of resistant varieties. Anthracnose (Gloeosporium caulivorum Kirch.). — Long, brown to black, sunken spots upon stems and petioles, caus- ing death of the more distal parts, are diagnostic characters of this anthracnose, which was first reported in the United States by Sheldon in 1906, and has since been noted as serious in a number of states. Minor diseases Leaf-spot ^^^ (Pseudopeziza irifoUi (Biv-Bernh.) FcL). — • This leaf-spot much like that of alfalfa occasionally causes considerable damage. A Cercospora leaf- spot is also re- corded. Black-mold (Macros par iiim sarcinceforme Cav.) is widely distributed as the cause of concentric spots on leaf and petiole. Scab (Gibherella sauhinetii, Fiisarium) . — This parasite of cereals is also known to cause depressed, oblong spots upon clover. See wheat. Broom-rape {Orobanche minor L.) is similar to that upon tobacco. See p. 259. Root- rot (Rhizodonia) is sometimes injurious. Dodder. See alfalfa. COWPEA Wilt ^^^ (Fusarium vasinfedum Atk.). — This disease, closely like wilt of cotton, okra, and watermelon, is not com- municable from one of these plants to the other, though it is identical with the wilt of the soy bean. It first appears when the plants are about six weeks old. Up to this time they grow well and appear healthy. Scat- tered plants then begin to drop their leaves, the lower ones falling first. Growth is checked, and the stem shows a faint 332 Diseases of Economic Plants reddish brown tinge. After the leaves have fallen the stem dies and becomes covered with a light pink coating of the spores of the wilt fungus. The spread of the disease is more gradual and less conspicuous in the early part of the season, but after the peas begin to set fruit they succumb rapidly, and a field that in July gave promise of a fine crop may be entirely dead before Septem- ber without having matured a pod. The disease usually appears in spots, like the cotton wilt, and these dis- eased areas may spread until a whole field is involved. In moderate cases, or where the varieties planted are less subject to disease, only the weaker plants are killed, while the rest are dwarfed and their yield re- duced. Careful examination of the roots shows that many of the small, lateral roots are dead, small tufts of roots marking the points of infec- tion (Fig. 174) . This tufting of the rootlets is similar to that produced on cotton by the cotton-wilt fungus. In all cases the veins of the stem are brown, and the dis- ease may clearly be distinguished by cutting across the stem to observe whether the color of the wood is normal. This discoloration, which may often be seen through the translu- cent stem of the cowpea, is characteristic of this class of diseases. The name '^wilt" is somewhat misleading, since the leaves usually drop off before there is any conspicuous wilting. Fig. 174. — Roots of diseased cow- pea at left; healthy roots on the right. After Orton. Forage Crops 333 334 Diseases of Economic Plants The causal fungus is spread by the ways suggested under soil diseases. The disease is now known in most of the Southern States from North Carolina to Florida, and west to Texas, and is yearly noted in new lo- calities. Fig. 176. — Nematode galls on roots of Unknown cowpea. After Lewis. Owing to the all-important position the cowpea occupies in southern agriculture as a nitrogen crop, where the best rotation demands its frequent recurrence upon the same soil, the disease is of peculiar moment. No remedy is known except the use of the Iron cowpea or Forage Crops 335 its derivatives, the resistance of which was noted by WilHams of South Carohna in 1900. Root-knot (nematodes) is especially destructive on cow- peas. The Iron or Brabham varieties are resistant. Fig. 177. — Roots of the Iron cowpea free from nema- tode galls. After Lewis. Minor diseases Leaf-spot {Amerosporium oeconomicum E. & T.). — This disease is readily distinguished from the angular leaf-spot in that the spots are circular, are of shiny whiteness, and are studded all over with black pycnidia, smaller than a pinhole (Fig. 178). The disease is often abundant, but is usually not so serious as the angular leaf-spot. Fig. 179. — Cowpea leaflet spotted Fig. 180. — Leaflet of cowpea showing with powdery-mildew. Original. Carcospora spots. Original. Forage Crops 337 Powdery-mildew {Erysiphe pnlygoni DC). — The white spots of this mildew are strictly circular when j^oung, but as they enlarge they coalesce and cover the whole upper surface of the leaves with a white powder. The disease is very widespread, but even in the worst seasons does not do much injury. Angular leaf-spot (Cercospora cruenta Sacc). — The an- gular leaf-spots of this disease are a familiar sight in most cowpea fields. They are of various colors above, chiefly reddish, and are gray to purplish or slate-colored below. The damage is rarely very great. In some instances the at- tack may proceed to the stems, where, especially at the base, it may cause cracking and result in such lowering of the vigor of the plant as to cause shedding of leaves and failure to properly fill the pods. The loss of leaves is of course serious to the hay value of the crop. Root-rot (Thielavia) ; a Phyllosticta leaf-spot and a Sep- toria leaf-spot also occur. Streak. See sweet pea. JAPAN CLOVER (Lespedeza) Powdery-mildew {Microsphcera diffusa C. & Pk.). — The usual characters of the powdery-mildews distinguish this disease sufficiently. The injury to this valuable southern forage plant, while considerable, is never sufficient to call for treatment. SOY BEAN {Soja) Bacterial blight ^^2-534 (j>seudomonas glycineum Coerper) . — Small, angular spots, 1-2 mm. in diameter, at first water soaked, translucent, later yellow or brown and eventually brown or purplish black, occur on the leaves and pods accompanied by a bacterial exudate. The disease has been reported from Nebraska, Connecti- cut, Wisconsin, and North Carolina. It is thought to be seed-borne. Wilt. See cowpea. 338 Diseases of Economic Plants VETCH Spot (Protocoronospora nigricans A. & E.). — Upon the stems, leaves, and bracts of vetch very characteristic, long, narrow, or elliptical spots are formed, frequently with a dull purple border, and usually with a white center. When on the pods, they are obliquely situated. When old, they ap- pear as black, oblique lines. No serious damage has been reported. Downy-mildew {Peronospora vicice (Berk.) De Bary); Powdery-mildew (Erysiphe); Rust (Uromyces sps.), and Leaf-spot {Mycosphwrella) see pea, are of minor importance. Grasses Many of the diseases listed below on special grasses should perhaps be considered as general grass diseases. Thus the smut, Ustilago striceformis, is known on many genera of grasses. Grasses in general are susceptible to powdery- mildew, Phyllachora, Ergot, and rust. The biologic rela- tionships of but few of these have as yet been studied on account of their comparatively small economic significance. BARNYARD-GRASS {Panicum) Smut {Ustilago crusgalli T. & E.) is common and is readily recognized by the usual smut characters. No treatment is recommended. BLUEGRASS (Poa) Rust (Puccinia poarum Niels.). — The uredinia of this rust take even greater prominence than do the uredinia of other rusts; indeed other forms of spores are almost entirely absent in most parts of the country, throwing the burden of perpetuation of the species entirely upon the uredinial mycelium and its spores. This stage is known to be peren- nial as far north as Washington, D. C., Nebraska, and Min- nesota. The secia occur on Tussilago. Forage Crops 339 The rust is destructive, but seems to be limited to this one host. Smut. See timothy. Anthracnose. See rye. Minor diseases are caused by Uromyces poce Rab., Phyl- lachora poce (Fcl.) Sacc, and Ergot. CRABGRASS Blast (Piricularia oryzce Cav.). — This is probably iden- tical with rice blast. See p. 300. JOHNSON GRASS. See sorghum, p, 307, which has similar diseases. MILLET. See p. 295. ORCHARD -GRASS (Dadylis) Leaf-spot {Scolecotrichum graminis Fcl.). — Elliptical, dead spots may appear upon orchard-grass and on several other grasses, conspicuous upon the lower outer leaves. Death of the leaf follows sometimes, starting at the leaf tips and reaching to the base. In conditions favorable to the disease whole plants are involved. The spots, before they become confluent, are of quite characteristic appearance: large, dark brown to purplish brown. When old, they usually show at their centers spots of gray or white, and these spots may be marked with small, black specks arranged in rows lengthwise of the leaf. Black-stem-rust {Puccinia graminis Pers.). — This rust fungus may be either of the oat, orchard-grass, or Agrostis strain. Crown-Rust {Puccinia coronata Cda.). — See oats, p. 298. Anthracnose. See rye, p. 307. Rathay's disease {Bacterium rathayi (EFS.) ) ^"^^ develops with thick layers of bacteria on the surface of the plant, causing an unusual type of plant disease. 340 Diseases of Economic Plants PASPALUM Ergot ^^^ {Claviceps paspali S. & H. and C. rolfsii S. & H.). — The ergots displacing the grain are somewhat smaller than a pea, irregularly globular in outline, and pale yellow in color. Stock poisoning from pasturing on grass bearing these ergots is com- mon in the South. Mow- ing the green heads before the ergot develops will les- sen the danger. QUACKGRASS (Agropyron) Smut ( Urocystis agropyri (Preuss.) Schroet and Usti- lago) . — These smuts re- semble each other in the general appearance of the sori, though microscopi- cally the characters are quite different. Fig. 181. — ^ Ergot on Paspalum. After Beal. REDTOP (Agrostis) Black-stem-rust {Puccinia graminis agrostis Erks.). — The rust is identical with that upon wheat and oats, though infection does not readily pass from one host to the other. Smut {Ustilago striceformis (West.) Niessl). — This is the smut described under timothy. It has been known to affect 30 per cent of the plants, and to reduce the seed yield from 300 hundredweight to 70 hundredweight. Anthracnose. See rye. TALL OATGRASS Smut (Ustilago perennans Rostr.). — This smut closely resembles that of oats, though the flower parts are not so completely destroyed as in oat smut. The disease is peren- Forage Crops 341 nial in its perennial host, and smutted plants bear smut, year after year. TIMOTHY (Phleum) Smut ^^^ {Ustilago striceformis (West.) Niessl). — This smut occurs chiefly upon the leaves, more rarely upon other parts of timothy, as well as upon many species of Agrostis, Poa, Elymus, Bromus, Dactylis, Fes- tuca, in Europe, Australia, and generally throughout the United States. The spore masses form long black lines upon the leaf, and by merging and rup- turing reduce the leaf to a torn, blackened state. The affected plants are small, weak, and often fail to make seed and the hay value is thus lowered. The disease is perennial within the host. Infec- tion takes place in the blossom, resulting in a seed bearing the myce- lium of the smut. Hot- water treatment of seed (cold water 6 hours, 52° C. (123° F.) 15 minutes) gives promise of success. Rust "^^^ {Puccinia gravi- ini s phleipratensis) . — ^ , ^^ r. . n ^. ., rp,. X • 1 Fig. 182. — Son of Ustilago striaefor- This rust m^ general re- ^^^ -^ i^^^,^ ^^ ^^^^^^ ^^^^^ sembles the black-rust of Osner. 342 Diseases of Economic Plants the grains. It was first reported in 1882 and has of recent years increased rapidly. It can be transferred easily to various grasses. The secial host is not definitely known, but probably is not the barberry. The rust winters mainly in the uredinial stage. A Stripe-blight (bacteria) is recorded. Powdery-mildew is common but not serious. Anthracnose. See rye. FIBER PLANTS COTTON ^^^ Wilt ^^^ (Fusarium vasinfedum Atk.). — The cotton wilt, now widely distributed and yearly preempting more territory, is caused by a fungus that plugs the water ducts in the veins of the stem and cuts off the water supply to the parts above, always reducing the vigor of the plants and usually resulting in speedy death. Soil which produces a diseased crop one year is so infested with the causal fungus as to insure its reappearance in more extensive areas in subsequent croppings. The destructive- ness of a disease, which takes not only the crop, but in part the usefulness of the soil as well, cannot be estimated. Its injury can only be realized by those who have experienced its effects. Wilt has long been known by Southern cotton planters, both on cotton and okra, and is now prevalent in many sec- tions of Alabama, Arkansas, North Carolina, South Carolina, Georgia, Louisiana, and probably throughout the whole cotton belt. Many foreign countries also record it. Loss in Georgia was estimated as $1,000,000 annually, prior to the use of resistant varieties. The first indication of wilt appears as a yellowing of the lower leaves at the edges or between the main ribs, which portions may become almost white; later they turn brown and die. A single leaf often presents the three conditions, green (healthy), yellow (sick), and brown (dead), in bands side by side, parallel to the main ribs and radiating from the leaf stem. The dead parts may break away, leaving the leaf ragged. The upper leaves rapidly follow the course of the lower leaves. Badly affected leaves fall away, leaving only a bare stalk. In mild cases, where the disease runs its course 343 344 Diseases of Economic Plants more slowly, the intervals between the different stages are more prolonged. In light sand the disease may progress very rapidly and may consist of two stages only, the sudden wilted condition followed by speedy death. The final diagnostic symptom of the disease, however, as in the case of many other wilts, is the darkening of the affected veins, which change from the normal white to light brown or black. Though in most cases the plant dies, occasionally one revives and seems to Fig. 183. — A variety of cotton resistant to the wilt; note the complete failure of the other varieties. After Orton. outgrow the disease. In such plants relapses may follow, showing somewhat different symptoms, among them decay of the boll, and a different sequence of color changes. Rotation of crops should be practiced, the diseased plants should be pulled and burned to check the spread of the disease in the soil, and in general the recommendations given under soil diseases should be followed. Cotton follow- ing cowpeas infected with root-knot, is highly susceptible. Therefore, only cowpeas resistant to nematodes should be used in cotton rotation (Fig. 177). The ultimate solution of the question must be in the employment of resistant varieties. Fiber Plants 345 Several such have been bred by the United States Depart- ment of Agriculture. Anthracnose ^"^' ^"^ {Glomerella gossypii (South.) Edg., Colletotrichmn) . — The causal fungus of this disease was first described in 1890. It is very destructive in some localities and prevails throughout a large portion of the cotton belt of the United States and in the West Indies. The estimated loss for 1917 was 2.84 per cent or 364,000 bales. It is most conspicuous upon the bolls, where it produces unsightly ulcers, at first black, and later covered with a pink coating. The ulcers have dark brown to black, watery bor- ders and vary in diameter from a few millimeters to an area involving the entire boll. When small, the spots are reddish and slightly depressed. Attacks upon young bolls stop their growth and induce premature ripening and imperfect open- ing, or the bolls may die and decay without opening at all. In such bolls the fungus is found upon the lint and seed within. Upon the stems the fungus is limited mainly to injured parts, leaf scars, etc., and to very young, tender plants, causing damping-off. Here it is accompanied by reddening and by shrinkage in longitudinal lines. This disease upon young plants usually follows the use of dis- eased seed. Upon old stems it causes blighting of the bark, which becomes reddish brown and dies. The attack upon the leaves as upon the stems is mainl}^ limited to injured or weak parts. The seed leaves, being in a state of weakness, are especially susceptible to the fungus, which develops here with characters very similar to those on the stem and the boll. The leaves sometimes have a scalded look, assume a yellowish or leaden green color, wither and die, much as though frosted. There is evidence that the disease is largely carried from year to year in the seed and may be spread to clean seed, also, in the gin. Therefore, only seed from healthy fields and seed that has been ginned only where healthy cotton has been ginned should be used. Since the spores on the seed are short-lived, cotton seed 346 Diseases of Economic Plants three or four years old, still of satisfactory viability, is free from infection. Crops should be rotated and seed bred on isolated clean plats. Treatment with commercial sulfuric acid to remove the lint and kill the spores has given some success. Hot-water seed treatments are also beneficial against this and other cotton, seed-borne diseases. The temperature should be kept as nearly 65° C. (149° F.) as possible for fifteen minutes. Different varieties of cotton show different resistances to heat and their germination should be tested after treatment. Boll-rot "^ {Diplodia gossypina Cke.). — This is chiefly a black-rot of the bolls, which are thickly studded with pyc- nidia. These exude such quantities of black spores as to appear smutty. The entire contents of the boll also turns black. Similar effects are less common on the stem. The disease is cause of considerable loss in Louisiana. Fusarium boll-rot {Fusarium sps.). — This usually follows injury of some kind and the fungus is really a saprophyte. Other boll- rots are produced by Rhinotrichum, Volutella, Sclerotium, Olpitrichum, Botryosphaeria, and even by the gill fungus Schizophyllum. Texas root-rot ^^' ^^' ^'^^' ^^^ {Ozonium omnivorum Sh.). — The first technical description of this disease was given by Pammel in 1888. It has since been the subject of many papers, and is known to occur in very destructive form in Texas, Oklahoma, New Mexico, and Arizona, though it has not been seen east of Texas. The estimated loss from this root-rot in 1906 in Texas was about $3,000,000. Some planters regard it as a worse enemy than the boll weevil. In this disease a few of the plants may wilt and dry up in a day. Later, many plants suffer a similar fate, resulting in irregular spots of disease in the field, marked by the presence of numerous standing, dead plants. The plants succumb with marked rapidity on hot days following rain, not so rapidly in continuous dry weather. Especially after a rain, living plants surrounded by dead ones may show symptoms of the disease in the form of dense sterile mycelium upon the tap Fiber Plants 347 root. All diseased plants have diseased roots marked by injured rootlets and shrunken tap roots, accompanied by depressed spots which are at first bordered by red dis- coloration. The causal fungus is also apparent here, at first as a white mold which later turns brown or yellow and is finally accompanied by wart-like sclerotia. En- largements, from which new roots are put forth, often occur near the soil surface. Even the lint of the diseased plants is affected, the fibers being wider and larger, and the spirals fewer and more uneven, than upon healthy plants. The disease is truly of the soil, and the affected soil centers en- large yearly as in other soil diseases. It is subject to the modes of dissemination suggested on page 29. Extreme precaution should be exercised against the use, for the purpose of legume inoculation, of soil which may possibly be infested with the disease. This warning is particularly necessary in view of the fact that alfalfa is affected by the same disease, and the causal fungus is now present in many alfalfa fields. As to treatment, rotation with immune crops (see p. 23) in conjunction with deep fall plowing is recommended. To quote from Shear and Miles: '^ Rotation with immune crops at Terrell, Tex., resulted as follows: 1904, planted to cotton, about 95 per cent of which was killed by root rot; 1905, planted to corn; 1906, planted to wheat, followed by sorghum the same season; 1907, cotton again planted, with the result that, as nearly as could be estimated, less than 5 per cent of the cotton was dead at the close of the season. '^Land badly infected with the root rot was plowed seven to nine inches deep November 11, 1906, at Petty, Tex. In experiment No. 1 the deep-plowed plat showed 42.75 per cent less dead plants than the adjoining check plat which received the customary tillage. In experiment No. 2 the deep-plowed plat showed 43 per cent less dead plants than the adjoining check plat, and in both cases a much larger amount of cotton was produced on the dead plants on the 348 Diseases of Economic Plants treated plats, because these plants did not die until later than those on the untreated plats, and therefore had greater opportunity to mature their bolls." Root-knot (nematodes). — See p. 24. This knot is par- ticularly destructive on cotton, not only because of the direct injury it does, but also because root-knot greatly in- creases the susceptibility of the cotton to wilt. All means to hold the development of the nematodes in check should be employed (pp. 24-25), particularly the use of nematode- resistant varieties of cowpeas in the cotton rotation. Minor diseases Frosty-mildew {Septocylindrium areola (Atk.) P. & G.). — This leaf-spot is limited sharply by the smaller veins, and bears upon the lower surface numerous colorless spores upon colorless hyphse, thus lending a frosted appearance. Seen from above, the spots are light yellow or of a paler green than the normal leaf tissue. Widespread, though not especially destructive, it does not usually attract the attention of the planter. Leaf-blight {Mycosphcerella gossypina (Atk.) Earle, Cer- cospora) . — The fungus which causes this disease was first described from Carolina specimens in 1883, at which time its presence was recognized in South Carolina, Georgia, and Florida. The disease prevails in all cotton sections of the United States, appearing first in damp localities upon the lower leaves, and with the progress of the season, spotting all of the leaves more or less. The leaf-spots appear at first as small red dots, which finally, as they enlarge, bear brown or white centers with a characteristic red border. A copious development of dark hyphse upon the centers later gives them a blackish hue, and numerous white spores give these hyphse a white coating. The old diseased centers of the spots are brittle and frequently break away, leaving perforations. The disease is widespread but unimportant, since it is largely limited to weakened tissues, especially to spots produced by cotton mosaic. Fiber Plants 349 Angular leaf-spot ^^^' ^^^ (Pseudomonas malvacearum EFS). — This disease was first described in 1891, and is widely distributed in the cotton producing states, in Natal and the West Indies. The diseased areas appear as angular leaf-spots bounded by the veins and are of a watery ap- pearance. They may be scattered over the leaf, or they may be nearly contiguous and later become confluent, resulting in irregular dead patches. Frequently they are most numerous adjacent to the main ribs, and result in long, irregular, dead, black regions. The dead tissue is brittle and often falls away, causing holes or ragged edges. Badly affected leaves fall early and loss of 50 or 60 per cent of the leaves is not unusual. When on the boll, the spots may be a centimeter in diameter, and the seed may become infected. Seedlings from such seed are stunted and the stand poor. Cankers occur on the stems of young plants. Seed should be taken only from healthy plants. Treatment of seed with concentrated sulfuric acid to remove the lint, followed by either the mercuric chlorid or the hot-water treatments may be employed to advantage. Damping-off (Pythium debaryanum and other fungi). — Young cotton plants may suffer the characteristic soft rot of damping-off. Sore-shin {Corticium vagum, Rhizodonia) . — Primarily this is an ulcerous wound upon the stem near the ground, accompanied by reddening or browning of the leaves. If the ulcer enters deep into the stem, so as to interfere with the ascending sap, it may cause death, though the wound usually heals before the disease has progressed far. The disease is often caused by the attack of Rhizoctonia, espe- cially^ in tissues predisposed to such attack by weakness. Harrowing, to aid in drying the surface soil, to some extent prevents the attack and development of this fungus. A similar disease may also result from purely mechanical injuries caused by tools. Smut {Doassansia gossypii Lag.) occurs on the leaves in Equador and the West Indies. Rust (Kuehneola gossypii 350 Diseases of Economic Plants (Lag.) Arth.) is reported on the leaves from Florida, Cuba, Porto Rico, and British Guiana. Cluster-cup-rust {Mcidium gossypii E. & E.). — An outbreak of this disease occurred in southern Texas in 1917, causing large defoliation, with an estimated loss in yield of 20 per cent. It is commonly present in the South to a degree, but usually does not assume destruc- tive proportions. Crown-gall (Pseudomonas tumefaciens) does some injury. Mosaic, black-rust. — The first signs of this disease are yellowish spots which give the leaf a checkered appearance. The discoloration occurs first in small areas, which are roughly rectangular owing to limitation by the veins, and which are situated at points most remote from the main feed- ing veins. Usually the centers of these spots soon turn brown, and the brown part enlarges and shows a series of concentric markings. In later stages these weakened areas may be overgrown by Alternaria or other saprophytic fungi. If very dark-colored fungi grow upon these spots, they soon become black-coated and take the popular name ''black rust." Kainit, used as fertilizer, often reduces the damage from mosaic. Red leaf-blight. — This reddening, resembling autumnal coloration, occurs most frequently toward the season's end and is most common upon poor soil. It is due chiefly to lack of nourishment. Attack of mites produces a similar appearance. Shedding. — This occurs chiefly following extremes of either dry or wet weather or following a change from one ex- treme to the other. FLAX Wilt ^^^ {Fusarium lini Bolley) . — A condition of soil known as ''flax sick" has prevailed in many sections of the country to such an extent as to cause the abandonment of flax culture. This is notably true in Iowa, Minnesota, North Fiber Plants 351 and South Dakota. On such soils flax plants are attacked at any age, and die early or late according to the time and in- tensity of the infection. Man}^ of the plants are killed before they appear above the surface of the ground. Such field spots become centers of disease; they enlarge throughout the summer, and new plants sicken, wilt, and die around their margins, finally giving the entire field a spotted appearance. Young plants wilt suddenly and dry up, or decay if the weather is moist. Older, woody plants become sickly and weak, turn yellow, wilt at the top, and die slowly. Such plants are easily pulled up, owing to their decayed root system. •Many of the roots of diseased plants are dead and have a characteristic ashen-gray color. If the plant is attacked late in the season, this gray color may be limited to one side only of the taproot. In such cases the leaves and branches on the affected side are blighted. If the disease is carried with the seed into healthy soil, only a few plants may be attacked during the first year, and such plants may be very unevenly scattered throughout the field and escape notice until late in the season. If the weather favors the disease, each new area of infesta- tion may increase sufficiently to reach plants in several adjacent drill rows. These infested areas are nearly al- ways circular, and enlarge each year that flax is grown thereon. Such a spot 1-2 m. in diameter the first year may become 2-3 m. the second year. Thus only a few years are required for the disease to gain complete possession of a field. The fungus not only persists in a field not sown to flax, but the disease areas may even enlarge when no flax is present. When soil is once infested, no way is known to render it again suitable for flax culture. This is essentially a soil disease, and it is spread in the ways suggested under soil diseases, notably by soil particles, drainage water, and especially by straw of diseased flax which may get into the manure. The chief agent of dissemina- tion, however, is the seed. In threshing, the spores of the 352 Diseases of Economic Plants causal fungus, which are abundant upon the dead .straw, find lodgment upon the seed, especially if it be moist. To prevent carrying the disease to land yet uninfested, all seed should be disinfected in the following manner : Use formaldehyde at the rate of 1 pound to 40 or 45 gallons of water. Spread the seed upon a tight floor or upon a canvas and sprinkle or spray upon it a small amount of the liquid. Shovel, hoe, or rake the grain over rapidly. Repeat this spraying, shoveling, and raking until all of the seeds are evenly moistened, yet not wet enough to mat or gum to- gether. Continue to stir the grain, so that the mass may become dry as soon as possible. Avoid any excess of moisture. If flax seeds are dipped in the solution or are allowed to be- come wet enough to soften the coats so that they stick to- gether, they are liable to be considerably injured or even killed. The solution recommended is strong enough to kill all seeds if they are thoroughly saturated or are allowed to re- main damp for some hours. Less than one-half gallon of solution is required to treat one bushel of seed. It is well, also, to burn all the infested straw and to avoid too deep planting. By continued selection of seed from resistant plants Bolley has developed a variety which is resistant to the wilt. Damping-off of young plants may be caused by Alternaria or CoUetotrichum. Rust (Melampsora lint (DC.) Tul.). — Characteristic rust sori are in evidence and in the early season the leaves are yellow or orange. Later black sori appear, chiefly upon the stems. Badly affected plants turn l)rown and die earlier than plants not rusted. Large injury is not usual, though in 1904 and 1905 considerable damage was reported from North Dakota. Dodder (Cuscuta epilimmi Weihe) is similar to the dodder of legumes. See alfalfa. Fiber Plants 353 HEMP Wilt ^''' {Botryosphceria marconii (Cav.) C. & J., Dendro- phoma). — With the attack, appearing first upon the outer ends of the upper branches, the plant wilts rapidly. The foliage soon turns brown and dies. The disease seems to be a recent importation from China. TREES AND TIMBER ^'^^' ^^^ General Diseases DECAY IN LIVE TREES ^^^ ^^'^ Wood decay is caused by fungi. The mycelium penetrates through or between the wood cells, producing enzymes which soften the cells or disintegrate the middle laj^er between cells, thus destroying stability of the aggregate as by the crumbling of the plaster or the brick of a wall. Within the tree this disintegration may occur either to the heart- wood or to the sapwood, or to both. The life of a tree may be much reduced by decay of the heartwood, the main mechanical support. Decay of the sapwood further hastens death by interfering with the rise of the sap. Upon the living tree the natural protection against fun- gous invasion is the bark, consisting of cells with specially re- sistant walls; cutinized or supplied with resin, gum, or other repellents. Moreover, the dead bark is not generally nutri- tious and does not offer attractive invitation to the fungus. The protection thus constituted is normally ample; but in case of removal of this natural protection and exposure of either sapwood or heartwood, especially the latter, the path is open, and it is through wounds offering such exposure that rot in standing timber usually begins. Such rots might therefore be appropriately termed ^' wound decays." The fungi which cause these decays are, in the main, the larger fungi whose fructification is of the toadstool type (Figs. 191, 194). After the decay within is well under way the spore-bearing toadstools appear upon the surface of the diseased parts, and are quite generally recognized by lumber- men as a sign of rottenness within. 354 Trees and Timber 355 A branch, broken or sawed off, split by wind, bruised by a falling tree, gnawed by animals, pecked by birds. Fig. 184. — Fomes igniarius upon live beech tree After Atkinson. eaten by insects, or wounded in any way, may result in the exposure of heart or sapwood to the fungous spore. From this point of invasion rot spreads in every direction. When decay reaches the trunk, it spreads upward and downward 356 Diseases of Economic Plants and into all branches to which it has access. Thus trees, hollow with rot, may trace their downfall to infection of some small branch or bark wound months or even years earlier. Trees bearing the sporophores of fungi (conchs or toad- FiG. 185. — Stump of limb improperly removed. After Ind. Agr. Exp. Sta. stools) are surely infected, while the absence of su(;h evidence is no sign that a tree is healthy since the infection may be very old and the sporophore earlier in evidence may have rotted away. The fungi involved in these decays are manifold. In some cases one species of fungus grows upon many different kinds of wood. Other fungi are more particular as to their Trees and Timber 357 food supply and are found upon fewer hosts. They chiefly fall into two groups; one bearing its spores upon gills (Fig. 194); the other with its spores borne in pores. Still others bear their spores upon spines. In describing the fructification of the causal fungi for recognition pur- poses it is necessary to note especially the stalk or stiye, and the cap or pileus (Fig. 194). A cap with no stalk is ''sessile." To deter- mine the particular species of fungus that is present, it is usually necessary to examine the sporophore, and even then expert or special knowledge is needed.* The deter- mination of the species of the fungus is, how- ever, not necessary to proper treatment, since this is much the same for all. Care should be ex- ercised in felling trees to avoid injuring other trees. In forests in general, cull material and infected standing trees should be burned to prevent spore formation. Excision of the infected tissue should be practiced in case of especially valuable trees. When there are pruning-wounds, apply an antiseptic to the exposed wound to prevent the effective germination of spores upon its surface. Suitable antiseptics are tar or paint. * Useful books in such classification are given in the bibhography, Nos. 381-387. M| mm-: ^^H wm' .\; -,. ^^^^H^9P ^^Bk^'' F^ .'""'« , ^^^c<« *'• •- jHMjg mi^i.- ' %.. . , \ ^^^H H' /- '\^ r M':f: ihi / i >i\ 1 HiPv ■^, i /> H j y \N ■ ■Hi K. '^ " . .^m Fig. 186. — Wound of properly removed limb, beginning to heal over. After Ind. Agr. Exp. Sta. 358 Diseases of Economic Plants Red heart-rot, Pecky heart-rot ^^^ {Trametes pini Fr.) . — In the North this is the most destructive tree rot affecting practically all conifers, invading the heartwood, very rarely the sapwood. The wood is not wholly destroyed by the Fig. 187. — Wound of properly removed limb nicely healed After Ind. Agr. Exp. Sta. over. fungus; but series of small holes with silvery lining are noted in early stages. In spruce the color of the wood itself is changed to a light purplish gray, later to a reddish brown netted with small black lines. Small patches of white follow, which later develop into holes, arranged in series to corre- Trees and Timber 359 spond with the annual rings, and as the disease progresses result in a series of vacant spaces separated only by plates. In tamarack the decay finally destroys the plates, reducing the v/hcle wood mass to mere fiber. The sporophores may consist either of brackets or of extended sheets with shallow, pit-like pores on the under side. They are cinnamon-brown on the lower surface and much fissured and broken on the black, charcoal-like upper surface. Prevention is best effected by proper thinning, removing diseased trees, and destroying fruiting bodies. White heart-rot "^^^ (Fomes igniarius Gill.). — This is the most important and widespread of the heart-rots, and one which has the widest range of host plants. It is known in Alaska, Canada, the United States, and in South America to Patagonia, growing upon beech, aspen, birch, poplar, willow, mountain maple, sugar maple, hornbeam, white elm, butter- nut, black walnut, oaks, and hickory. It is common on fruit trees, especially when near forests. The amount of damage done by it is beyond estimation. In many cases almost the entire tmiber stand is ruined. Actual count has shown from 90 to 95 per cent of otherwise marketable trees valueless. Heart-rot, while chiefly of the heartwood, may, when started, encroach upon the sapwood, even to the youngest layers, and death may result by weakening the tree to the breaking point. The causal fungus enters through wounds, particularly broken stubs, and usually produces its sporo- phores at these points after the rot has extended a meter or so in both directions from the infection point. The first sure external sign of the disease is the presence of the sporophores, although sounding with the ax may sometimes be relied upon. The sporophores, numbering sometimes as many as twelve on a tree, are shelving, hoof-shaped bodies from 25 to 30 cm. wide. The upper surface is brown, in later stages black, hard, smooth, concentrically marked with age, finally seamed and cracked. The pores are in layers, approximately annual, and the lower surface is gray to red- brown. 360 Diseases of Economic Plants The trunk in cross-section shows rot at the center; the wood becomes soft and pulpy. The decayed region is ir- FiG. 188. — Fomes igniarius upon maple. After von Schrenk. regular in outline and bounded by narrow black layers. The tree is rarely hollow, but remains filled with the decayed wood. Young trees which bear no dead branches to admit the fungus are usually immune. Trees and Timber 361 Infective material should be burned, wounds avoided, and excision practiced in case of valuable trees. Red heart-rot, Brown-checked wood-rot ^^^' ^^^ (Polyporus sulphureus Fr.). — The conifers, also oak, chestnut, maple, walnut, butternut, alder, locust, apple, pear, cherry, and many other trees are affected. It is widely distributed, de- structive, and is especially common on shade and ornamental trees. The many-pored edible annual sporophores consist of a series of overlapping shelves, two to twenty or possibly more, with the upper surface in early stages a bright orange-red; later they are sulphur-yellow both above and below. The upper surface when bruised is brown. The sporophore is soft and fleshy when young, growing hard and brittle with age. This fungus abounds on knots and stumps. The rotted wood resembles red-brown charcoal and following decay bears concentric and radial cracks due to shrinkage. In these cracks are large sheets of fungous wefts. Diseased trees should be cut and burned to prevent infection. Piped-rot (Polyporus sps.). — The oak, chestnut, beech, and birch are susceptible to this rot, which is limited to the heart wood and is characterized by irregular, small, pocket- like patches of white fiber. These regions first appear in the wood as small, lenticular areas which increase, coalesce, and change into small pockets. These frequently become filled with a dark, red-brown mycelium. The speckled character of the wood is a distinctive mark. White-rot {Hydnum erinaceus Bull.). — Although ob- served upon many kinds of trees, oaks are chiefly affected. The rotted wood is soft and wet, with numerous holes full of light yellow floccose mycelium. The fleshy sporophores are white, 1 to 25-30 cm. in diameter, nearly spherical, and consist chiefly of immense numbers of white spines upon whose surfaces the spores are borne. Heart-rot ^'^^ {Fomes fidvus Gill.). — In Missouri and Arkansas this heart-rot is found upon birch and a number of 362 Diseases of Economic Plants other trees. The wood turns brown, and crumbles under pressure. The rot extends from 3-4 m. above and below the sporophores. These are pore-bearing, triangular in section. Fig. 189. — Polyporus sulphureus showing effect upon wood of oak tree. After von Schrenk. The upper surface is very hard and bears fine, irregular fissures parallel to the edge. When mature, the upper surface is red-brown. The pores are barely visible without a hand lens. Soft-rot ^^^ {Polyporus obtusus Berk.). — The black oaks Trees and Timber 363 {Q. marylandica and Q. velutina) are chiefly affected by this rot, which is found in Missouri, Arkansas, Iowa, Tennessee, Mississippi, New Jersey, and Maryland. Fig. 190. — • Tree weakened by Fomes fomentarius. After Atkinson. The causal fungus enters through the burrows of a wood borer. The heartwood turns light yellow, then white, and becomes brittle. Strings and sheets of white mycelium 364 Diseases of Economic Plants are found in the wood. Death results either from diminu- tion of water supply or from breaking of the trunk. Heart-rot, White wood-rot ^^^ (Fomes everhartii (E. & G.) Schr.). — This closely resembles the rot produced by Fomes igniarius. Large, rusty-brown, woody sporophores, red-brown below, grow from wounds and bear very small pores. White-rot ^^' (Poly- porus squarnosus Fr.). — In Europe this rot affects pear, oak, elm, walnut, linden, wil- low, ash, birch, beech, horse-chestnut, and maple. In America it has been reported from Minnesota. The wood becomes unusually white and bears scat- tered series of white lines. The nearly circular fruiting bodies are stalked and often at- tain a diameter of 15 cm. When young, they are soft, but later become very scaly and rough. Gill.).— This rot Fig. 191. — • Fomes fomentarius showing hoof-shaped sporophore. After Atkin- son. tough. The upper surface is Sapwood rot ^^^ (Fomes fomentarius abounds throughout the northern part of the United States, as one of the most common diseases of deciduous trees, chiefly affecting the beech and birch. Decay begins in the outer sapwood and proceeds in- ward. The wood is marked by irregular black lines, the boundaries between diseased and normal wood. When en- Trees and Timber 365 tirely rotten, the wood is soft and spongy and light yellow in color. The pore-bearing sporophores are hoof-shaped, smooth above, and concen- trically ridged and gray. Below they are red-brown. Rot {Forties ap- planatus Wallr.). — The shelving, per- ennial, pore- bear- ing sporophores are very large, woody, and grayish to brown above, and are commonly found on dead wood, as well as on live trees of poplar, beech, oak, birch, maple. Red-brown rot^^^ " (F omes pinicola Fr.). — The causal fungus is of world- wide distribution upon conifers, especially spruce, pine, fir, and hemlock. It occurs also upon birches and other deciduous trees. Entrance is made through wounds. The rotted wood is brittle, cracked, and permeated by numerous sheets of mycelium. In early stages of decay the color changes from red-brown to dark-brown, after which small, irregular, scattered white areas appear. The sporophores vary from 2.5-30 cm., averaging 10-15 cm., are bracket-shaped and lobed. The young lobes are bright red to pale yellow, old ones dark red-brown. Fig. 192. — Fomes applanatus upon trunk of dead tree. After Freeman. 366 Diseases of Economic Plants Fig. 193. — Fruiting body of Fomes pinicola upon log rotted by the fungus. After von Schrenk. Trees and Timber 367 The lower surface is pale and smooth, watery when bruised. Following is a list of the principal genera of wood-rotting fungi with the names of the trees on which they grow. Such as bear page references are discussed on the pages indicated. Fungus Armillaria, p. 370. CoUybia. Daedalea. Echinodontium. Favolus. Fistulina. Fomes, pp. 359, 364. Hydnum, p. 361. Irpex. Lentinus. Lenzites. Pholiota. Pleurotus. Pluteus. Polyporus, p. 361. Hosts Oak, apple, and trees in general. Horse-chestnut and deciduous trees gen- erally. Chestnut, maple, oak. Fir, hemlock, p. 389, spruce. Deciduous trees. Chestnut, oak. Alder, apple, arbor-vitae, ash, p. 381, as- pen, balsam, beech, birch, butternut, Cottonwood, currant, cypress, elm, fir, goose})erry, hemlock, hickory, juniper, p. 383, larch, locust, p. 391, maple, oak, olive, orange, peach, pine, plum, poplar, rose, sassafras, p. 402, spruce, syca- more, walnut, willow, and conifers and deciduous trees generally. Apple, beech, maple, oak, spruce, and deciduous trees generally. Trees generally. Aspen, birch, pine, poplar. Beech, fir, pine, poplar, spruce, and coni- fers and deciduous trees generally. Apple, oak, poplar, and trees generally. Elm, fir, maple, mulberry, pine, poplar, willow. Deciduous trees generally. Alder, apple, arbor-vitae, ash, balsam, beech, birch, p. 382, butternut, catalpa, p. 382, cedar, cherry, chestnut, elm, fir, 368 Diseases of Economic Plants Polystictus. Poria. Schizophyllum. Septobasidium. Steccherinum. Stereum. Thelephora. Trametes, p. 358. Tricholoma. Volvaria. hemlock, juniper, p. 384, larch, linden, locust, maple, oak, orange, pear, pine, poplar, Pseudotsuga, spruce, walnut, willow, and conifers and deciduous trees generally. Ash, catalpa, mountain ash, and decid- uous trees generally. Birch, catalpa, fir, hemlock, juniper, pine, spruce, and conifers and deciduous trees generally. Chestnut, horse-chestnut, mulberry, and many other trees. Apple, oak, palmetto, tupelo, etc. White cedar (ChamcBcyparis) . Birch, larch, oak, poplar, willow, and drupes and pomes. Oak and trees generally. Birch, fir, hemlock, larch, locust, pine, spruce, willow. Deciduous trees. Trees generally. Canker, gall, twig-blight. — These diseases occur upon nearly all kinds of trees. Galls are swollen parts, of the general character illustrated in Figs. 44-212. Cankers are bark diseases of varied extent (Figs. 10, 14). Twig-blight consists of death of a twig through disease (Figs. 30, 214). When occurring on valuable trees, excision or spraying may be warranted, but on forest trees, manifestly no such treat- ment is possible, and the only recourse is to adopt general sanitary measures, particularly the burning of infective material. The principal causes of these diseases with the hosts are given below. Those with page references are given more complete discussion on the pages indicated.* * References to books where descriptions of these fiingi may be found are given in the bibliography under numbers 390-394. Fungus Ascochyta. Bacteria. Botr3rtis. Cenangium. Cronartium. Cryptosporella. Cyanospora. Cytospora. Dasyscypha. Diaporthe. Diplodia. Dothidea. Dothichiza. Dothiorella. Endothia. Gymnosporan- gium. Mjrxosporium. Nectria. Trees and Timber Hosts 369 Nummularia. Phoma and Phyllosticta. Physalospora (Sphaeropsis). Pseudomonas tumefaciens. Strumella. Valsa. Spruce. Filbert, p. 389, mountain ash, mulberry, p. 393, oleander, olive, pomes, poplar, walnut, p. 404. Fir, hemlock, horse-chestnut, larch, linden, orange, pine, Prunus, spruce, sycamore. Pine. Pine, p. 395. Hazel, p. 389. Juniper. Chestnut, maple, mulberry, poplar, p. 401, willow. Hemlock, p. 390, larch, pine, spruce. Dogwood, fir. Oak, p. 394. Oak. Cottonwood, poplar, p. 401. Walnut, p. 404. Chestnut, p. 396. Cupressus, incense cedar (Libocedrus) , white cedar (Chamcecy parts), juniper. Apple, beech, conifers, oak, pear, syca- more, tulip. Alder, apple, arbor-vitse, ash, beech, birch, box elder, China berry, cherry, dogwood, elm, fir, hazel, horse-chestnut, linden, maple, mulberry, oak, pine, spruce, walnut, and conifers generally. Mountain ash, pomes. Apple, juniper, p. 385, pine. Birch, chestnut, oak, willow, fir, pomes, mulberry, elm, magnolia. Apple, chestnut, oleander, peach, pecan, poplar, quince, spruce, willow. Chestnut, oak. Alder, apple. 370 . Diseases of Economic Plants ROOT-ROTS Fungi similar to those that cause wood-rot may also at- tack the roots of trees and thus cause death either with or without any previous rotting of the trunk wood. Prominent among such diseases are the following: Shoe-string root-rot ^^^ (Armillaria mellea Vahl). — The fungus usually enters the root through wounds, and grows in Fig. 194. — Armillaria mellea attackmg a tree. After Freeman. the cambium, through which it spreads until it encircles the tree. As its growth proceeds the layers adjacent to the cambium become dry, and the top of the tree is killed by stoppage of its water supply. A characteristic accompani- ment is the profuse development of string-like, hard, black mycelial strands which permeate the soil near the base of the affected tree. From the mycelium around the base Trees and Timber 371 of the tree rise the numerous white-gilled, honey-colored sporophores, their viscid tops flecked with white; the stems swollen and with a ring (annulus) . This disease may spread for long distances through the soil by means of the fine roots and infect neighboring trees. Upon newly cleared land diseased roots of forest trees may be a source of infection to fruit trees subsequently grown thereon. The disease is common to both conifers and de- ciduous trees and has been particularly troublesome on oak, pine, chestnut, larch, sycamore, poplar, locust, hemlock, birch, alder, maple, and orchard trees. Red-rot ^^^ (Fomes annosus Fr.). — Though not very de- structive in this country, this fungus has been found on pine, spruce, fir, and other conifers, more rarely on deciduous trees, where it brings about a brown or red-rot of the root system, which ultimately results in the death of an affected tree. The fruiting bodies form small, cup-shaped shelving or irregular masses on the roots or around the base of the trunk. The fungus has also been found growing on old, dead trees. Neighboring trees generally become infected from a diseased tree, through the small fil^rous roots. Red-brown Root-rot ^^^ {Polyporus sckweinitzii Fr.). — A destructive root-rot of spruce, fir, arbor-vitse, hemlock, larch, and pine, by weakening the root or trunk, leads to the overthrow of the tree by wind. The point of attack is always the root, through the heart of which invasion is made into the trunk. This often leads to one-sided decay of the trunk's heartwood. The wood is rendered brittle, yellow, and later of cheese-like character, so that it can readily be cut cross grain when wet or reduced to a powder when dry. The pore-bearing sporophores, which appear in July or August, are from 10-35 cm. across, growing either from the roots or the trunk. If from the trunk, they are sessile; from the roots they are stalked. The fresh spore layer is rose- colored, and turns dark red if bruised. This disease is very common throughout northern for- 372 Diseases of Economic Plants ests. In Europe, where it is greatly dreaded, it is customary to prevent its spread by trenching. Groups of infected trees and trees near them may be cut to advantage to protect other trees. Other toadstool fungi that cause root-rot are Cli- FiG. 195. — Log rotted by Polyporus schweinitzii. After von Schrenk. tocybe, Tricholoma, and Septobasidium. Root-rots are also due to other fungi, chiefly the following: Ozonium Root-rot {Ozonium omnivorum Sh.). — Elm, basswood, oak, cottonwood, mesquite, china tree, mulberry, apple, and pear are affected by this rot, which has been de- scribed and discussed on page 23. Trees and Timber 373 Rhizina on fir, pine, larch, spruce, hemlock, Pseudotsuga, chestnut; Sparassis on fir, spruce, pine, larch; and Thielavia (see p. 23) on catalpa; Xylaria, see p. 53. DECAY OF DEAD TREES OR DEAD PARTS While decay of dead trees cannot be regarded strictly as a condition of disease, but rather as a post-mortem Fig, 196. — Dry-rot fungus (Merulius lacrymans) ; on the right the mycelium is visible as white strings. After Freeman. change, a word is due on account of its vast importance, involving, as it does, all structural wood. The fact that the railroads purchased 121,402,611 cross-ties in the year 1915, and larger numbers in preceding years; that the num- ber of posts in use in 1910 was approximately 4,000,000,000, 374 Diseases of Economic Plants necessitating an annual replacement of some 500,000,000 in the United States, indicates the enormous money values involved. Decay of timber is brought about by agencies similar, sometimes identical, with those causing rot in living trees, but cannot occur unless both moisture and oxygen are avail- able. Decay can be prevented by impregnating the wood with various antiseptics, as creosote or zinc chloride. ^^^' ^^^ Merely removing the bark from posts increases their length of utility. A few of the chief causes of the decay of dead wood are as follows : Dry-rot {Merulius lacrymans (Jcq.) Fr.). — One of the most common and destructive of all the rots of structural timber, it renders the wood spongy and brownish. If very moist, a profuse, superficial, pure white mycelium may develop, at first loosely, later in dense sheets or strands. The sporophores are flat, at first white, later red, and still later yellow-brown. The spore-bearing surface carries shallow pores penned between folds and wrinkles. Sap-rot ^^^ (Polyporus versicolor Fr.). — In addition to its parasitic life upon the chestnut and catalpa, this fungus grows as a saprophyte upon all kinds of deciduous woods, and is regarded as the most serious of all wood-rotting fungi which attack the dead wood of broad-leaf trees. It destroys probably 75 per cent or more of the broad-leaf species of timber used for tie purposes. Whenever such species are used for fencing, for posts or poles, or for any pur- pose where they come in contact with the soil, they are sure to be attacked sooner or later by P. versicolor. P. -per game- nus Fr is similar to P. versicolor, and also of great im- portance, appearing upon cut timber or on large wounded surfaces of standing trees, especially following fires. It is found throughout the United States on all deciduous woods. Numerous genera and species of fungi other than those mentioned above can also bring about similar changes. Trees and Timber 375 MisiXeioe ^^'^ {Phoradendron and Razoumofskya) . — While not generally considered pests, these parasites under favora- ble weather conditions may become so, especially upon trees I'iG. 197. — Trees intcstetl with mistletoe. Courtesy of the School of Botany of the University of Texas. in lawns and parks. They usually attack the smaller branches of the trees, and thus cut off the nourishment from their tips and eventually cause these portions to die. The general effect is to spoil the beauty of the tree. On forest trees they cause small diameters, reduced height, and scraggy crowns. 376 Diseases of Economic Plants To destroy mistletoe the infected branches should be cut from the trees and no berries allowed to mature, thus pre- venting dissemination of the pest by birds. Razoumofskya, the dwarf mistletoe, is represented by some eleven species in the United States, parasitic on conifers, spruce, pine, fir, hemlock, larch. Phoradendron, or the leafy mistletoe, consisting of several species is found on practically all kinds of broad-leaf trees. Witches-brooms. — The production of numerous adven- titious buds may result in the close, broomlike branching which gives rise to this common name. The condition is prevalent on many kinds of trees, particularly so on the hack- berry, which is rarely without the witches-brooms in profu- sion. They are also common on horse-chestnut, juniper, and fir. The cause of this abnormal branching is a stimulus im- parted by insects (mites), or by any one of several fungi as for example: Taphrina, Gymnosporangium, Peridermium, or the Powdery-mildews. Slime-fiux. — This is a term applied to a condition in which portions of the tree are covered by a slimy, fermenting, wet, often foamy, flow. This usually originates in sap oozing from a crack or other wound, often following surgical work, and is most in evidence when the sap flows freely. The organisms, yeast, bacteria, or their products, that induce the fermentation, may cause death of neighboring cells of the tree and result in a chronic wound, though the injury is at rn.ost little more than unsightly. Excision and disinfection niay be practiced. ' Damping-off ^^' ^^' ^^^ {Corticium, Pythium, and Fusa- rium). — Coniferous seedlings chiefly are affected. Soil disinfection by sulfuric acid, copper sulfate, zinc chlorid, or formalin, or when practicable by steam, are advised. See p. 460. Tree Surgery '^^^ ^o^, 403, 378 Ornamental, shade, and even nut and fruit trees are often of value sufficient to warrant careful surgical treatment to Trees and Timber 377 prevent further inroads by fungi already established in them. The real value of surgical treatments is somewhat problematical. The practice is of compar- atively recent popularity, and a long interval of time is necessary to determine the amount of benefit. The procedure is as fol- lows: First, all decayed, diseased, or injured wood or bark must be removed, either by severing a limb entire or by cutting out a cavity, in which case a mallet, sharp gouges, chisels, and a knife are needed. To reach all of the diseased wood it is usually necessary to en- large the opening and fre- quently to make one or more holes above or be- low the main opening, or, what is perhaps better, to cut a narrow opening of the required length. The excavation should be en- larged in all directions until only sound, unin- fected wood is left. The bottom of the cavity should be so shaped as to provide drainage. The edges of the cavity should Fig. 198. — • Detailed view of exca- vated and bolted cavities. Above cross-section of a young tree trunk showing how the new wood and bark grow into an unfilled cavity from the margin. (The line on the wood indicates the amount of ex- cavating that would be needed be- fore filling the cavity.) 3. — ■ Cross- section of a tree trunk showing the manner of using two single- headed bolts to brace a cavit}'-. After Collins. 378 Diseases of Economic Plants be undercut so that the filling will be held firmly in place, but, lest they dry out, should not be less than three- quarters of an inch thick, better an inch and a half. If there is but little undercutting, nails may be driven into the interior to hold the filling. The final cutting around the cambium should be made with a sharp knife and imme- diately followed by a coating of shellac covering the edges of the cambium, bark, and sap wood. In cavities more than two feet long, it may be necessary to reinforce the remaining wood by bolts placed every 18 to 24 inches at appropriate angles. After excision is completed, the entire inner surface Fig. 199. — Least objectionable method of an- choring guy wires to trees. After Stone, should be disinfected with creosote or carbolineum, and over this a heavy coating of tar or hot asphalt applied. The cavity may then be filled, using Portland cement and sand (1 to 3) well tamped in, the cement being put in to form blocks about 12 inches high and separated by tarred roofing paper. The face of the cement should be trimmed back to the level of the cambium. Instead of filling the cavity with cement, a mixture of dry sawdust and* asphaltum, 3 or 4 parts to 1, may be used, with the advantage of greater elasticity to meet the winds. Or the cavity may be left un- filled and simply covered with a concrete layer with ap- parently equal advantages and much saving of cement. Metal coverings of tin or zinc are sometimes used, but in general are not so desirable. Shallow cavities are merely Trees and Timber 379 excavated and disinfected and left without filling. Tree surgery should be done in mild weather, when the sap is not running actively. The necessity of surgical work can largely be avoided by early attention to wounds and especially by avoidance of wounds, and by the use of proper tree protectors and care in guying and staying branches to prevent galling or constric- tion. Leaf-spots, flower-blight. Numerous fungi cause spotting of leaves or disease of flowers of trees. These injuries are in general similar to leaf-spot, for example of celery, tomato, and other crops discussed on preceding pages. Ordinarily the injury in forests is not large, and treatment or even sanitary measures are out of the question. In the case of valuable shade, nut, fruit, or ornamental trees, or of nursery stock, spraying or dusting with fungicide is often advisable. Only the more important of the tree leaf diseases are discussed below. Following is a list of many of the fungi of leaf and flower diseases of trees with the hosts they most commonly infect. Page references are to further mention in other parts of this book.* Fungus Hosts Acantho stigma. Hemlock and conifers generally. Ascochyta. Butternut, oak, walnut. Asterina. Magnolia, oak. Cercospora. Ash, butternut, catalpa, linden, p. 391, maple, pecan, red-bud, sequoia, willow. CoUetotrichum. Magnolia. Cylindrosporium. Alder, ash, birch, elm, hackberry, locust, maple, walnut. Didymosphaeria. Catalpa. Entomosporium. Hawthorn. Fusicladium. Pecan, p. 394. * Books to aid in the study of these fungi are listed in the bibliography under numbers 390-394. 380 Diseases of Economic Plants Gloeosporium. Gnomonia. Gnomoniella. Hendersonia. Herpotrichia. Hypoderma. Keithia. Leptostroma. Leptothyrium. Lophodermium. Macrosporium. Marssonina. Microstroma. Monochagtia. Neopeckia. Peridermium. Pestalozzia. Phleospora. Phoma. Phyllosticta. Piggotia. Ramularia. Rhytisma. Rust (Uredinales) Septogloeum. Ash, beech, birch, butternut, hazel, hick- ory, horse-chestnut, Unden, maple, p. 392, oak, pecan, p. 395, sycamore, willow. Elm, p. 388. Hazel. Pine. Fir, incense cedar, larch, spruce, and conifers generally. Larch, pine, p. 397, conifers. Arbor-vitse, hemlock. Locust. Oak. Fir, juniper, larch, pine, p. 398, spruce. Catalpa, hackberry. Ash, butternut, p. 382, chestnut, p. 388, hickory, oak, poplar, p. 402, walnut, willow. Hickory, walnut, Inga. Chestnut, p. 388, oak. Pine. Fir, hemlock, pine, p. 401, spruce. Oak, spruce, and conifers generally. Elm, hackberry, sycamore, walnut. Fir, pine. Ash, beech, catalpa, p. 382, chestnut, elm, hackberry, hickory, horse-chest- nut, p. 390, linden, maple, p. 392, oak, poplar, sycamore, willow. Ash. Ash, hackberry, willow. Maple, p. 392, oak, willow. Ash, p. 381, birch, p. 382, cottonwood, fir, larch, mountain ash, osage orange, p. 394, pine, p. 395, poplar, p. 401, shadbush, willow, p. 405, Willow. Trees and Timber 381 Septoria. Alder, ash, birch, chestnut, dogwood, hackberrj^, maple, oak, pine, poplar, sweetgum, sycamore, walnut, willow. Stigmatea. Juniper, sequoia. Taphrina. Alder, birch, elm, hornbeam, horse-chest- nut, maple, oak, p. 394, poplar. Venturia. Ash, birch, mountain ash, poplar, willow. Powdery-mildews. — The general character of these dis- eases and modes of treatment are discussed on p. 122. The re- marks made above regarding leaf-spot apply to the powdery- mildews as well. The chief trees on which they occur are: alder, ash, beech, birch, butternut, catalpa, chestnut, dog- wood, elder, elm, hackberry, hickory, horse-chestnut, honey- locust, linden, locust, maple, mulberry, oak, p. 394, pecan, p. 394, poplar, shadbush, sycamore, walnut, willow. Special Hosts ASH White-rot ^^^ {Fomes fraxinophilus Peck) . — In certain localities in Missouri, Iowa, Oklahoma, Nebraska, and Kan- sas this disease affects 90 per cent of the trees. It prevails in the Mississippi valley and east to the Atlantic. The heart- wood first darkens, and later becomes soft, pulpy, and yel- lowish. The shelving, pored sporophores, 5-10 cm. long and nearly triangular in section, are numerous, chiefly near stubs or wounds, appearing soon after infection. The old, upper surface is brown or black, and very hard. Trees of any age are susceptible, but those over 10 cm. in diameter are most subject to attack. Diseased trees should be cut down, or excision practiced. Rust {Puccinia fraxinata (Lk.) Arth.). — This is a rust which may be recognized by the orange-colored cluster-cups upon the swollen parts of the leaves and petioles of nearly all species of ash. The winter condition is found upon marsh-grass, Spartina. Usually the injury is not large, but in seasons favorable to the disease defoliation may result. 382 Diseases of Economic Plants ASPEN. See poplar. BIRCH Sapwood-rot ^^^ {Polyporus betuUnus Fr.). — Several species of birch are affected by this rot, which is of wide distribution in the northern United States. The fungus en- ters the sapwood from the bark through wounds or through the lenticels, and progresses inward. When completely de- cayed the yellowish, cracked, diseased wood crumbles. Rust {Melampsoridium betulince (Schm.) Arth.). — This is much like the willow rust. See p. 405. BUCKEYE. See p. 390. BUTTERNUT Anthracnose {Gnomonia leptostyla (Fr.) C. & de Not. Marssonina). — The affected leaflets bear circular, dead, indefinitely bordered spots. The disease spreads very rapidly throughout the tree, and to other trees. Defoliation results. CATALPA Leaf-spot {Phyllostida catalpce E. & M.). — Affected leaves bear round, brown spots, often with a yellowish gray border. The spots, from 3-6 nmi. in diameter, often coalesce to form large blotches which are fragile, sometimes dropping from the leaf. Young leaves develop poorly and are deformed, while severe infection may cause complete defoliation of the tree. Soft heart-rot ""^^ (Polyporus versicolor Fr.). — The wood at the center of the tree is discolored and disintegrated, eventually becoming straw-colored and soft. The sporo- phores appear near the wound which afforded entrance. They are sessile, grouped, soft, hairy above with alternate bands of light and dark color. When old, they are tough with edges curled in. See also p. 374. Trees and Timber 383 CEDAR, RED (Juniperus) Rusts ^*^^ {Gymnosporangium sps.). — Several distinct species of the parasite occur on Juniperus, some of which produce the usual "cedar-apples/' others produce cankers or witches-brooms on the branches, or spots on the leaves. They are usually of but small significance to the cedar tree itself unless exceptionally abundant. See apple rust. Fig. 200. — "Cedar-apple," gall of the rust fungus. Original. White-rot ^^"^ {Fomes juniperinus v. Sch.). — In this dis- ease holes appear in the heartwood, extending longitudinally with a partition of sound wood between. These cavities eventually may unite to form tubes throughout the tree. The wood between one cavity and the next is not the normal red, but is somewhat browned, and the holes themselves are coated with a brilliant white lining. The cavities, partially filled with a velvety reddish-yellow mycelium, may be from 4-9 cm. long. The pore-bearing sporophore is hard and 384 Diseases of Economic Plants woody, rough above, later fissured, yellow-brown at the margin, later deep brown. The pore layer is yellow to brown. Red-rot, pecky-cedar ""^^ (Polyporus roseus Fr.). — More common than white rot, this has been observed in Missouri, "!C.JSi^ Fig. 201. — Cross-cut of cedar log showing effect of Fomes juniperinus. After von Schrenk. Arkansas, Kentucky, Tennessee, Virginia, New York, and Mississippi. The wood is full of pockets of brown, brittle wood, vary- ing from a centimeter to a meter or so in length. The sporo- Trees and Timber 385 phore, formed in the cavities under dead branches, is from 0.5-35 cm. in length by 1 cm. wide. The pore-bearing layer is flesh-colored. This and the preceding disease of the cedar taken together have been estimated to cause 60 per cent loss in some local- FiG. 202. — Longitudinal section of cedar showing effect of Fomea juniperinus. After von Schrenk. ities. Since they are caused by wound parasites, the removal of diseased trees and the destruction of sporophores is recommended. Cedar canker (Phoma sp.). — This canker is found on juniper and arbor- vitae. Injury apparently occurs only on trees under four years old. Prior to that age entire seed beds may be destroyed. 386 Diseases of Economic Plants CHESTNUT Bark-disease ^"^' ^^' ^^^ (Endothia parasitica (Murrill) A. & A.). — First noted in 1904 by Merkel in New York, this disease has spread with a rapidity and destructiveness with- out parallel in plant pathology. Its dis- tribution in 1918 is indicated in Fig. 205. The disease extended by natural agencies Fig. 203. — Chestnut-bark disease. Beattie. After Fig. 204. — Chestnut- bark disease, show- ing the sporiferous pustules. After U. S. Bur. PI. Ind. through the native chestnut forests from Maine to Vir- ginia, but shipments of nursery stock have been responsi- Trees and Timber 387 ble for its spread to distant points, to British Columbia, California, Nebraska, etc. In most of these new, distant foci, the disease has since been eradicated. In Brooklyn 16,695 trees were killed on 350 acres, and the loss in and about New York City in 1908 was placed at from $5,000,000 to $10,000,000. The total damage prior to the year 1911 is conservatively placed at $25,000,000, and may now aggregate • *?oT /nrfc riots 'I III tfVt^Al. IMffc r/o/¥S .^.-^ PMNse or eMtir«,u Fig. 205. — Distribution of chestnut blight in 1918. Office of Forest Pathology. Courtesy of the twice that amount, but this is insignificant compared with the loss that will ensue in the chestnut forests of the Appala- chians. It has already caused more damage to forest trees in America than any other fungus. The same disease has been found in China, and it is reasonably certain that it was intro- duced into the United States from the Orient some time prior to 1904. This pest is vigorously parasitic on members of the genus Castanea alone, and among the species of this genus the Japanese and Chinese varieties are highly resistant. The attack occurs upon the bark through wounds, Init twigs and leaves are not directly affected. From the point of attack 388 Diseases of Economic Plants it spreads in all directions until the diseased parts meet on the opposite side of the branch, thus girdling the twig. Dead, discolored, sunken patches with numerous yellow, orange, or reddish-brown pustules are produced; spores are extruded in greenish or yellow horns. Cankers in midsummer may en- large at the rate of a half-inch in diameter each week. The appearance of the fungus upon the trunk indicates speedy death, but if small branches are first diseased, the tree may continue to live for a few years. When once established, no means of checking this blight is known. Only preventive measures can be taken, such as destruction of diseased trees by fire, careful inspection of all nursery stock, and excision in the case of isolated trees which are considered valuable enough to justify this mode of treatment. Every general measure that has been tried has been abandoned, and at present the outlook indicates that the disease will eventually exterminate the American chestnut. To the present time $165,000 has been used by Federal appropriation and $282,500 by states, $275,000 by Pennsylvania alone, in com- bating this disease. Anthracnose, leaf-spot {Marssonina ochroleuca B. & C). — ' The characters of this disease are small bleached areas bear- ing spore pustules. It has been quite injurious to nursery varieties. Bordeaux mixture is advised. Large leaf-spot (Monochetia desmazierii Sacc). — This leaf-spot is abundant in forests, and causes much loss of vigor to the tree. It is recognized as large, 1-5 cm., circular spots with irregular concentric marking. No treatment is feasible in forests, but isolated trees can be protected by spraying. ELM Leaf-Spot ^^^ {Gnomonia ulmea (Schw.) Thm.). — The leaf spots are 1-3 mm. in diameter, and each spot is seen to con- tain a cluster of small, black, rounded elevations, the cluster Trees and Timber 389 surrounded by a Vjorder of dead tissue. Premature defolia- tion results. The disease is prevalent in all parts of the United States. FILBERT, HAZEL Blight "^^^ (Bacteria). — A serious blight, which in many respects resembles blight of pear, affects the filbert in Oregon. It occurs on buds, shoots, leaves, and as cankers on larger limbs. Black-knot ^^^ {Cryptosporella anom- ala (Peck) Sacc.). — In 1892 Halsted noted black-knot as destructive to sev- eral hundred trees in New Jersey, and in 1893 Humphry described the same disease upon hazel canes in Massachu- setts. It is characterized by numer- ous small, elliptical, warty emergences upon the bark of the diseased branches. The diseased portions are sunken, owing to the contraction of the inner bark to a mere line. The girdling pro- duced results in death of the affected canes and general injury similar to that produced by plum knot. Affected branches should be cut and burned. Fig. 206. — Elm leaf- spot. After Heald. HEMLOCK, WESTERN {Tsuga heter- ophylla) Heart-rot ^^^ (Echinodontium tiacto- rum E. & E.). — The fungus enters through wounds, chiefly branch stubs, and produces a stringy brown rot of the heart wood, which extends to all parts of the tree. A single sporophore of the fungus on the first 16-foot log of the tree trunk may be taken to indicate that the heartwood is unmarketable in both the first and second logs. The position of the largest sporophore usually indicates the region of greatest decay. 390 Diseases of Economic Plants Rust {Melampsorella elatina (A. & S.) Arth, ^cidium). — This cluster-cup fungus produces bushy distortions, ''witches' brooms," by causing profuse branching of the affected part of the tree. These abnormal branches soon lose their leaves, and cluster-cups are produced upon them. The brooms are perennial and increase in size each year, in some cases largely covering a whole tree with the brooms. In such cases the trees are stunted and may even be killed. Infection may be reduced by destroying the spore-bearing branches or by eliminating the alternate hosts, Alsine and Cerastium. Canker (Dasyscypha resinaria (C. & P.) Rehm). — Swollen cankers occur in the stems and branches, even girdling the main trunk and killing the tree. After the branch is dead the causal fungus produces spores in small disks, orange-colored within, about 4-6 mm. wide and high. HORSE-CHESTNUT, BUCKEYE Leaf-blotch ^^^ {Guignardia cesculi (Pk.) Stew., Phyllosticta) . — Unsightly spots upon the leaflets, and premature defolia- tion, render this the most conspicuous disease of this tree. The brown spots are at first circular, but as they enlarge are limited by the larger ribs, thus becoming nearly rect- angular. Pycnidia may be seen by means of a lens. This is a decided nursery pest and is also troublesome on park plantings. Lime-sulfur or Bordeaux mixture have much reduced the spotting. Dusting (sulfur, 90 parts, arsenate of lead, 10 parts) has also proved effective. LARCH Mistletoe ^^^ (Razoumofskya) . — This is the chief enemy of the western larch, attacking trees of all ages. If the trees are not killed they produce but a poor grade of timber and poor growth, and are moreover rendered liable to the at- tacks of wood-rotting fungi. All larches infected with mistletoe should be cut, whether salable or not. Trees and Timber 391 LINDEN Leaf-Spot (Cercospora microsora Sacc). — Small, circular or large, irregular, dead spots of the leaf indicate the presence of this disease. It has been reported as destructive in Mas- FiG. 207. — Mistletoe. After U. S. Bur. PL Ind. sachusetts, New Jersey, and New York. Two sprayings in Massachusetts resulted in longer retention of the foliage and lessened infection. LOCUST Yellow wood-rot ^^"^ {Fomes rimosus Berk.). — From Massachusetts to New Mexico, over the entire black locust territory, this heart-rot prevails. It is a yellow rot extending 392 Diseases of Economic Plants from the center outward in radial lines through the medullary rays; the hard flinty wood is reduced to a soft, yellow, cheesy mass, spongy when wet. The pore-bearing, shelving, hoof- shaped, sporophores develop chiefly from the burrows of the locust borers or from stubs. The young portions are light brown; older parts, dark to black and fissured. The lower side is dull red-brown. The rot ceases with the death of the tree, and posts made from diseased wood do not continue to rot. MAPLE Leaf-Spot (Phyllosticta acericola C. & E.). — A large propor- tion of the leaf may become involved, causing premature defoliation which materially lessens the value of the tree for ornament or shade. The silver maples are especially sus- ceptible, and their sale has thereby been reduced. The leaf spot was first noted in 1874 and is distributed throughout the United States. The blackish, subcircular spots as they en- large change to brown and later to dirty white in the center with black borders. Small black pycnidia may be seen in the central regions of the mature spots, which are from 10-14 mm. in diameter. Burning diseased leaves is recommended, ac- companied by use of Bordeaux mixture if economy justifies. Tar-spot (Rhytisma acerinum Fr.). — Thick, shining, irregular black spots 1-1.5 cm. across appear on the leaves in late summer and cause them to fall prematurely, thus weak- ening the tree. Considerable damage is often done to nur- sery stock. The leaves should be raked together and burned in the fall. Leaf-spot {Rhytisma pundatum Fr.). — In this leaf-spot the causal fungus forms several small, black dots upon the leaves as contrasted with the one large black blotch of the tar-spot. Anthracnose (Glceosporium apocryptum E. & E.). — Nur- sery maples have been seriously injured by this anthracnose. The tips of leaves of pruned twigs turn yellow, then blacken Trees and Timber 393 and die as though frosted. Young leaves and shoots are killed and by their death induce abnormal branching, result- ing in a compact head. The disease seems limited to young trees. Bordeaux mixture is advised — three or more sprayings. Fig. 208. — Maple tar-spot. After Heald. Thrombosis {V erticillium) . — Leaves wilt and branches die due to plugging of the veins by the fungus. Dark streaks show in the wood of affected twigs. MULBERRY Blight {Bacterium mori B. & L.). — Upon the leaf small, reddish-brown spots, pellucid when moist, are produced. 394 Diseases of Economic Plants The twigs and even entire trees are stunted and yellowed. Cankers may almost or quite girdle the stem, the diseased area becoming dark. Prune as for blight of pear. OAK Leaf-curl ^^^ {Taphrina coerulescens (D. & M.) Tul.). — Though close kin to peach curl, only a small proportion of each leaf, spots 1-2 cm. in diameter, is involved. Defoliation may result in extreme cases, and continued disease each year may cause death. Affected leaves should be burned and if the tree value warrants it sprayed as for peach curl. Powdery-mildews (Microsphcera) . — These appear late and do little harm except upon nursery stock. Flowers of sul- fur or Bordeaux mixture are useful. Twig-blight {Diplodia longispora C. & E.) does some injury. Blight. See sycamore. OSAGE ORANGE Rust (Physopella fid (Cast.) Arth.). — The sori which are scattered thickly over large areas of the lower side of the leaf are small, 0.1-0.3 mm. in diameter and are pale cinnamon-brown. This rust is known from South Carolina to Texas. PECAN 415, 416 Scab {Fusidadium effusum Wint.). — In the Southern States, particularly Florida, Louisiana, Georgia, Oklahoma, and Texas, twigs, leaves, and nuts are affected with a dark green, smoky, superficial growth. Upon leaves and petioles dead spots, distortion, and defoliation are caused. The new growth of twig is often killed, but the greatest injury is to the nuts which drop before maturity. Spraying with lime-sulfur or Bordeaux mixture, or dusting with sulfur has proved effective. Powdery-mildew (Microsphcera alni (Wallr.) Salm.). — During certain years in the South the pecan crop has been Trees and Timber 395 much injured by this mildew. It is recognized as a flour-Uke, white coating and is particularly damaging to the young nuts. Spraying with Bordeaux mixture or lime-sulfur before the fungus appears is effective. Burning of infested fall refuse is also helpful. Anthracnose (Glomerella cingulata, Gloeosporium) . — Large, light brown to reddish blotches occur on the leaves and cause them to fall. The nut hulls bear irregular, sunken, black blotches which may extend to the whole surface, and which eventually bear numerous pink acervuli. Many nuts fall prematurely. All infested refuse should be burned; a dormant spray ap- plied, another spraying given just after the buds open, and if need be, one to three additional sprayings later. Rosette. "^^^^ ^^^ — From 10 to 20 per cent of the trees in the Southeast are affected. The leaves at the branch ends are first yellow-mottled, then die. Later the twigs die back and the trees are seriously weakened. No parasite is present; the disease seems to result from deficiency of humus, food material, and moisture, and may largely be avoided by use of legumes, and by plowing under green cover crops. Die-back {Botryosphceria berengeriana de Not.). — Young twigs die and their surfaces bear numerous black perithecia. Dead wood should be pruned out and burned. Pink-mold {Cephalothecium sp.) affects the hulls, nut, and the embryo. It frequently follows scab. Brown leaf-spot (Cercospora fusca (H. & W.) Rand.), Nursery-blight (Phyllosticta caryoe Pk.), a kernel-spot {Coniothyrium) and Mistletoe do some damage. Pollen-blight (Microstroma juglandis (Ber.) Sacc. var. robus- tum Hig.) presents an interesting case of a fungus parasitic in the anthers. PINE Blister-rust ^^'^' ^-^ {Cronartium ribicola F. deW., Perider- mium) . — This rust which has done much damage in north- ern Europe on the 5-leaved or white pines, of which there are some eighteen species, entered the United States in 396 Diseases of Economic Plants quantity from Germany, between 1900 and 1909 on diseased pine seedlings, though isolated cases occurred here prior to those dates, even as early as 1892. It is now known in Maine, New Hampshire, Vermont, Massachusetts, Con- FiG. 209. — Map showing general location of pine blister infections. ^ Diseased white pines found in 1816. • Diseased currants and gooseberries found in 1916. j^ Areas of heavily infected currants and gooseberries. !:X, Centers of heavy infection where the principal efforts were made "^ to eradicate diseased plants. (Three centers of infection also exist in Wisconsin and Minnesota.) Courtesy of the Office of Forest Pathology. necticut. New York, Pennsylvania, Rhode Island, New Jersey, Kansas, Ohio, Indiana, Wisconsin, Minnesota. The alternate host is Ribes (see p. 116), some twenty-one species of which are susceptible. In the spring, sporidia from the Trees and Timber 397 Ribes telial stage of the rust may infect pines on which they fall. The first external evidence of disease appears one to several years later. The bark thickens and later pycnia develop. In the spring, secia, numerous or few, mature on the swollen bark and free their orange-colored spores. These spores falling on Ribes produce the next stage of the rust, though they cannot directly infect pine. The rust is peren- nial in the pine, the cankers enlarging year after year. Trees attacked when 3'oung, c. g., under 25 years of age, are liable to be killed. Older trees may merely lose branches or the central, top shoot. The damage to white pines is very serious. In 1909 the value of standing white pine was esti- mated at $600,000,000, the sugar pine at $120,000,000. A loss of even 1 per cent of this, which is a low estimate, is significant. In 1912 laws were enacted to prevent entry into the United States of foreign stock likely to harbor and introduce dan- gerous fungi and insect pests. Rigid Federal and state inspection is now exercised to prevent further spread of this disease. Imported Ribes and white pine must be kept well separated. If the disease is present, all Ribes should be removed from the vicinity. At the present time, $530,448 of Federal appropriations and $267,300 of state funds have been used to combat this disease. Bluing ^^^ (Ceratostomella pilifera (Fr.) Wint.). — The characteristic symptom, bluing of the sapwood, begins in August and September after the trees have been attacked by beetles. The blue color starts near the base of the tree and gradually spreads upward until the entire sapwood be- comes blue. The presence of the mycelium of the above- named fungus, which gains entrance through openings made by the beetle and is initiated by spores carried by the beetle is responsible for the color phenomenon. Blue wood is as strong as normal, green wood, is tougher, and when dry, it will last as long; but when wet, it rots rapidly. Leaf-cast (Hypoderma) . — The needles die from the tips toward the bases, becoming first reddish, then gray. Black 398 Diseases of Economic Plants lines which extend lengthwise of the leaves arfe produced by the ascus-bearing organs. Premature defoliation results. Fig. 210. — Cronartium ribicola on pine showing general aspect of disease. After Colley. Leaf-blight, twig-blight {Lophodermium hrachysporum Rostr.). — In Maine the leaf -blight has been noted as de- structive to a considerable number of small trees and in- Trees and Timber 399 juring the lower branches of large trees; serious damage, however, is not common. Damping-off {Fusarium sp.). — The general characters are those mentioned under damping-off. It is serious in Fig. 211. — Cronartium ribicola on pine show- ing sporiferous pustules. After Colley. Vermont, New York, Missouri, and probably in many other states, killing the seedlings in nurseries as soon as they ap- pear above ground. The beds should be given all ventilation possible. A top-dressing of steriHzed sand sprinkled over the beds immediately after germination resulted in 30 per cent of disease against 42 per cent in the untreated part. For dis- infection of soil, see p. 460. 400 Diseases of Economic Plants Rust (Cronartium cerebrum (Pk.) H. & L., Peridermium). — Swollen areas occur upon the branches and young stems which are gradually killed. The gall-like growth sheds a Fig. 212. ^ Gall produced by Cronartium (Perider- mium) cerebrum on pine. After Hedgcock. profusion of orange-colored spores each spring. Chiefly by its interference with the sap current the swellings bring about the death of many trees. The galls are perennial and may Trees and Timber 401 persist for many years. One stage of this rust occurs upon the oaks. Rust (C oleosporium solidaginis (Schw.) Thtim., Perider- mium). — Another species of Peridermium occurs upon leaves, producing small, sac-like, tubular outgrowths which contain the spores. Tliis is a stage of a rust which appears later in the season upon golden-rods and asters. Red-rot {Fomes pinicola Cke.). — Upon dead trees this rot begins just under the bark, usually near the tree top, often following bluing. The wood is at first wet and soggy, but soon becomes brittle, so that it crumbles readily. The cracks become filled with felted fungous threads. The sporo- phores first appear as fleshy knots, soon red, which widen to pore-bearing shelves. POPLAR, COTTONWOOD Rust {Melampsora sps.). — This is similar to willow rust. See p. 405. European-canker ^-- (Dothichiza pop- ulea S. & B.). — Species of poplar and Cottonwood in nine states show this disease. Death of the cambium re- sults, and following this numerous can- kers and dead branches render the trees unsightly. The disease was probably recently imported on the Lombardy poplar from Europe. New stock should be carefully inspected. Infected wood should be cut out and burned. Canker '^^^ {Cytospora chrysosperma (Pers.) Fr.). — This serious canker is prevalent in the southwestern United States Fig. 213. — Pine needle, bearing clus- ter-cup of rust, en- larged. After Clin- ton. 402 Diseases of Economic Plants on willow and poplar, the lesions occurring on the trunks, limbs, and twigs, with reddish pycnidia on the dead areas near the edge of the canker or over the entire dead surface. Strict inspection should guard against further spread of the disease. Resistant varieties should be used, the trees given plenty of water and protected against mechanical injury. Leaf -blight (Marssonina populi (Lib.) Sacc). — Primary infection occurs upon the leaves, resulting in small, 3-8 min., circular, black dead spots which are quite definitely bordered. As the leaves die, the patches upon the stems also turn black and die. Infection proceeds to the supporting twigs and may result in dead patches of bark upon quite large shoots. Cutting and burning infected twigs is advised. Galls {Macrophoma tumefaciens Sh.) occur on the branches. RUBBER 158 Trees and shrubs that produce rubber are subject to numerous destructive diseases, among them Cankers due to various species of Nectria, Corticium, Fusicladium, and Di- plodia; Die-back (Thyridaria) which kills the young shoots; seedling diseases due to Pestalozzia, Helminthosporium and numerous leaf fungi, and Root-rot due to Fomes, Irpex, Hymenochaete and Poria. SASSAFRAS Heart-rot {Fames rihis (Sch.) Fr.). — Spaulding in 1907 described this rot as a serious injury to sassafras in Missouri. It is also found upon stems and roots of various shrubby plants, as rose and currant. By means of a wound the attack is made upon exposed heart wood, proceeding slowly into the sap wood. The sassafras is thus immune until it reaches an age bearing heart wood. The decaying wood is abnormally light in color and slightly reddish, and the affected region is bounded by a narrow black zone. Trees sometimes die from the attack. Trees and Timber 403 The causal fungus has been reported in America from Kansas, Missouri, New York, and New Jersey. SYCAMORE Blight (Gnomonia veneta (S. & S.) Kleb.. Gloeosporium) . — First noted in 1848, this anthracnose is very widely dis- tributed on sycamore and oak from New Jersey to California and Mississippi. In extreme cases it may so weaken the trees as to cause their death. The scorched appearance of the leaves and defoliation render the trees unsightly. Just before they become full-grown the leaves give the first indication of the attack. Beginning near the veins or ribs or upon the petiole, the disease causes a stoppage of the water supply to the more distant portions of the leaf, resulting in dead areas. Dead twigs should be pruned out, and infected material col- lected and burned. Spraying with Bordeaux mixture may be practiced if the expense is war- ranted. WALNUT Anthracnose {Gnomonia lepto- styla (Fries) C. & d. Not. Mars- sonina) . — Conspicuous brown spots, 2-4 mm. in diameter, -r. oi^ w i ^ ^ • ^ ' ii 1 n 1-1 Fig. 214. — Walnut twig appear upon the leaflets, which blighted by bacteria. After soon yellow and fall. Upon the R. E. Smith. 404 Diseases of Economic Plants lower sides of the leaf spots are small, concentrically ar- ranged, black acervuli. The disease has been troublesome on black-walnut in Delaware, Iowa, Maryland, and West Virginia. Blight '^"^' '^^'* {Pseudomonas juglandis Pierce). — This blight known in 1901 only on the Pacific coast is now recorded in California, Oregon, Texas, Louisiana, Maryland, Delaware, Pennsylvania, and New York on English-walnut. Black cankered spots upon the young nuts, which fall pre- maturely, or similar spots upon the young, green shoots are characteristic. Chief damage is to the nuts, but in seasons. Fig. 215. — Bacterial blight of walnuts. After R. E. Smith. favorable to blight much of the terminal growth is killed and the succeeding crop is thereby reduced. Spraying is of questionable value. Care should be taken to select resistant trees for propagation. Melaxuma ^-^ (Dothiorella gregaria Sacc). — In this dis- ease, reported from California, black sunken cankers develop on the trunk and larger limbs, and the leaves on the smaller limbs suddenly wilt. The first indication of disease is often a black area like a blotch of tar on the gray bark. Excision and disinfection should be practiced. Other walnut troubles are : Die-back, often due to lack of or Trees and Timber 405 excess of soil moisture; Sun-burn of nuts or tree trunk; Crown-gall; Perforation, an imperfection in shell develop- ment; Root-rot; Wilt ; Yellows ; and Leaf-spot (Marssonina). WILLOW Rust {Melampsora saliciscaprce (Pers.) Wint.). — Of tree rusts this is one of the most prevalent, occurring as dusty, yellow sori upon the lower leaf surfaces. Trees are rendered unsightly by the defoliation induced. In the latter part of the season the winter sori appear as reddish brown to black, waxy or crusty spots. A similar rust is common upon cotton- wood, Balm of Gilead, poplar. Canker (Cytospora). — See poplar. ORNAMENTAL PLANTS The ornamentals give rise to problems unique in the field of plant pathology due to the fact that the number of species of plants involved is much larger than with any other group of crop plants, and moreover, because they vary greatly in value; some of them, as for example the rare orchids, have a market value higher than that of any other individual culti- vated plant; other ornamentals are of negligible commercial value. There is large diversity of financial interest; some crops are grown on a large scale by only a few individuals, others to considerable extent by nurserymen and seedmen, other crops are rarities in only a few greenhouses, while to many the flower garden in the yard has a high sentimental, though small money, value. Aside from a few standard flowers, as for example roses, violets, chrysanthemums, carnations, etc., and certain nursery stock, so few individuals are interested, or have so small a financial risk in these crops that large expenditures of public funds have not been made for investigation or control of the diseases. The result is that aside from the standard ornamental crops and a few isolated cases of other crops, the diseases have received no such complete study as has been given for example to diseases of other plants of general interest and large commercial value. Indeed in many cases knowledge is limited to a mere note of the occurrence of certain diseases or parasites, and the course of procedure is only to be inferred from knowledge of similar diseases. Flower fanciers and the commercial growers of ornamentals are able and willing and can well afford to use the best methods of treatment, and it is unfortunate that so much is lacking here concerning treatment for the specific diseases. * 406 Ornamental Plants 407 General Diseases Powdery-mildews. — For description, see p. 122. These diseases are particularly common on ornamentals un- der glass or in the open. The following Hst comprises the hosts on which they are most frequently found; Adonis, Alyssum, Anemone, Aquilegia, Begonia, Berberis, Calendula, Chrysan- themum, p. 420, Clematis, Coreopsis, Cosmos, Dahlia, p. 421, golden glow, hawthorn, honeysuckle, lilac, p. 426, larkspur, peony, phlox, p. 429, rose, p. 431, spirea, sunflower, sweet pea, p. 435, verbena, p. 436, violet, Virginian creeper. In-door or out-of-door treatments are essentially those given under rose mildew (p. 432). Cutting-bench and Seed-bed Diseases. — If plants in the cutting-bench are wounded or weak they are subject to attack by many fungi that could not injure them under normal con- ditions. The chief point in preventing inroads by these fungi is to keep the cutting-bench and seed bed in good sanitary condition, i. e., proper degree of moisture and temperature, well ventilated, and free from infestation by injurious fungi. Soil and bench, if once infested, should be disinfected (p. 460). No diseased refuse should be allowed to contaminate it. The chief trouble in the seed bed is damping-off (p. 19). Stem-rot iCoriicium). — See p. 21. Numerous plants are affected, among them: Abutilon, Acalypha, Achillea, Ageratum, Alyssum, Amarantus, Antirrhinum, Aquilegia, Asparagus, Aucuba, Bartonia, Begonia, Berberis, Calendula, Callistephus, Campanula, Celosia, Centaurea, Chrysanthe- mum, Cineraria, Coleus, Coreopsis, Cuphea, Dianthus, Eriobotrya, Erysimum, Euphorbia, Godetia, Gypsophila, Helianthus, Hibiscus, Iberis, Impatiens, Iresine, Kochia, Lathyrus, Lavatera, Ligustrum, Linaria, Linum, Lobelia, Lychnis, Lythrum, Matthiola, Paeonia, Pelargonium, Petu- nia, Phlox, Physalis, Piqueria, Platycodon, Portulaca, Potentilla, Primula, Punica, Pyrethrum, Reseda, Richardia, Ricinus, Salvia, Santolina, Schizanthus, Sedum, Seradella, Silene, Stachys, Taxus, Telanthera, Verbena, Vinca, Viola. 408 Diseases of Economic Plants Slime-mold (Physarum cinereum (Bat.) Pers.). — This mold grows as a slimy mass over any plants that are in its path, often covering an area a meter square. It later changes to the gray, dusty, sporing stage. It is not really parasitic or even injurious, but by its unsightliness, arouses the apprehen- sion of the gardener. No treatment is needed. "Root-TOt (Thielavia). See p. 23. Among the ornamentals, this disease has been noted particularly on Aralia, Begonia, Cyclamen, Dahlia, sweet pea, violet, Tropoeolum. Sooty-mold (Capnodium) may occur on almost any plant, though usually with little or no injury. It is most harmful on the camelha. (See p. 413). Other plants on which it is often seen are privet, Lonicera, palms, Cornus, yew, oleander, rhododendron. Crown-gall (Pseudomonas) . See p. 87. Crown-gall is not usually troublesome on ornamentals. It has been noted on daisy. Evonymus, honeysuckle, rose, flowering almond, chrysanthemum . Southern-blight {Sclerotium rolfsii). See p. 23. The fun- gus that causes this disease may be found on almost any host, especially in the South. Even as far north as Illinois it was destructive in gardens on Campanula, Erigeron, Dianthus, Dracocephalum, Pentstemon, Phlox, Eupatorium. Special Diseases AGAVE Anthracnose (Colletotrichum agaves Cav.). — Spots are produced on the leaves, and often cause the death of young plants. Diseased leaves should be removed and burned, and the remaining leaves sprayed. AMARANTUS (Various cultivated varieties). White-rust (Albugo) is common but not serious. See p. 164. Ornamental Plants 409 ANDROMEDA Gall {Exobasidium sps.). — See azalea. ANEMONE Rust (Cluster-cup) . — The alternate stage of the rust of drupes occurs here. Drop (Sclerotinia tuberosa Fcl.) also occurs occasionally. ASPIDISTRA Anthracnose (Colletotrichum omnivorum Hals.) is common everywhere especially upon variegated plants. ASTER, CHINA (Callistephus) Wilt ^^^' ^^"^ {Fusarium conglutinans Wall. var. callistephani' Beach.). — The wilt, mentioned as early as 1896 by Gallo- way, has since been reported from Massachusetts and Colo- rado, and is probably the most important disease of the China aster. The time of transplanting the beds and blossom- ing time are most susceptible periods, though the wilt is present to some extent at other times. The most conspicuous symptom is the sudden death of the plants. The bark of the stem is rotted at the ground line. Close observation earlier shows the leaves upon one side of the plant, particularly the lower leaves, yellowed and wilted, and the youngest leaves to be smaller than normal. The wilt- ing effect may sometimes be found first on one side only of one of the lower leaves. Plants attacked early may die, or in milder cases may survive to produce a few small blooms. If the symptoms first show at blooming time, their sequence is the same. The roots in early stages appear healthy, but the stem near the ground, in longitudinal section, shows darkening of the outer wood, local at first upon the affected side, but extending rapidly in all directions. Eventually the dis- coloration extends into the bark, which rots away. 410 Diseases of Economic Plants In the seed bed the same disease may occur as damping- off. See p. 19. It seems that original infection always oc- curs in the seed bed, never in the open. Plants started in the open are not susceptible. If it is necessary to start them under glass, too thick sowing should be avoided, and they should be ventilated thoroughly. Soil that is known to be in- fested should not be used. The disease may be pre- vented by avoidance of the conditions that favor damp- ing-off. Yellows. ^-^ — Growth is spindling and the shoots and leaves are yellow, but no death of affected parts occurs. In badly diseased plants no flowers, or only rudiments of such, develop upon the sick shoots. In other cases the flowers turn greenish-yellow, wholly or in part, with malformed floral parts producing little or no seed. No parasites are present and the cause of the condition is unknown, but the striking similarity to peach yellows is obvious. The same disease affects the marguerite. Rust {Coleosporium solidaginis (Schw.) Thuem.). — Orange-red sori, waxy in consistency, are produced in great numbers upon the leaves, which when badly affected curl, die, and thus bring about the death of the plant. Stem- rot {Corticium). — See p. 21. Fig. 216. — Rust on barberry. After Stakman. Ornamental Plants 411 AZALEA Leaf-spot (Septoria) is common on the leaves. Gall {Exohasidium sps.). — Leaves, flowers, or shoots are en- larged and distorted. Diseased parts should be cut and burned and the plant sprayed with Bordeaux mixture. BALM, SILVER Rust (Puccinia men- thce Pers.). — Some thirty species of the mint family, including peppermint, thyme, catnip, monarda, are affected by this rust. It is recognized by its sori, which are at first cinnamon-colored, later chestnut-brown. Badly diseased leaves curl and die. Infested refuse should be burned. BAMBOO Smut ( Usttlago shir- aiana Hem.). — The short branches still covered by the leaf sheaths are attacked. f %>- Tig. 217. — Barberry rust enlarged. After Stakman. Witches-brooms are frequently formed. It has been found in this country on two species of bamboo. Diseased plants should be burned. BARBERRY Rust (Puccinia graminis, .^cidium). — This is of chief interest on account of the damage the other stages of the 412 Diseases of Economic Plants rust causes to cereals. Rusts from many grasses pass to the common barberry though not to the Japanese bar- berry. See p. 277. Wilt {Verticillium alboatrum R. & B.) affects the Japanese barberry. The fohage turns yellow or red; the sapwood is streaked with dark lines; ultimately the wood turns black. Frequently the disease is severe. BEGONIA Eel-worms in the leaves cause translucent watery spots. Powdery-mildew does some harm. BLETIA Anthracnose (Colletotrichum hletice Hals.). — The leaves of this orchid are frequently disfigured by very dark, almost black spots. In late stages the dead tissue falls away, leaving merely shreds of veins traversing the place of disease. The tips of the leaves are often frayed. Volutella rot (Volutella concentrica Hals.). — Numerous lemon-colored acervuli surrounded by concentric bluish rings render these spots different from those above described. CALLA Soft-rot ''-^ (Bacillus carotovorus Jones). — A large annual loss and frequently the abandonment of calla growing is due to this disease, which is known throughout the United States. The affected plants rot off near the soil surface, and the rot progresses from this point up into the leaves or down into the corm. Usually the rot first shows at the top of the corm, but in some instances it is seen first at the edge of a petiole, or on the corm below ground. In section the diseased portion is brown, soft, and watery. Leaves whose bases are diseased become pale at the edges, then brown. Similar changes occur in spots on the leaf, and the whole leaf eventually dies, or the rot may progress so rapidly that the leaf falls before losing its green color. The Ornamental Plants 413 flower or its stalk are similarly diseased. Through the corm the roots are reached. Here the skin is unaffected and re- mains as a parchment-like tube filled with the creamy residue of decay. Rot of the bulb may be arrested by unfavorable conditions and show only as dark sunken spots. The course of the disease extends from a few days to several weeks, or the disease may lie dormant for months, even from season to season. Such cases of dormant disease carry the infestation to the succeeding crop and in commercial corms from country to country. The rot spreads rapidly from plant to plant by way of the diseased roots and through the soil itself. The causal bacillus remains in the soil and may attack healthy corms planted therein at later periods. No known treatment of diseased plants is practicable. Infestation of soil may be prevented by careful inspection of all corms so as to avoid diseased ones. It is best to test commercial corms in pots to be assured of their healthful- ness before putting them in the beds. All soil from badly infested beds should be disinfected or removed and fresh soil supplied. Leaf-spot {Phyllosficta richardiw Hals.). — Blighted leaves bear large ashen spots upon which are numerous minute dark pycnidia. Another Leaf-spot due to Cercospora richardicecola Atk. was first mentioned by Atkinson in 1891 as occurring in Ala- bama. The edges of the leaves turn black in circular spots. CAMELLIA Sooty-mold {Capnodium sp.). — The sooty -mold is perhaps more injurious on this plant than on any other ornamental, not as an actual disease but by injury to salability of the foli- age. Leaf-spot {Pestalozzia guepini Desm.) is common. CANNA Rust {Puccinia cannce (Wint.) P. Henn.). — This true rust is common and injurious in the warmer climates but is rare in the more temperate regions. 414 Diseases of Economic Plants CARNATION Rust ^"^' "^^^ {Urornyces caryophyllinus (Sch.) Wint.). — The carnation rust was first described in 1789 in Germany and was noted in the United States by Arthur in 1891, evidently a recent importation. It rapidly became wide- spread through sale of infected plants and cuttings and was soon present in almost all greenhouses. Though widely known in Europe, it did not seem to be especially destructive there; but upon entrance into America its character changed to that of an aggressive pest, and ruin was brought to the beds in many greenhouses. The entire contents of large houses valued at thousands of dollars was in many instances utterly lost. After a short period of extreme destructiveness, which was at its height about 1893, the vigor of the attack waned, until to-day the pest does only a small fraction of damage as compared with that of the early years of its inva- sion, though it still causes one of the serious carnation diseases. The rust is easily recognized by the sori filled with powdery, brown spores. The sori, at first covered by the white epider- mis, are 1-2 mm. in diameter, round or elongated in the direction of the length of the stem or leaf. When very numerous, the affected part is slightly bleached or yellowed and appears swollen, owing to the much-ruptured epidermis. The mycelium of the causal fungus is usually general through- out affected plants, but may, in case of new infection, be limited to the immediate region of the sorus. There is much difference in varietal resistance, a fact that should receive due weight in the selection of varieties for culture. Cuttings should never be taken from diseased stock. If there is doubt as to the presence of superficial spores, it is well to dip the cuttings in potassium sulfid, one ounce to one gallon. A weekly protective spray of copper sul- fate, one pound to twenty-five gallons, throughout the life of the plant is also recommended. The leaves should be Ornamental Plants 415 kept as free from moisture as possible by free ventilation, and still better by subirrigation. Fumigation of the houses in the fall before the intro- duction of the plants serves to lessen infection from old spores. Rust sori are occasionally the seat of attack b}^ a Fu- sarium,^^^ the result being a leaf-spot a centimeter or more in diameter. Leaf-spot {Septoria dianthi Desm.). — The spots of this disease — usualh^ upon the leaves, sometimes upon the stems — are circular or oblong, blanched or pinkish, and purple bordered. Numerous small, black pycnidia lie in the central region. The disease is especially abundant upon the lower portion of the leaves and the sheaths. The diseased part often becomes contracted, which results in bending and curling of the leaves. Surface watering of the plants or humid atmosphere tend to increase the trouble. Another Leaf-spot is due to Vermicularia subeffigurata Schw. — The bases of the leaves or the stems are usually the points of attack. Black spore-bearing bodies appear in abundance. Spraying with ammoniacal copper carbonate has given good results. Altemariose "'^^ (Alternaria dianthi S. & H.). — This leaf and stem disease has been reported as quite troublesome in Connecticut, Pennsylvania, District of Columbia, North Carolina, Missouri, and elsewhere. It consists of spots mostly upon the leaves, sometimes upon the stems, especially at the nodes. These are strikingly characteristic, of ashen whiteness, with the centers occupied by a scanty, to profuse, black fungous growth. The diseased spot is dry, somewhat shrunken, thinner than healthy portions of the leaf, approx- imately circular, though often somewhat elongated in the direction of the longitudinal axis of the leaf. When at the node, the disease usually involves the bases of both of the leaves, as well as the stem between them. As these nodal spots age, the disease penetrates through the stem, killing its tissue, which shrinks somewhat and becomes soft 416 Diseases of Economic Plants and disintegrated, resulting in the death of the more distal portions of the plant. A striking feature is the tendency of this disease to infect to a large degree one variety, the Mrs. Thomas W. Lawson, to the exemption of others. Stem-rot, wilt ^^" {Fusarium sp.). — Described in 1897 by Sturgis, this rot occurs chiefly upon the stems and larger branches, discoloring the wood and killing the bark, but rarely causing soft rot. The diseased plant dies gradually with yellowing and drying of the foliage, much as though due to insufficient water supply. When practicable, beds should be disinfected, and new uninfected stock introduced. The disease when first intro- duced upon a few plants can be stopped by the immediate removal and destruction by fire of the diseased plants. Leaf-mold. {Heterosporium echinulatum (Berk.) Cke.). — Circular spots, 1-4 mm. in diameter, bearing more or less concentric zones of dark mold, appear upon the leaves, espe- cially the younger ones, also upon the stems and sometimes upon the calyx. Mold upon the calyx results in deformed flower parts. In some instances the whole top of a plant becomes moldy. Infested refuse and leaves should be burned and Bordeaux mixture employed as a spray. Bacterial-spot ^^^' ^^^ (Pseudomonas woodsii (EFS)). — • The spots of the leaves and stems are small, usually sur- rounded by a narrow water-soaked area, while the center is commonly slightly brown. As the spots grow larger they resemble Septoria spots with the exception of the water- soaked margin. Later they dry and collapse. Badly diseased leaves wither. In some cases nearly all the leaves on many of the stems are so badly diseased as to be hopeless. This trouble can be checked by removing and burning all diseased leaves, then spraying with formalin, 1 part to 500. A somewhat similar spot caused by Aphides is known as Stigmonose. Gray-mold {Botrytis sp.). — A gray-mold similar to that Ornamental Plants 417 upon lettuce sometimes attacks the carnation bud, rotting it before it opens. Infested refuse should be burned and thorough ventilation provided. Bud-rot ^^'^ {Sporotrichum aiithophilurri Peck). — In this malady some buds never open, others fail to expand to perfect flowers, still others deviate only slightly from the normal. Badly affected flowers, if not picked, wither and turn brown — first the petals, then the sepals. All parts of the flower within the calyx are eventually affected with a rot, and in some cases, though not always, hyphse of the causal fungus may be seen with the naked eye. Mites are usually present, but they are not responsible for the disease. Neglect is among the prominent predisposing causes, especially the presence of too much water in the soil or air, and the accumulation of debris, leaves, trimmings, and other organic matter on the benches. The disease may cause considerable damage; thus a daily loss of from $1.50 to $2 is recorded in one small house. Since the buds only are affected, not the plants themselves, no permanent injury is done, and clean culture, destruction of all refuse which might harbor the fungus, maintenance of moisture at the minimum, and the picking and burning of all infected buds will soon bring relief. Rot (Volutella dianthi Atk.). — The affected parts are pale and studded with minute, black acervuli. This disease is of greatest injury in the cutting bench. Stem-rot ^-^ (Corticium vagum) . — Plants suddenly wilt, dry, and die, while the outer portion of the stem becomes soft and rotten. Sclerotia as described in connection with potato stem-rot are present. For further discussion of stem-rot, see p. 21. High growing temperatures and excess of mois- ture should be avoided. Infested soil can be disinfected by steam. Yellows. — Irregular, sunken spots occur. The cause is unknown. 418 Diseases of Economic Plants CHRYSANTHEMUM Leaf -spot ^^'^ {Septoria chrysanthernella Cav.). — Large brown to black blotches, often irregularly circular and of indefinite border, appear upon the leaves. These enlarge and coalesce to involve the whole leaf, which withers, dies, and falls away. The lower leaves are first affected, but in later stages all the leaves of the plant may be badly spotted, and practically complete defoliation may result. Cuttings from infected stock should be avoided. All diseased foliage should be picked, collected, and burned, and the remaining foliage should be sprayed with Bordeaux mixture with addition of soap sufficient to form a suds to increase its adhesive power. Five or six sprayings during the season are usually sufficient. Leaf-spot (Phyllostida chrysanthemi E. & D.). — This disease, first described in 1893, is very similar to the above, ex- cept that the spots are more regularly circular, are purplish brown, and have a distinct border. Pycnidia which may often be seen with the naked eye are present. Wilt (Fusarium sp.) occurs occasionally. Rust ^^^ {Puccinia chrysan- themi Roze) . — Apparently a na- tive of Japan, the rust was introduced into England (1895) and Europe through commercial agencies, and similarly into the Fig. 218. - Chrysanthemum jj^^^^^ ^^^^ ^^^^^^ -^ ^^^ gj.g^ leaf showmg rust son. Ong- ^^^^^ .^ ^^^^ .^ Massachusetts. It was rapidly spread throughout this country by diseased stock, and is now known in nearly all localities where the chrysanthemum is cultivated. The Ornamental Plants 419 loss occasioned by the diminution in vigor of the plant and consequent imperfection of bloom is large. The sori, 2-3 mm. in diameter, which are diagnostic, first appear as small blisters covered by the epidermis. The rupture of this covering dis- closes a dark brown mass of spores. The sori are usually numerous upon the lower leaf surface, and the spores form dusty coatings upon the leaves. Badly affected leaves curl; shrivel, and die. The plants are dwarfed and fail to produce flowers of value. All new stock introduced to the houses should be care- fully inspected and all dis- eased stock destroyed by fire. New stock should be isolated and watched for a month or more to be sure that no rust develops. If disease ap- pears, all affected leaves should be picked and burned with precautions to avoid scattering the spores. If the rust continues to appear, all parts above ground must be destroyed by fire at the end of the season, and plants for the next year raised in un- contaminated soil and house. Ray-blight"*^'' {Ascochyta chrysanthemi Stev.). — In this disease, described by Stevens as doing considerable damage in North Carolina, the ray flowers are blighted, resulting in imperfect opening of the buds. Thorough spraying with Bordeaux mixture from the beginning of the season until Fig. 219. — Chrysanthemum blossom distorted with ray- blight. Original. 420 Diseases of Economic Plants blossoming, accompanied by destruction of infested refuse, has proved a satisfactory treatment. Powdery-Tnildev/ {Erysiphe cichoracearum DC, Oidium). — This mildew occurs as white, flour-like spots upon the green parts of the plant. It is not often serious, but if it should become so, can readily be controlled by the means suggested for rose mildew. Leaf-spot (Cylindrosporium chrysanthemi E. & D.).^ — First described in 1893, this closely resembles Septoria spot, though it develops somewhat more rapidly and is conse- quently more injurious. Often the leaves die and flowers fail to form. Treatment is the same as for Septoria leaf- spot. Gall (Pseudomonas tumefaciens) . — Galls upon the stems of this plant have been proved by Smith and Townsend to be due to Pseudomonas. Treatment has not yet been discussed. CINERARIA Rust {Coleosporium senecionis (Schum.) Fr.) is occa- sionally serious. CLEMATIS Stem-rot ''^^' '^'^^ {Ascochyta clematidina (Thuem.) Gloy.). — Plants affected with this disease were first noted in 1883. A leaf spot is produced; the petioles are affected and the fungus grows down to, and girdles the stem at the node. Diseased leaves should be removed and the plant sprayed. Leaf-spot (Cylindrosporium clematidis E. & E.). — This occurs on clematis in propagating houses causing the loss of the lower leaves. COLOCASIA Rot/^^ — Several kinds of rot occur on the cormels, prominent among these are the Java black-rot (Diplodia sps.), Powdery gray-rot (Fusariuni) , Southern blight (Sclerotium rolfsii) ,"*Sof t-rot (Bacillus carotovorus) . Ornamental Plants 421 COSMOS Stem-blight ^^^ {Phomopsis stewartii Pk.). — The first indication of disease is seen in brown discoloration of the stem or branches, the attack often, though not always, occurring at a wound. The diseased branches at the point of attack are weak and frequently break off. Minute pycnidia are present in the diseased parts. The disease appears only on mature plants and is very destructive. CYCLAMEN Leaf-spot {Phoma cydamenw Hal.). — A disease of the foliage which sometimes causes almost entire loss of the crop is marked by large, dark, irregularly shaped spots upon the leaf. These spots later dry, turn lighter in color, and show a series of concentric light and dark bands, at the same time becoming brittle and often breaking away. Dis- eased leaves should be burned and the plants sprayed with Bordeaux mixture or ammoniacal copper carbonate. Several fungi as Ascochyta, Botrytis, Phyllosticta, Ramularia, Sep- toria, cause leaf-spots. Anthracnose {Glomerella cingulata var. cyclaminis P. & C). — The spots on the leaves are circular, watery, with definite borders. Black, hairy acervuli are often present in great numbers. Nematodes and Thielavia occur on the roots. DAHLIA Powdery-mildew (Erysiphe communis Wallr, Oidium). — This powdery-mildew is quite common, affecting particularly the lower leaves late in the season. Blight {Phoma dahlice Berk.). — The stems of the flowers are the chief seats of attack. The flowers are small and are often dropped before opening. Root-rot (Botrytis) occurs in storage as a wet soft rot. Wilt (Verticilliutn dahlioe Kleb.). — Cf. p. 180. 422 Diseases of Economic Plants DAISY Crown-gall (Pseudomonas) does but slight injury. DRACAENA Leaf-Spot (Phyllosticta niaculicola Hal.). — This may be recognized as small, brown, somewhat angular spots on the leaves, each spot surrounded by a rather wide yellow border. Minute pycnidia are present. FERNS Blight (Phyllosticta pteridis Hal.). — The tender growing tips of ferns are subject to blight, and blighted spots may also occur lower upon the leaf. The brown dead tips and leaf spots bear minute pycnidia. Blighted parts should be cut away and burned and the remaining foliage sprayed with Bordeaux mixture. The disease is strictly local, and close attention will stop its spread, even after it has considerable foothold. Numerous other fungi are recorded on various species of ferns, chiefly causing leaf-spots. Prothallium-blight (Completoria complens Lohde) . — Upon sporelings (prothallia of Aspidium and Pteris) this disease is first shown by a yellow or yellow-brown color, as seen in mass. Under a hand lens the abnormal color is seen as spots, varying from green to yellowish-brown and later to black. In later stages disintegration of the affected cells gives the prothallia a ragged appearance. GERANIUM (Pelargonium) Gray-mold (Botrytis sp.). — Frequently this mold appears on old blossoms, thence spreads to buds and even to leaves. Proper sanitation, destruction of all refuse, and attention to ventilation usually prevents this mold. Bacterial leaf-spot (Pseudomonas erodii Lew.). — The spots are watery, brown when old. The affected leaves fall. Ornamental Plants 423 GLADIOLUS Hard-rot ^''^ {Septoria gladioli Pass.). — Leaves are af- fected with brown or purplish, irregularly circular spots having gray centers and bearing numerous, black pycnidia. On the corms lesions appear as water-soaked, dark spots which later become sunken and black. The diseased tissue is extremely hard. Spraying of seedlings is effective, but a simpler method is to plant the seed in soil that has not borne Gladioli, and to bring to it no infective material. HAWTHORN Rust {Gymnosporangium sps.). — The rust, similar to that of the apple, is often abundant. HEPATICA Rust (Transchelia, ^cidium). — This is perennial in the plants which should therefore be burned when the rust ap- pears. See p. 96. HIBISCUS, ROSE-OF-SHARON Canker {Cytospora) . — Death of twigs or of whole plants results. Diseased parts are thickly covered with wart-like, black pycnidia. HOLLYHOCK Rust (Puccinia malvacearum Mont.). — This rust, native to Chili, was introduced into France about 1868. It spread rapidly over all Europe, from whence it came to the United States about 1886 upon infected seed. It was rapidly dis- seminated throughout this country, and is now known from Maine to Louisiana, in many places rendering the plants un- sightly. It is easily recognized by its yellow to brown sori, each sorus considerably raised above the surface of the leaf 424 Diseases of Economic Plants or stein as a small, wart-like protuberance. Badly rusted leaves, or even whole plants, wither and die as though blighted. In mild cases the leaves remain green and the plant may bloom. It is recommended to sponge the diseased parts with permanganate of potash: two tablespoonfuls of saturated solution diluted with one quart of water. Leaf-spot {Cercospora althicena S^Ccc). — Upon the leaves and other green parts of the hollyhock, velvet leaf, and mal- low rather large, dark, angular spots are produced in abund- ance, each spot with a dark border and an ashen center upon which numerous, black hyphse may be seen. Badly diseased leaves fall, and by midsummer only dead, leafless stalks may remain. Even in mild cases, by decreasing the amount of green surface, the spots both injure the appearance of the plant and lessen productiveness. Spraying with Bordeaux mixture or ammoniacal copper carbonate at intervals of about ten days is thoroughly effective. Leaf-spot {Phyllosticta althceina Sacc). — This pest, long known in Europe, is recognized as large, brown, circular spots, 1-2 cm. or more in diameter, upon the leaves. The centers are brittle and usually break away irregularly. Anthracnose (Colletotrichum malvarum (B. & C.) South.). — Since about 1885, this disease has been noticed in destruc- tive form in greenhouses, particularly in the propagating beds; in some cases to such serious extent as to nearly pro- hibit commercial culture of the hollyhock. It occurs upon any green part of the plant. On the leaves it forms brown spots and causes withering; upon young succulent petioles or stems, collapse of the parts beyond follows; if the parts be older, sunken spots varying from light yellow to black are produced. The plants should be sprayed with Bordeaux mixture as soon as the first leaves appear and every second day there- after. Angular leaf-spot (Septoria) is also common. Ornamental Plants 425 HYDRANGEA Leaf-spot (Phyllostida hydrangece E. & E.). — Large, rusty, brown blotches occur upon the leaves, in some cases to such extent that the tops of the plants must be cut awa3% to the entire destruction of their decorative value. Rust {Pucciniastrum hydrangece (B. & C.) Arth.) is common and often serious. Leaf-spot {Cercospora sp.). — Small, round, or angular white spots with a very small amount of dark hyphal growth in the centers are common upon this plant. The spots are definit^e and are bordered by a narrow reddish purple Hne. IRIS Leaf-spot ''-^ (Didymellina iridis (Desm.) v. H., Heterospo- rium). — The disease occurs only on the German iris, affect- ing mainly the upper portion of the leaf with oval spots with water-soaked margins. Dead leaves should be removed as soon as the snow melts away. IVY {Hedera) Blight {Vermicularia trichella Fr.). — This blight usually begins midway between base and apex of the leaf, and is especially common upon the white portions of the variegated varieties. The diseased portions turn black, and small black acervuli appear. LAUREL, MOUNTAIN (Kalmia) Leaf -blight {Phomopsis kalmice Enl.). — Dead spots ap- pear on the leaves and may involve the entire blade, later ex- tending to the stems and even killing entire plants. Leaf- spot {Septoria kalmicola (Schw.) E. & E.) is of common occurrence. 426 Diseases of Economic Plants LARKSPUR A black leaf-spot due to bacteria has been noted in Massa- chusetts. Drop (Sclerotinia) . — See lettuce. LILAC Powdery-mildew (Microsphoera alni (Wallr.) Salm.). — The characteristic spots of the powdery-mildew, white and flour-Hke, are frequent upon the lilac. Black perithecia are abundant late in the season. Leaf-spot (Bacteria) is of minor consequence. LILY Gray-mold ^"'^ {Dotrytis sp.). — This exceedingly destruc- tive mold of the lily was noted about 1885, and was first closely studied by Ward in 1888. It makes its appearance in the spring as small, orange-colored spots upon the leaves and buds. These enlarge, and later become coated with a light brown, dusty, fuzzy mold which destroys the leaves and blossoms, often leaving only the naked stalks standing. Sclerotia much like those described under lettuce drop appear in association with the decay in its late stages. Their subsequent history is like that of lettuce sclerotia. Bermuda lily-disease. ^^^ — The plants are stunted and the leaves are distorted and bear spots that are yellowish to white and usually sunken. Frequently a commercial loss of from 20 to 60 per cent follows. No parasite is present, and the actual cause of the disease is unknown. Rogueing in the field to eliminate affected bulbs is necessary. LILY-OF-THE-VALLEY Drop {Sclerotinia sps.). — See lettuce. MIGNONETTE Leaf-spot ^^"^ {Cercospora resedce FcL). — This disease occasionally ruins the greenhouse crop. The spots are at Ornamental Plants 427 first minute, pale, with brownish or yellowish borders, or they spread over the leaf as a reddish discoloration. In late stages they are uniformly brown, with dark hyphae scattered over the central portions. The dead areas enlarge irregularly, and the leaves finally curl and die. Bordeaux mixture and ammoniacal copper carbonate, used once a week, have proved effective remedies. MORNING-GLORY, MOON-FLOWER The following are common but usually not serious: Rust (Coleosporium ipomoece (Schw.) Burr.); White-rust (Albugo ipomoece-pandurance) ; Leaf-spots due to various fungi. NASTURTIUM (Tropoeolurn) Blight {Pseudomonas aptaium). — In this disease the leaves are wilted and bear water-soaked spots usually about 3-5 mm. in diameter. Black-mold (Pleospora tropoeoli Hal., AUernaria). — The leaves which are affected turn light green, later yellow, and still later are covered with a black mold. Damping-off (Colletotrichutn). — Damping-off due to a species of Colletotrichum is common in the cutting-bed. The diseased parts bear numerous black acervuli. White-rust (Albugo Candida) occurs rarely. OLEANDER Knot, gall '*''''' (Bacillus). — This disease both upon leaves and stems appears to be identical in character with that upon the olive. ORCHIDS Mold (Botrytis). — The presence of straw-colored spots often renders the plants unsightly and the flowers valueless. A gray mold similar to that found upon the lily appears later. All infested refuse should be burned. 428 Diseases of Economic Plants Numerous anthracnoses, leaf-spots, rusts, and other dis- eases also occur on orchids. Their discussion would involve many pages. See also, p. 412. PALM Anthracnose {Colletotrichum) . — Palms often die and turn black at the tips of the leaf segments, or similar spots may appear upon other parts of the leaf. These spots near their edges have a watery appearance. When they become dry, purplish acervuli appear. Upon seedlings the disease is par- ticularly troublesome, resulting in failure of the leaves to unfold. The blighted parts should be cut away and burned and the remaining foliage sprayed at least once each week with Bordeaux mixture or ammoniacal copper carbonate. Graphiola blight {Graphiola phmnicis (Mong.) Poit.). — Small, gray, tubercular growths, 1-2 mm. in diameter, appear scattered over the leaves. In greenhouses the disease is commonly present but not in destructive form as it is further south in the open. Numerous other leaf-spots also occur on the many varieties of palms. PANSY. See violet. PEONY Mold 448 (Botnjtis). — This mold was first noted in 1897 in Europe. It has since been reported in Canada, Massachu- setts, Rhode Island, Pennsylvania, and Maryland as causing serious loss. Young plants are attacked almost as soon as they appear above ground, and ashen gray spots are produced upon the bud-scales, and stems. Among older plants the rot develops upon the leaves, unopened buds, and at the base of the stem. Brown mold similar to that described for lettuce not in- frequently develops upon the affected parts. Numerous Ornamental Plants 429 greenish-black, flat sclerotia, 1-13^ mm. in diameter, are formed in the stems. Dead leaf and stem remains should be removed from the peonies before they are set in the ground. Bordeaux mix- ture may be used after the plants appear in the spring. Infested beds should be steamed. Drop (Sclerotinia). See lettuce. PETUNIA Drop (Sclerotinia) . See lettuce. PHLOX Powdery-mildew (Erysiphe cichoracearum DC). — This is of general distribution and injurious. Leaf-spot (Cercospora phlogina Pk.). — Brown circular spots occur on the leaves. PINK Rust (Pucciriia arenarioe (Schm.) Schr.). — This rust was described in 1803 by Schumacher. It is quite common upon various members of the pink family, for example, chick- weeds, corn cockle, Bouncing Bet, etc. The sori are large, raised blisters arranged in characteristic concentric circles. Diseased plants should be burned. PRIMROSE Leaf-spot {Phyllostida primulicola Desm.). — Large, cir- cular, brown, dead spots are produced upon the leaves. Minute dark pycnidia may be seen. Leaf -spot {Ascochyta primulce Trail) . — Well-defined oval spots, resembling those of the phyllosticta leaf-spot, are formed. These two diseases cannot be distinguished without the aid of the microscope. Leaf-spot {Ramularia primulce Thuem.). — In this disease the blotches are yellow with centers of ashen whiteness. No pycnidia are present, but instead a gray coating of mold. Anthracnose (Colletotrichum primulas Hal.). — In this blight 430 Diseases of Economic Plants the entire leaf is more often involved than in the above diseases, and definite spots are more rare. Dark acervuli are present. Gray-mold {Botrytis sp.). — This occurs upon leaves and flowers much as upon lettuce. Bordeaux mixture is useful with all of these primrose diseases. PRIVET Anthracnose ^"^ {Glomerella cingulata, Gloeosporium) . — Twig blight superficially resembling that of the pear is a character of this disease in its later stages, terminal parts of the twigs 2-5 cm. long being affected. The line of separation between diseased and healthy tissue is sharp through shrink- ing and depression of the diseased part. In early stages de- pressed, oblong, diseased spots, at first very minute, are seen upon the bark. These spots enlarge, eventually girdle the twig, and cause the death of the distal part. Minute black elevated acervuli, visible to the naked eye, are scattered over the surface of the original disease spots. Affected branches should be cut well below the diseased portion and burned. A spring spraying, before the buds swell, with any good dormant spray will still further reduce infection. ROSE 466 Black-spot ^''^ (Diplocarpon rosce Wolf, Adinonema) . — Both in and out of doors, this is a widely known and destruc- tive rose disease. It was first described in 1824, and is now widely distributed throughout Europe and the United States. It consists of irregular circular or oval indefinitely bordered, black spots upon the upper surface of leaves that are mature or nearly so. The larger spots are a centimeter or more in diameter, and they frequently coalesce so as nearly to cover whole leaflets. With age the spots turn gray at the centers, at which part Ornamental Plants 431 the leaf dies. They also become more regular in outline than in their earlier stages. Portions of the leaflets outside of the area actually spotted often turn yellow, and the diseased leaflets fall off prematurely. Thus the beds beneath diseased plants are often strewn with fallen leaves. All infective material should be gathered and burned, and by use of a good dormant spray both bushes and ground be Fig. 220. — Rose mildew; diseased and healthy shoots. well cleared of superficial spores. Ammoniacal copper car- bonate used once each week is effective after the plants are in foliage. Lime-sulfur or Bordeaux mixture may be used when the residue on the foliage is not objectionable. Powdery-mildew {Sphcerotheca pannosa (Wallr.) Lev. or S. humili (DC.) Burr, Oidium). — This is perhaps the most wide-spread and destructive of all rose diseases both under glass and in the open, being especially destructive to the 432 Diseases of Economic Plants rambler varieties. In mild cases it occurs merely as flour-like, dusty white patches upon the leaves. But when present, it usually becomes aggressive, attacking the young leaves and tender shoots, which become dwarfed, curled, reddened, va- riously deformed (Fig. 220), and covered with the white powder of spores and spore stalks. The vitality of the plant is so lowered by repeated attacks and even by direct attack upon the buds that the plants become worthless. Indoors sulfur is serviceable. The house should be closed and the sulfur boiled in a kettle for two to three hours twice weekly, or the house may be closed in the morn- ing, the temperature raised to 24° C. (75° F.), and the air well filled with sulfur from bellows. The temperature should then be raised to 31°-32° C. (85°-90° F.), and al- lowed to cool gradually. Either out doors or in, dusting (sulfur 90 parts, arsenate of lead 10 parts) is effective and more convenient than spraying with Bordeaux mixture or lime-sulfur. Canker '^^^ {Cylindrocladium scoparium Morg.). — Brown, dead cankers are formed on the stems and branches, or at the crown, and often encircle the stem for several centimeters. Considerable injury is done to roses under glass. Examine new stock carefully to exclude canker. If the disease enters the house remove all old soil and disinfect the benches with formalin. Brown-canker ^^^ {Diaporthe umbrina Jenk., Phomopsis) also occurs on roses of many varieties. Rust {Phragmidium suhcoriicum (Schr.) Wint.). — This true rust is common in Europe, and is found in many parts of the United States from the Atlantic to the Pacific; still it is not a very serious pest. Early in the season orange-yellow sori appear upon the green parts of the plant: on the leaf as small, circular spots; on the stems and petioles often as quite large, powdery masses. Later in the season the color of the sori changes to brick red. Affected branches should be burned promptly, and all infective material should be burned in the autumn. If Ornamental Plants 433 the disease reappears, the whole plant should be dug up and burned. In beds where the disease has occurred, a dormant spray should be applied in early spring. Another rust is due to Earlea speciosa (Fr.) Arth. — Though much like the last, this is limited in its attack to the stems, rarely petioles. The sori are irregular and black. Since the causal fungus is perennial in the stems, excision and burning are to be practiced. Anthracnose {Gloeosporium rosce Hal.). — This anthrac- nose is very similar to that of the raspberry. The diseased canes, bearing small, pale leaves, die from the tip backward for 2-3 dm., and red acervuli appear upon them after death. Often the canes become completely defoliated. Affected plants should be sprayed with Bordeaux mix- ture or ammoniacal copper carbonate. Leaf-spot (Mycosphcerella rosigena E. & E.). — The leaves are marked with gray, irregular, indefinite blotches which bear minute black perithecia in their centers. Another leaf-spot is due to Cercospora rosceicola Pass. Circular, gray spots bordered with dark purple but without pycnidia are present. Downy-mildew (Peronospora sparsa Berk.). — This mil- dew is kin to that of the grape. Its spots are indefinite, and the characteristic, downy, white to purple coating is noted upon the lower surfaces of the leaves. It is not common in America. Bronzing, its name indicating its character, occurs frequently. It is not due to parasites and does no real harm. Crown-gall. See peach. • SEDUM Leaf-spot {Septoria sedi West.). — Dark, circular blotches appear upon the leaves and result in such defoliation that the stems often become naked nearly to the tips of the branches. Infected parts should be burned. Anthracnose (Vermicularia telephii Karst.). — This disease usually appears first at the 434 Diseases of Economic Plants point of attachment of the leaves, and later it passes to the stem, causing soft rot and shrinking of the outer parts. After defoliation the disease spreads slowly toward the base of the stem. Infected parts should be burned. SNAPDRAGON Anthracnose ^■''^ (Colletotrichum antirrhini Stew.). — -This disease which often ruins the crop is the most destructive of this host, both under glass and in the open. It attacks plants of any age, producing on the stem elliptical sunken spots, 5-8 mm. long, and on the leaves circular dead spots. These are at first dirty white with narrow brown margins; later acervuli appear in the center, at first brown, then black. Diseased plants show numerous, dead, hanging leaves. The stems or lateral shoots may be girdled, killing the parts beyond. It is recommended to use only healthy plants for cuttings and to clean up and burn all diseased refuse. The cuttings should be sprayed when well rooted and repeatedly until transplanted. Excess of water should be avoided and thorough ventilation provided. Leaf-spot '""-^ {Phyllosticta antirrhini G. & A.). — Circular, brown or black spots about one centimeter in diameter, usually marked by concentric ridges, appear on the leaves. Lesions on the petioles cause death of the leaf and infection of the axils. Stem lesions may be 2 or 3 cm. long and eventually girdle the stem, resulting in death of all distal parts. Young plants die from typical damping-off. Bor- deaux mixture is recommended for forms of the disease other than damping-off, which must be met by soil dis- infection. Rust ''^^ (Puccinia antirrhini D. & H.). — This rust has recently appeared in greenhouses in destructive form. Dis- eased stock should be excluded and sub-irrigation adopted if possible. Ornamental Plants 435 SPURGE Anthracnose (Gloeosporium euphorhice Hal.)- — The attack usually begins upon the flower cluster and passes down the stem to the leaves, which then fall away, leaving the naked, blighted branches. The disease often interferes seriously with the ornamental effect of this decorative plant. SUNFLOWER, JERUSALEM ARTICHOKE Rust {Puccmia helianthi Schw.). — Both wild and cul- tivated species of sunflowers are often badly rusted. The early sori are yellow to brown, the later black. Badly rusted leaves die and much injury follows both to flower and seed. In the spring the cluster-cup stage is sometimes found upon the same host. Burning of infested refuse is the only remedy known. j)j-Qp 455 (^Sclerotinia perplexa Law.). — The disease ap- pears first in the root or lower stem and spreads upward to the heads. It in general character resembles lettuce drop. Leaf -spot {Septoria helianthi E. & K.) is common but not serious. SWEET-PEA 454 Anthracnose (Glomerella cingulata, Gloeosporium) occurs as spots on stems, leaves, and pods. Seed from diseased pods should be avoided. Powdery-mildew {Microsphcera aim, Oidium) . — This is not usually troublesome if proper greenhouse conditions are maintained. See rose. Streak {Bacillus lathyri M. & T.). — Dark streaks occur on the stem. Wilt (Fusarium). — See cowpea wilt. Drop {Sclerotinia) . — See lettuce. Mosaic. — See tobacco. Root- rots are numerous, due to Nematodes, Thielavia, Corticium, and other fungi. 436 Diseases of Economic Plants TULIP Gray-mold (Botrytis) . — All parts of the host except the roots are affected. The disease was apparently imported from Europe and is now established throughout the United States. VERBENA Powdery-mildew (Erysiphe cichoracearum DC, Oidimn). — Powdery-mildew is quite common upon verbena under glass or in the open. The use of potassium sulphid, 1 ounce to 3 gallons, twice a week has proved effective. VINCA Rust (Puccinia vincce (DC.) Berk.) was apparently im- ported from Europe and does occasional damage. Vinca leaf-spot {Sphceropsis vincce Sacc.) occasionally injures leaves and stems. VIOLET, PANSY Spot-disease ^-^^ {Alternaria violce G. & D.). — This is one of the widespread and destructive violet diseases. It attacks the plant at any stage of its growth and upon any green part, but is most destructive upon the foliage. It first appears as small, definite, circular, greenish or yellowish-white spots, varying from mere dots to 1 mm. in diameter. The light cen- ter is surrounded by a narrow ring, usually dark brown to black, but turning lighter with age. As the spot enlarges the freshly diseased tissue is usually watery and translucent, and the center changes to yellow or gray-white and may fall out. Frequently by the combined effects of several spots the whole leaf is destroyed. If the air is damp, a thin coating of rusty-colored spores may be seen in the old spots. Damp, warm, cloudy, summer weather, unclean houses, Ornamental Plants 437 weak plants, poor stock, poor beds, are predisposing con- ditions to disease. To avoid the disease the houses shoukl be kept scrupu- lously clean, only strong stock used, infested material picked and burned, and insects banished. Close attention must also be given to ventilation, heating, shading, and watering. The soil should be removed each season and every means used to produce strong resistant plants. Other leaf-spots are due to Cercospora violce Sacc, Phyllosticta violce Desm. and Marssom'na violce (Pass.) Sacc. No pycnidia are present, but the centers of the spots are darkened by the presence of hyphse. Anthracnose "^^^ (Colletotrichum violce-iricoloris RES.). — This blight has been noted in many states. It is characterized by the appearance of dead, black-bordered spots on the leaves and petals, thus disfiguring the flowers, and affecting the production of seed, or even bringing premature death to the plant. Thorough and frequent spraying with Bordeaux mixture is advocated. Wilt ^^'^ (Fusarium violce Wolf). — This was noted as of economic importance in Nebraska, where it caused sudden dying of apparently healthy plants. Slightly sunken areas were evident on the stems just above the ground, and the roots were reduced to mere stumps. Rust (Puccinia violce (Schm.) DC). — One of the most common of pansy diseases is this true rust which affects all aerial parts of the plant. It is recognized by its sori. Downy-mildew (Peronospora violce De Bary). — The downy-mildew is in general character like that of the grape. The spots are indefinite, and affected plants droop and die. Anthracnose {Glceosporium violce B. & Br.). — The an- thracnose often begins at the edge of the leaf, as an irregular discoloration which extends inward, eventually blighting the whole leaf. Root-rot {Thielavia). — Affected plants are stunted and yellow. The underground parts show numerous dark spots 438 Diseases of Economic Plants Fig. 221. — Violet leaves, healthy and affected by spot-disease. After Dorsett. Ornamental Plants 439 of dead tissue which often involve the roots for considerable distances. The disease is the same as that of tobacco. Root- rot (Corticium), see p. 21. Mold {Zygodesmus albidus E. & H.). — This mold forms a white, flour-like coat over the leaf. VIRGINIA CREEPER (Ampelopsis) Leaf-spot {Guignardia hidivellii, Phyllosticta) . — The spots occurring upon the leaves and shoots are identical in ap- pearance with those upon the grape, and the same treatment is recommended. Powdery-mildew. See grape. Stem-rot {Cladosporium herharum Lk.). — Large blanches or even the entire plant may be killed. WATER-LILY Leaf-spot (Cercospora) . — Circular spots, at first pale green, later yellow, and finally brown and dead, are produced upon the leaves. The dead tissue may break away, leaving irregular holes. Soda-Bordeaux mixture is recommended, since it is effec- tive and does not spot the leaves. It is beneficial also in removing undesired algal growth. Another leaf-spot is due to Helicosporium nymphcearum Rand. — Dark spots often red-bordered occur on the leaves and may enlarge to involve the whole leaf. FUNGICIDES* Bordeaux mixture. ^^4' ^^''' ^^^^ ^^^^ '^^^ — The 4-4-50 formula (4 pounds of copper sulfate crystals and 4 pounds of stone- lime to 50 gallons of water) is one in common use. According to the common formulas several times as much lime is used as is necessary to precipitate the copper. A mixture used abroad, known as the Woburn mixture, calls for a solution of copper sulfate with lime water and subsequent dilution as contrasted with milk-of-lime used in the ordinary Bordeaux mixture. According to Pickering ordinary Bor- deaux mixture and the Woburn mixture, containing only one-sixth as much copper, seem to be equivalent in fungicidal action. To make large quantities of Bordeaux mixture, or small amounts repeatedly, it is desirable to prepare separate con- centrated stock solutions of copper sulfate and of lime. These are made up at the rate of approximately one pound of each to the gallon. In preparing a stock solution of copper sulfate, a weighed amount of the commercial crystals, ''bluestone, " is placed in a sack and suspended in water in a barrel or other wooden vessel. The volume of the water should equal in gallons the weight of the copper sulfate in pounds. The solution, as formed, will flow to the bottom, leaving comparatively fresh water in contact with the re- maining crystals. Stirring partially defeats the purpose of this method by increasing the concentration of copper sulfate in the liquid in contact with the undissolved part. If the copper sulfate is placed in the bottom of the barrel, it will dissolve but slowly even with frequent stirring. When dissolved, the solution should be made uniform by stirring. In preparing the stock solution of Hme (the term in com- * Prepared by W. A. Ruth. 440 Fungicides 441 mon use in this connection for a suspension of calcium hy- droxid) a definite quantity of fresh stone-lime is placed in a trough, slaked, and made up to a volume corresponding in gallons to the weight of the lime in pounds. In slaking the lime a small quantity of water is used to start the reaction, and just enough water is added, as the lime slakes, to prevent crumbling. The lime and water are stirred from the time the lime starts to slake until the reaction appears to be complete. Fig. 222. — A convenient arrangement for mixing Bordeaux mixture. After Vermont Agr. Exp. Sta. Instead of diluting to the final volume at this point, it is somewhat desirable to add just enough water to prevent drying out and to allow the mixture to cool before the further addition of water. This procedure permits further slaking, which results in a noticeably creamier stock solution, with fewer particles of unslaked lime to clog the nozzles. The common method in use in making Bordeaux mixture in the field has been to dilute the required quantities of copper sulfate and lime separately to half the final volume 442 Diseases of Economic Plants required and to pour them together into a separate con- tainer, usually the tank of the sprayer. The colloidal sus- pension obtained by this method of mixing settles very slowly and can be applied with the maximum uniformity. To make 200 gallons, the content of the usual power sprayer, by this method, an elevated platform, or a series of elevated platforms, is required. The diluted lime and copper sulfate are run simultaneously from 100-gallon wooden contain- ers standing on the platform into the sprayer, or into an elevated 200-gallon tank, where the resulting Bordeaux mixture is held in readiness to supply the power sprayer while the smaller containers are being refilled. The above method is open to improvement because of the large amount of apparatus and labor involved. Hawkins claims "a Bordeaux mixture in which the sus- pension of the copper compound settles out slowly may be prepared by adding the concentrated calcium hydroxid to the diluted copper sulfate solution or vice versa, pro- vided the mixture is sufficiently agitated." He states that *Hhe agitation necessary for preparing Bordeaux mixture with a low rate of subsidence by this method could hardly be obtained in practice except by means of a power outfit pro- vided with a good agitator." This method can be used to advantage with the tank-filler, a jet pump, with which any power sprayer can be equipped, which permits the rapid filling of the spray tank by means of the spray pump. The construction of a platform and the expense of pumping water into the elevated containers are thereby obviated. Sixteen gallons of stock copper sulfate or lime is first diluted in the spray tank to within sixteen gallons of the final volume, the stock solution of the other component is poured in, and the mixture is thoroughly agitated. A method very similar to this has proved satisfactory in the field and is in common use in Illinois. Wooden containers should always be used for the copper sulfate solutions, and the lime or Bordeaux mixture, should always be strained before it enters the tank. Fungicides 443 Lime-sulfur.''^^ — This fungicide (the material is also used in the control of San Jose scale) is prepared by boiling, in water, lime and sulfur in the proportion of approximately two parts of sulfur to one of lime. The products in the resulting solution are calcium thiosulfate (CaS203), calcium tetrasulfid (CaSi), and calcium pentasulfid (CaSs). The material may be made by the orchardist or bought from manufacturers. The commercial product is more concen- trated than that made by the formulas usually recom- mended for home use, and contains a higher proportion of polysulfid sulfur (that is, sulfur in the form of CaS4 and CaSs). The combination of constituents ^^^ that appears best to meet the largest number of desirable conditions is the follow- ing, stated in round numbers: 36 pounds of lime (pure lime, CaO, used as a basis). 80 pounds of high grade, finely divided sulfur. 50 gallons of water. When lime containing impurities is used, more than 36 pounds must be taken in order to obtain 36 pounds of pure lime. Use 38 pounds of lime containing 5 per cent of impurities (95 per cent pure). Use 40 pounds of lime containing 10 per cent impurities (90 per cent pure). No lime should be used which contains more than 10 per cent of impurities. If the lime contains impurities (oxid of magnesium, iron, aluminum, etc., and carbonates of mag- nesium, calcium, etc.), these do not go into solution but re- main as sediment, together with any undissolved sulfur not acted upon because of insufficiency of pure lime, due to impurities in the lime used. The amount of sediment thus formed can be utilized as a measure of the amount of im- purities existing in the lime. The level of the mixture during boihng should be kept near the 50-gallon mark — not being allowed to drop more than an 444 Diseases of Economic Plants inch below — this regulation is accomplished by adding water from time to time in the required amounts. It is preferable to add water in small amounts at frequent intervals rather than larger amounts less often, since the boiling is less interrupted. When the boiling is completed, the level of the liquid should be made up to the 50-gallon mark, if not already there. It will be found to have a density of 24° to 25° Baume when cooled to about 16° C. (60° F.). One gallon of this solution may be diluted with 25 gallons of water for summer use as a fungicide. Commercial solu- tions, which usually test about 33° Baume, may be diluted with 40 parts of water. The degree of dilution has relatively slight effect, however, upon the fungicidal properties of the solution, in comparison with the effect of thoroughness of application, and the amount of dilution may vary within wide limits. Another method for making lime-sulfur consists in the use of live steam, furnished by a boiler, and led into wooden barrels or tubs, in which the mixture is boiled (Fig. 223). Large tubs provided with mechanical agitators are sometimes used. Less water is needed than is called for by the formula given above, because of the condensation of the steam used in heating. Self-boiled lime-sulfur wash. — The self-boiled lime- sulfur wash is a combination of lime and sulfur boiled with only the heat of the slaking lime, and is primarily in- tended for summer spraying of peaches. Peach foliage is so susceptible to spray injury that ordinary Bordeaux mixture cannot be used as a summer spray; neither can the sulfur washes which contain any considerable quantity of sulfids in solution. The self-boiled lime-sulfur wash, however, when prepared as a mechanical mixture of lime and sulfur with only a small percentage of the sulfur in solution, is not injurious to peach foliage and has proved to be a good fun- gicide. The mixture that appears to be the most satisfactory is composed of Fungicides 445 Lime 8 pounds Sulfur 8 pounds Water 50 gallons This can best be prepared in rather large quantities — 16 pounds, or even 32 pounds at a time — so as to get enough heat to produce a violent boiling for a few minutes. Place the Fig. 223. — Making lime-sulfur wash. After Sherman. lime in a barrel and pour on enough water (about 3 gallons to 16 pounds) to start it slaking and to keep the sulfur off the bottom of the barrel. Then add the sulfur, which should first be worked through a sieve to break up the lumps, and finally enough water to slake the lime into a paste. Con- siderable stirring is necessary to prevent caking on the bot- tom. After the violent boiling which accompanies the slaking of the lime is over, the mixture should be diluted ready for use, or at least enough cold water added to stop the cooking; 446 Diseases of Economic Plants 5 to 15 minutes, according to whether the Hme is quick-acting or sluggish, are required for the process. At the end of 30 or 40 minutes, if the hot mass is permitted to stand undiluted as a thick paste, a liquid is produced that is dangerous to peach foliage and in some cases even to apple foliage. The mixture should be strained through a sieve of 20 meshes to the inch in order to remove the coarse particles of lime, but all the sulfur should be worked through the strainer. Hot water may be used to good advantage in preparing the mixture with sluggish lime, but with quick-acting lime hot water is not best. The mixture may be kept for a week or more without deterioration, but it should be thoroughly stirred before using. In applying the self-boiled lime-sulfur wash the spray- ing outfit should be equipped with a good agitator. The agitator of the ordinary barrel sprayer is not usually ade- quate. Sulfur-dust. ^^^' ''^^' ^^"' ^^^' ^^- — Very favorable reports have appeared recently of the results secured by the use of sulfur dust as a fungicide for apple scab in New York. Results obtained by experiments carried on further south have not been favorable to its use for this purpose. Thus Giddings states that as the result of four years' trial it can not be recommended for use on apples where scab or sooty blotch is severe, or for the treatment of bitter-rot, black-rot, or blotch. Brock finds in Illinois that spraying is much superior to dusting for the control of fungi, but believes that in favored localities, where fungi are comparatively easy to control, the sulfur dust has its uses. Reddick and Crosby recommend, for the average Western New York conditions, a mixture containing 85 per cent of exceedingly finely ground sulfur (especially ground, ''super- fine") and 15 per cent of dry arsenate of lead (the ''fluffy" sort is used for this purpose). The exact quantity of mate- rial to be used per tree will be determined by the wind, the size and the shape of the trees, and also by the thorough- Fungicides . 447 ness of distribution effected. From 1.25 to 2.5 pounds are ap- plied per tree in each application. '^ In localities where apple scab is less abundant than in the lake counties, as seems to be the case in most of the Hudson River section, the quantity of sulfur applied per tree may be reduced. It would be well, however, to regard these as minimum amounts until expe- rience has shown that they can be reduced with safety." Dusting appears to be slightly more expensive than spray- ing. The cost of materials is higher, but this factor in the total cost is partiall}^ overcome by the lower cost of applica- tion. The chief advantage in dusting, however, lies in the extreme rapidity with which the dust can be applied. This appears to permit the application of the fungicide at periods when the weather conditions favor infection with apple scab, and to result in comparative flexibility in the spray schedule. Ammoniacal solution of copper carbonate. — This solution contains no sediment, and on drying leaves no unsightly marks. It may therefore be used when the spotting that the Bordeaux mixture causes precludes the use of that fungicide. The mixture consists of a solution made by dis- solving copper carbonate in ammonia-water in the following proportions : Copper carbonate 6 ounces Ammonia, about 3 pints Water 50 gallons Weigh out the proper amount of copper carbonate. Set a very small portion of this aside, and dissolve the remainder of it in diluted ammonia, using only enough ammonia to dissolve it. Then add the portion of copper carbonate which was reserved. This will insure the use of no more ammonia than is necessary. It is better to have a little too much of the carbonate in the solution than to have too much ammonia. The strong solution made in this way can be diluted with the proper amount of water. The copper carbonate may be purchased directly from the drug-store, or it may be prepared at home. 448 . Diseases of Economic Plants To make copper carbonate proceed as follows: Dissolve 10 pounds of copper sulfate in 10 gallons of water. Also dissolve 12 pounds of carbonate of soda in the same amount of water. Allow these two solutions to cool, then mix them slowly together, stirring in the meantime. Allow the mixture to settle about 12 hours, pour off the liquid, and add water equal in amount to the liquid poured off. Stir thoroughly and allow it to settle as before. Repeat this operation again, then drain off all the liquid possible, and dry the blue powder which remains. This powder is the copper carbonate. Burgundy mixture. Copper sulfate 2 pounds Sodium carbonate (sal soda) 3 pounds Water 100 gallons Each chemical should be dissolved separately in half the water, then mixed as in making Bordeaux mixture. This mixture may be used, as may ammoniacal copper carbonate, when it is advisable to avoid the spotting of fruit which would result from use of the Bordeaux mixture. Copper sulfate solution, 1-17. — A solution consisting merely of copper sulfate and water to kill spores on the bark and supports may be used before the leaves appear. Dissolve the copper sulfate as in preparing the Bordeaux mixture, dilute it to the required strength, and spray upon the trees. The addition of a little lime, one half pound to 50 gallons of mixture, enables the operator to see exactly what portions of the tree have been sprayed. This mixture must not be used after the leaves appear. Potassium sulfid solution. Potassium sulfid (liver of sulfur) 1 ounce Water 2 to 4 gallons This solution should be freshly prepared. It is used as a substitute for the Bordeaux mixture, to avoid spotting, in Fungicides 449 the same way that the ammoniacal sohition of copper car- bonate is used. Potassium sulfid is also especially efficient as a protection against the powdery-mildews. Formalin. — Formalin is a very powerful germicide which came into wide use about 1889. Its interest to the farmer lies chiefly in its power to prevent the potato scab, onion smut, and the various smuts of cereals. Full directions for its use are given under special crops. This substance appears on the market under two names: '' Formalin" and ''37 per cent formaldehyde." These sub- stances are absolutely identical, and since the formaldehyde solution is cheaper, owing to the fact that the word "For- malin" is protected by patent, the customer will of course do well to purchase the 37 per cent solution. Corrosive sublimate. Corrosive sublimate 1 part Hydrochloric acid 2 parts Water 1000 parts This is employed chiefly as a seed disinfectant particu- larly for black-rot of cabbage. It is intensely poisonous and should be so regarded. Flowers of sulfur. — This substance is chiefl}^ employed as a specific for the powdery-mildews. See grape, p. 122. Proprietary fungicide s.^^^ — There are several proprie- tary fungicides on the market. Of five tested on apples in 1916, at the Illinois Experiment Station, four produced serious foliage injury and more or less serious injury to fruit. There are several commercial Bordeaux pastes on the market. Wallace has shown that none which he tested remains in suspension as well as fresh home-made Bordeaux mixture (some are very poor in this respect) and that they are very expensive if diluted to contain a copper content equal to that of 4-4-50 Bordeaux mixture. Combined fungicide and insecticide. — When an insecti- cide and a fungicide are to be used at the same time, it is 450 Diseases of Economic Plants usually possible to combine the two so that only one applica- tion is necessary. The stomach poison which is commonly used for spraying tree fruits is lead-arsenate. It comes in two forms, the powder and the paste. The latter contains 50 per cent of water. The powder should be the fluffy, finely di- vided kind. Either form may be used with Bordeaux mix- ture or boiled or self-boiled lime-sulfur. The powder is used at the rate of 1 pound to 50 gallons of spray, the paste at the rate of 2 pounds to 50 gallons. Paris green can not be used with lime-sulfur, at least in spraying tree fruits, because of the resulting foliage and fruit injury. When used with Bordeaux mixture for spraying other plants it may be made up at the rate of 5 ounces to each 50 gallons of spray. Calcium arsenate seems to be a promising stomach poison for use with Bordeaux mixture or lime-sulfur. Nicotine preparations for the control of plant lice can be used with lime-sulfur, or with lime-sulfur and lead arsenate. There have been reports indicating that it should not be used with Bordeaux mixture. Bordeaux injury. ^^^' ''^"' ^^^ — Many plants sprayed with Bordeaux mixture assume a deeper color and are more vigorous and live longer than unsprayed plants, even in the absence of fungous attacks. The potato is a notable exam- ple. Other plants are injured to a greater or less extent. The peach, plum, sweet cherry, and apricot are so severely af- fected by Bordeaux mixture that this fungicide is not used in spraying them. Ever since the first trials of Bordeaux mixture upon the apple, some injury has been noted upon both leaves and fruit, due to the mixture itself. The amount of injury differs with different varieties and with other conditions. Water, deposited as rain or dew on the surface to which Bordeaux mixture has been applied, is a necessary contributing cause. As the season advances the foliage becomes more susceptible. On the other hand, the fruit is most susceptible early in the season. The most damage to the fruit occurs from the spray Fungicides 451 applied just after the petals have fallen, and even the most susceptible varieties become almost completely immune within a period of six or ten weeks after this stage. On the fruit, injury is manifested by the formation of small black specks or the surface is russeted, sometimes very severely, and the fruit may be split or otherwise distorted. Injury to the foliage may first appear a few days after spray- ing or may be delayed for several weeks. Brown, dead spots are frequently caused, which may be followed by the yellow- ing and falling of the leaf. Yellowing may occur, however, when no brown spotting is observed. Before the discovery of the fungicidal properties of lime- sulfur and its efficiency as an early summer spray, various methods were suggested for the mitigation of Bordeaux in- jury. At present, lime-sulfur has very largely replaced Bordeaux mixture for use in the early summer. There are, however, circumstances under which Bordeaux mixture is still used at this season. It is generally conceded that lime-sulfur, applied with sufficient frequency, gives as good control of apple-scab as Bordeaux mixture, but that it is less adhesive and must be applied more frequently. Since the period when the trees are in blossom is sometimes pro- longed by adverse weather conditions, Bordeaux mixture is still consistently used by some fruit growers for the pre- bloom spray, on varieties locally subject to severe injury from scab. Bordeaux mixture may be used for the early blotch sprays on varieties not subject to Bordeaux injury, for all varieties in the control of bitter-rot and blotch after the period of immunity to serious Bordeaux injury has been attained, and of course for the entire program for varieties immune to this form of injury. Hedrick ^^^ has published an extensive list of apples classi- fied as to their immunity or susceptibility to Bordeaux in- jury. Lime-sulfur injury. ^^^-^^^ — Lime-sulfur injures many plants very seriously. Slight injury to the leaves of apples is of common occurrence. It is not usually of great consequence 452 Diseases of Economic Plants or of a lasting nature. The injury consists of irregular brown spotting, especially where the spray accumulates immediately after its application. If, however, the leaves" have been injured by apple-scab, previous to the application of the spray, the damage done to the foliage is very serious. There is no marked degree of varietal susceptibility with apples. The injury occurs soon after the spray has been applied, not, as in the case of Bordeaux injury, at a period which may be long after its application. The foliage is least susceptible to injury soon after it has unfolded. Talbert states that the dormant spray consisting of commercial lime-sulfur, testing 33° Baume, may be applied to apple trees diluted 1 to 7 or 1 to 8 after growth starts and until the trees begin to bloom, without material injury to the leaves or flower buds. This is a much higher concentration than is usually used when the trees are in foliage. Lime-sulfur injury to the fruit occurs occasionally, as the result of drenching. It is generally conceded that injury to the fruit occurs if lime-sulfur is used in hot weather, after the fruit has developed to approximately the size at which it becomes relatively immune to Bordeaux injury. From this stage onward, Bordeaux mixture is again used, regardless of the foliage injury produced. Lime-sulfur injury may, however, result from the application made just after the petals fall or those just following. Spraying Apparatus Whether for spraying a small garden or a large commercial orchard proper apparatus is needed. The chief types of pumps are briefly mentioned be- low. Bucket pumps. — These pumps are suited for use in the garden; to spray the bushes or a few small fruit trees in the yard. The fact that they may be used in any ordinary bucket or pail gives them an advantage oyer some of the other outfits. By the attachment of a foot rest which ex- Fungicides 453 tends outside the pail to the ground, the pump can be held firmly. Compressed air sprayer. — After the tank is partly filled with the spray mixture and closed, air is pumped in, thus pressure is exerted upon the liquid, which is Fig. 224. — • Bucket pump showing hose, nozzle, and bucket attachment. After Gould Mfg. Co. Ficj. 225. — Barrel pump showing agitator. After Gould Mfg. Co. forced out in the form of a fine spraj' when the nozzle is opened. This type of sprayer is satisfactory in some instances, and is adapted to about the same fields as the bucket pump. It is not well adapted for spraying large areas, since the sprayers are inconvenient to carry, are slow and heavy. 454 Diseases of Economic Plants Knapsack sprayers. — These consist of 3 to 5-gallon tanks, with straps so attached that the outfit can be car- ried upon the back in the manner of a knapsack. The handle is so adjusted that it is operated in front of the carrier. These pumps are best adapted to spraying crops which grow breast high, as grapes. They may also be used in spraying small trees. For general garden use, Fig. 226. — ■ Modern power sprayer, equipped with high-pressure, slow-speed pump, with large bearings, ball valves, modern pressure regulator, etc. Such a machine is constructed to turn in a small space. A tower can be set on the tank for spraying tall trees with extension rods. or small areas, a half acre to an acre, they are to be recommended. Barrel pump. — For home orchard work the barrel sprayer is of most importance. The pump is adjusted to a barrel, at either the side or end. It should be provided with a good agitator to keep the spraying mixture stirred while in use. Field sprayers. — This sort of sprayer is used in spray- Fungicides 455 Fig. 227. — The power sprayer in use for spraying orchard trees. 456 Diseases of Economic Plants Fig. 228. — Power sprayer used in shade trees. Fig. 227. Smaller ma- chines differ essen- tially only in capacity. The adaptation of such outfits to various purposes is shown in Figs. 228, 229. The Spray Gun. — A recent development in power spraying is the spray gun. By its use one man can ing low plants, such as strawberries, potatoes, tomatoes, cabbage, etc. Several nozzles are attached and several rows can be treated at one time. Where a number of acres of truck crops are grown, this sprayer is of great advantage. Power sprayers. — For operating commer- cial orchards, power sprayers are a neces- sity, and are almost necessary for large home orchards, con- sisting, for example, of 50 or 60 large ap- ple trees. A modern power sprayer for use in large orchards is illustrated in Fig. 226, a still larger one in Fig. 229. — Power sprayer adapted to spraying beans. Fungicides 457 "^\ t\y^. ^W' <*■ -^-u*. '^'i Mf '. --w^ ■ ^ Fig. 230. — The nozzles are turned at an angle to the rod so that the spray may be directed upward or downward. After Faurot. rapidly spray even the tallest fruit tree, a special device en- abling the operator to throw the spray to different distances. Spray guns are being used by many commercial growers. Conveyors. — To economize still further in time and labor, conveyors are used in many commercial orchards. These are 400-gallon tanks equipped with low-pressure, high-speed pumps, a.nd gasoline engines. The conveyor carries the spray from the mixing plant to the sprayer. Two hun- dred gallons of spray- ing material can be transferred from the tank of the conveyor to that of the sprayer in less than two min- utes. In this way the power sprayer is kept Fig. 231. — Spraying grapes. 458 Diseases of Economic Plants running almost continuously, thus sometimes doubling its output. The use of extension rods and the tower in spraying is shown in Fig. 230. Nozzles.^^^— The va- rious types of nozzles are illustrated in Fig. 234. These include the Bordeaux type (upper left corner) , the Vermorel (lower left Fig. 232. — Spraying apparatus. corner), and the eddy-chamber type. The last is the best type of nozzle for spraying, and many forms of it are on the market. The eddy- chamber angle nozzle (lower right- hand corner) is a comparatively re- cent development. Fig. 234. — Various types of nozzles. Fig. 233. — Diagram of longitudinal section of a spray nozzle showing all the parts that may be found in the eddy- chamber nozzles. O, ori- fice; EC, eddy-chamber; P, post on the direct- ing disc, DD; C, Cap; W, washer; OB, oblique supply holes; S, strainer; R, reservoir; B, base of nozzle; D, disc, C, cen- tral supply hole. After Crane. Dusting machines. — These consist of various forms of blowers driven by hand or by gasoline engines. Fig. 235 shows one of these machines in use for sulfuring. Fungicides 459 No matter what type of machine is in use, it is essential to keep on hand a supply of any parts that may be broken or Fig. 235. — Sulfuring machine in use. After Faurot. become worn out. The best companies are prompt in filling orders for repairs, but the grower cannot afford loss of even a very short time at critical periods. SOIL DISINFECTION 8-1^ Soil disinfection in the field has as yet in the main proved impracticable. All promising chemicals have been tried without avail. Electricity has not given beneficial results, and at present there is no hope of any practicable manner of ridding fields of parasites by any process of disinfection. In a few instances large applications of lime, formalin, or sulfur have proved beneficial (see sweet potato, onion, etc.), but the general practicability of such usage is doubtful. Disinfection of limited areas is, however, practicable, is largely employed, and has already resulted in great benefit, eliminating not only injurious fungi but insects and weeds as well. Cutting benches, flats, and other benches in the green- house, cold frames, and seed beds, and other small areas may be disinfected with advantage. The means to be em- ployed depend upon the area, its location, and the facilities at hand. The leading methods are given below: Baking. — Flats, pots, and other small containers of earth may often be satisfactorily disinfected by placing them upon a boiler or over a stove, or in an oven for a com- paratively long period. Permanent steam disinfectors. — A system of 13/2-inch pipes, which are perforated with 3^-inch holes on their under side at intervals of 6 inches throughout their entire length, may be placed about one foot below the surface of the soil. The pipes should run lengthwise of the bed, 18 inches apart, and be connected with a steam boiler. Before treatment the soil should be thoroughly spaded up and pulverized to permit ready access of the steam to all parts, and all fertilizers except commercial ones should be applied at this time, since fresh spores of the fungus are likely to be carried in if manure be added after disinfection. 460 Soil Disinfection 461 The seed bed should be covered with several thicknesses of old burlap or blankets to confine the heat to the soil. The steam should be applied at a pressure of from 80 to 150 pounds, since at high pressure the soil does not become so wet as when low-pressure steam is used. A treatment of from one to two hours is usually sufficient to disinfect thoroughly the soil to a depth of 18 inches. A few potatoes laid in the surfaces oil will indicate the thoroughness of the treatment by the degree to which they are cooked. The blankets may advantageously be left on for some time. While this method offers some advantages for seed beds of limited area, in that the pipes may be left in the ground and used year after year with little extra labor and may also be used for subirrigation, the initial cost of installa- tion, especially on large seed-bed areas, may be prohibitive. Inverted-pan method. — The method which has given the best results in practice, and which because of its simplic- ity and small cost recommends itself for use on large or small areas, is the invention of Mr. A. D. Shamel, of the U. S. Dept. Agr. Bur. of Plant Industry, and was devised by him to disinfect nematode-infested soils in Florida. The apparatus consists of a galvanized iron pan, 6' x 10' x 6" which is inverted over the soil and the steam admitted under pressure. The pan is supplied with steam-hose connections, has sharp edges, which are forced into the soil on all sides to prevent the escape of steam, and is fitted with handles for moving it from place to place, the weight of the entire pan being not over 400 pounds. The soil is prepared as in the greenhouse method, a few potatoes being buried at a depth of a foot to gauge the degree of heat attained, or a soil thermometer may be used if desired. The steam should be kept at as high pressure as possible, from 80 to 150 pounds being best, and the treatment should continue from 30 to 60 minutes, depending upon the pressure maintained and the character of the soil. Wet soils require more time than dry soils. In experiments conducted on tobacco seed beds in the spring of 1907, one hour's steam- 462 Diseases of Economic Plants ing at 80° C. gave best results in killing both the fungi and the weed seeds. When one section of the bed is treated, the pan is lifted and carried to another portion, and the operation repeated until the entire bed is steamed. Fig. 236. — Disinfecting with steam by the inverted-pan method. After Johnson. The inverted-pan method is particularly applicable in disinfecting greenhouse benches or flats. Streaming steam from the heating system passed into the pan for one and one- half hours suffices. A steam hose connecting the pan with a traction engine makes a serviceable out-of-door outfit. The Sargent method. — Disinfection by a system of steam pipes arranged in the form of a harrow, with hollow. Soil Disinfection 463 perforated teeth, has proved satisfactory under some condi- tions. Surface firing. — Surface firing of seed beds has been a common practice for years in some tobacco sections, par- ticularly in Kentucky and other southern states, the end in view being the improvement of the tilth of the soil and the killing of weed seeds rather than the destruction of any fungous disease. In Italy burning is now considered a part Fig. 237. — Disinfecting soil with a Sargent disinfeetor. Original. of the regular method of tobacco seed-bed preparation, it having been resorted to as a preventive of root-rot due to Thielavia. Two methods of surface firing are in vogue; the first, by direct firing, the second requiring the use of a pan. In the direct method, the land to be disinfected is first thor- oughly pulverized and manure applied. It is then covered with straw, brush, and wood sufficient to make a hot fire. This is ignited and allowed to burn an hour or so, after which the ashes are raked into the surface soil. The second method, pan firing, consists in the use of a sheet-iron pan, 3' by 9', which is set in the middle of the seed 464 Diseases of Economic Plants bed and a fire built under it. The soil on one side of the pan to a depth of 6 inches is shoveled and heated, great care being taken to keep it moist, otherwise the humus would be burned out and the physical texture seriously altered. After an hour this soil is put back and that from the other side of the pan subjected to the same treatment, and then the pan moved along to a new place. The soil underneath the pan itself is thereby subjected to heat for two hours. Disinfection by formalin. — The use of formalin for the disinfection of greenhouse soil and of tobacco seed beds against Corticium has been in vogue for some time with excellent results. It furnishes a very simple means of disin- fection as follows: The beds are thoroughly prepared as for the other methods of disinfection described and are then drenched with a 2 per cent formalin solution using two quarts of this solution to the square foot of bed space. The solution should be put on with a watering pot with a rose orifice and distributed as evenly as possible over the bed, so as to wet the soil thoroughly to the depth of a foot. It will, in most cases, be necessary to put this solution on in two or three applications, as the soil will not immediately take in this quantity of water. The beds should then be covered with heavy burlap or a tarpaulin to retain the fumes for a day or so, and then aired for a week before sowing the seed. Spring applications of formalin are open to the following objections: The addition of such a large quantity of water to the soil keeps it wet and cold longer than would naturally be the case, thus delaying germination as well as subsequent growth; the necessity of airing the beds to remove the for- malin fumes and to allow the soil to dry out also causes delay in seeding. To obviate these difficulties the beds should be treated in the fall, before freezing. Disinfection by sulfuric acid. — One-eighth to three- sixteenths fluid ounce of commercial sulfuric acid in from one to two pints of water, according to the humidity of the soil, is applied per square foot of soil immediately after the seeds are covered. This treatment is used principally for conifers. Soil Disinfection 465 Abundant watering is necessary to prevent root injury of the seedlings. Disinfection by copper-sulfate. — This chemical may be used up to one-fourth ounce per square foot. It is employed chiefly for conifer seed beds. Disinfection by zinc-chlorid. — Five-eighths of an ounce of this solution per square foot may be employed for conifer seed beds, but it is more expensive than copper-sulfate. Disinfection by hot water. ^^^ Pots, flats, etc., may be disinfected by submersion in hot water, 98° C. (208° F.) for five minutes. The quantity of water necessary increases with the volume of soil to be treated ; thus for 8" pots about 3000 cc. of water is needed at 98° C. or 2000 cc. of boiling water. On shallow benches boiling water should be used at the rate of 7 gallons per cubic foot of soil. t=—z£ =— 2fr 01- — Z5 =—Z9 to 00 cr O cfq* H go oz — ' — — = — zr OE = _ =— u Z9 Ofr- 09- =r- ZOI z:^— 211 09- ZZl 3 - oz- -JEl ZH =—251 — =z— 291 • 3 .3 i CO CO o o ?^ o wb CO oj :0 CO •^ S. 3 3 P 3 ^^ c;f P o o o tr" 1—1 CO W d CO O O, o en 3' c- isS S = -• 60 08- 06- -Zli -281 -261 -zoz •0 "J BIBLIOGRAPHY 1. Whetzel, H. H., An outline of the history of phytopathology. W. B. Saunders Co. 1918. 2. Sorauer, P., Manual of plant diseases. Trans, by F. Dorrance, Dorranceville, Pa. 1914. 3. Lodeman, E. G., The spraying of plants, 6. The Macmillan Co. 1913. 4. Stevens, F. L., Some problems in plant pathologj^ in reference to transportation. Phytop. 5: 108. 1915. 5. Coons, G. H., and Nel- son, R., The plant diseases of importance in the transportation of fruit and vegetables. Am. R. R. Per. Fr. Assn. Cir. 473. 1918. 6. Lyman, G. R., War Emergency Board, American Plant Pathologists, Midyear Rept. June 25, 1918. 7. Roberts, J. W., and Pierce L., Control of cherry leaf-spot. U. S. Dept. Agr. Farms'. Bui. 1053. 1919. 8. Beinhardt, E. G., Steam sterihzation of seed beds for tobacco and other crops. IT. S. Dept. Agr. Farms'. Bui. 996. 1918. 9. Selby, A. D., and Humbert, J. A., Methods of soil sterihza- tion for plant beds and greenhouses. Ohio Agr. Exp. Sta. Cir. 151. 1915. 10. Johnson, J., The control of damping-off disease in plant beds. Wis. Agr. Exp. Sta. Res. Bui. 57. 1914. 11. Hart- ley, C, and Pierce, R. G., The control of damping-off of coniferous seedlings. U. S. Dept. Agr. Bui. 453. 1917. 12. Gifford, C. M., The dampirg-off of coniferous seedlings. Vt. Agr. Exp. Sta. Bui. 157. 1911. 13. Peltier, G. L., Parasitic Rhizoctonias in Amer- ica. 111. Agr. Exp. Sta. Bui. 189. 1916. 14. Pammel, L. H., Fungous diseases of sugar beets. la. Agr. Exp. Sta. Bui. 15. 1891. 15. Fulton, H. R., Diseases of pepper and beans. La. Agr. Exp. Sta. Bui. 101. 1908. 16. Pammel, L. H., Cotton root-rot. Tex. Agr. Exp. Sta. Rept. 2: 61. 1898. 17. Duggar, B. M., The Texas root-rot fungus and its conidial stage. Ann. Mo. Bot. Gard. 3. 1916. 18. Gilbert, W. W., The root-rot of tobacco caused by Thielavia basicola. U. S. Dept. Agr., B. P. L Bui. 158. 1909. 19. John- son, J., Host plants of Thielavia basicola. Jour. Agr. Res. 7: 289. 1916. 20. Stevens, F. L., and Sackett, W. G., The Gran- ville tobacco wilt. N. C. Agr. Exp. Sta. Bui. 188. 1903. 21. Stone, G. E., and Smith, R. E., Nematode worms. Mass. Agr. 467 468 Bibliography Exp. Sta. Bui. 55. 1898. 22. Bessey, E. E., and Byars, L. P., The control of root-knot. U. S. Dept. Agr. Farms'. Bui. e^^7.- 481. 1918. 527. Tisdale, W. B., Iris leaf spot caused by DidjTuellina iridis. Phytop. 10: 147. 1920. 528. Hoffer, G. N., Disease free sweet corn seed. Ind. Agr. Exp. Sta. Bui 233: 1920. 529. Peltier, G. L., Carnation stem rofand its control. 111. Agr. Exp. Sta. Bui. 223: 1919. 530. Long, W. H., An undescribed canker of poplars and willows caused by Cytospora chrysosperma. Jour. Agr. Res. 13: 331. 1918. 531 Bisby, G. R., Studies on Fusarium diseases of potatoes and truck crops in Min- nesota. Minn. Agr. Exp. Sta. Bui. 181. 1919. 532. Tisdale, W. H., Bacterial blight of soy bean. N. C. Agr. Exp. Sta. Rept. 1918. 59. 533. Coerper, Florence M., Bacterial blight of soybean. Jour. Agr. Res. 18: 179. 1919. 534. Wolf, F. A., Bacterial blight of soybean. Phytop. ^0; 1920. 535. Wolf, F. A., and Cromwell, R. 0., Clover stem rot. N. C. Agr. Exp. Sta. Tech. Bui. 16. 1919. 536. 490 Bibliography Fisher, D. F., and Newcomb, E. J., Controlling important fungous and insect enemies of the pear in the humid sections of the Pacific northwest. Farms'. Bui. 1056. 1919. 537. Fromme, F. D., The Nematode disease of wheat in Virginia. Va. Agr. Exp. Sta. Bui. 222. 1919. 538. Stakman, E. C, and Levine, M. N., Rye smut. Minn. Agr. Exp. Sta. Bui. 160. 1916. 539. Byars, L. P., and Gil- bert, W. W., Soil disinfection with hot water to control the root- knot nematode and parasitic soil fungi. U. S. Dept. Agr. Bui. 818. 1920. 540. Rand, Frederick B., and Ella M. A. Enlows, Bacterial wilt of cucurbits. U. S. Dept. Agr. Bui. 828. 1920. 541. Schultz, E. S., Folsom, D,, Hildebrandt, F. M., and Hawkins, L. A., Investi- gations of the mosaic disease of the Irish potato. Jour. Agr. Res. 17: 247. 1919. 542. Meier, F. C, Control of watermelon anthrac- nose by spraying. U. S. Dept. Agr. Circ. 90. 1920. 543. McMur- ran, S. M., The anthracnose of the mango in Florida. U. S. Dept. Agr. Bui. 52. 1914. 544. Stevens, N. E., and Morse, F. W., The effect of the endrot fungus on cranberries. Amer. Jour. Bot. 6: 235. 1919. 645. Higgins, B. B., A Collectotrichum leafspot of turnips. Jour. Agr. Res. 10: 157. 1917. 546. Brandes, E. W., Banana wilt. Phytop. 9: 339. 1919. 547. Quanjer, H. M., The mosaic disease of the solanacese, its relation to the phloem-necrosis, and its effect upon potato culture. Phytop. 10: 35. 1920. 548. Botjes, J. O., Raising phloem-necrosis and mosaic free potatoes, and a source of infection whose nature has not yet been elucidated. Phj^'top. 10: 48. 1920. 549. Orton, C. R., and Kern, F. D., The potato wart disease. Penn. Agr. Exp. Sta. Bui. 156. 1919. 550. Walker, J. C, Onion diseases and their control, U. S. Dept. Agr. Farms'. Bui. 1060. 1919. 551. Stakman, E. C, The black stem rust and the barberry. U. S. Dept. Agr. Yearbook, 1918: 75. 1919. 552. Rosen, H. R., A Bacterial root-rot of field corn. Ark. Agr. Exp. Sta. Bui. 162. 1919. 553. Taubenhaus, J. J., Field diseases of the sweet potato in Texas. Texas Agr. Exp. Sta. Bui. 249. 1919. 554. Stevens, F. L., Foot-rot of wheat. Sc. N. S. 5/.- 517. 1920. 555. Greene, Laurenz and Melhus, I. E., The effect of crown gall upon a young apple orchard. Iowa Agr. Exp. Sta. Res. Bui. 50. 1919. 556. Miles, L. E., Elm leaf diseases. To be published in the Botanical Gazette. INDEX Abutilon, 407. Acal.vpha, 407. Acanthorhynchus vaccinii, 111. Acanthostigma, 379. Achillea, 407. Acremonium, 191. Actinomyces scabies, 163, 220. Actinonema, 430. Adonis, 407. iEcidium, 119, 390, 411, 423. gossypii, 350. Agave, 408. Ageratuni, 407. Agropyron, 277, 278, 340. Agrostis, 277, 278, 340. Aira, 278. Albugo, 173, 408. bliti, 164. Candida, 172, 196, 427. ipomoejB-panduranai, 250, 427. tragopogonis, 241. Alder, 361, 367, 369, 371, 379, 381. Alfalfa, 22, 23, 24, 88, 163, 321. Algal leaf-spot, 144, 147. Allseed, 163. Almond, 25, 74, 87. Alopecurus, 277, 278. Alternaria, 57, 69, 195, 217, 328, 352, 415, 427. brassicae, 169. var. nigrescens, 183. citri, 141. dianthi, 415. panax, 193. solani, 226, 264. violse, 436. Alyssum, 407. Amarantus, 407, 408. Amerosporium oeconomicum, 335. Ammoniacal copper carbonate, 447. Ampelopsis, 439. Andromeda, 409. Anemone, 407, 409. Angular loaf-spot, 114, 185, 337, 349, 424. AnthostomelLa, 145. Anthoxanthum, 277, 278. Anthracnose, 102, 112, 115, 128, 135, 143, 147, 151, 173, 180, 192, 194, 199, 241, 242, 264, 280, 300, 309, 317, 324, 328, 330, 339, 340, 342, 345, 383, 392, 395, 408, 409, 412, 424, 428, 420, 430, 433, 435, 437. Antirrhinum, 407. Aposphseria, 134. Apple, 23, 31, 87, 361, 367, 369, 372. Apricot, 74, 87, 90. Aquilegia, 407. Aralia, 408. Arbor- vitae, 367, 369, 371, 380. Arbutus, 88. Armillaria, 117, 367. mellea, 53, 370. root-rot, 79, 96, 101. Arrenantherum, 277. Arsenical injury, 240. Artichoke, 435. Ascochyta, 134, 210, 369, 379. abelmoschi, 201. armoraciae, 195. ehrysanthemi, 419. clematidina, 420. leaf-spot, 327. medicaginis, 327. primulae, 429. Ash, 23, 364, 367, 368, 369, 380, 381. Asparagus, 10, 25, 149, 407. 257, 119, 152, 217, 307, 331, 388, 421, 434, 368, 379, 491 492 Index Aspen, 359, 367. Aspidistra, 409. Aster, 22. china, 409. Asterina, 379. Aueuba, 407. Avena, 277, 278. Avocado, 135. Azalea, 113, 411. Bacillus, 427. amylovorus, 41, 62, 70, 74, 79, 101. carotovorus, 172, 173, 178, 208, 412, 420. coli, 144. lathy ri, 435. melonis, 188. phytophthorus, 231. sorghi, 307. tracheiphilus, 182. Bacteria, 217, 299, 304, 342, 369, 389, 426. Bacterial blight, 213, 337. leaf -spot, 164, 422. rot, 199. spotting, 200, 416. wilt, 260. Bacterium michiganense, 260. mori, 393. rathayi, 339. teutlium, 164. Balm, 411. Balsam, 367. Bamboo, 411. Banana, 135. Barberry, 312, 411. Bark canker, 56, 69. disease, 386. Barley, 163, 280. Barnyard-grass, 338. Barrel pump, 454. Bartonia, 407. Basswood, 372. Bean, 22, 23, 25, 152, 163. Beckmannia, 277. Bed-rot, 257. Beech, 359, 361, 364, 365, 367, 369, 380, 381. Beet, 22, 23, 25, 27, 87, 159, 163. Begonia, 24, 407, 408, 412. Bellflower, 23. Berberis, 407. Bermuda lily disease, 426. Birch, 359, 361, 364, 365, 367, 368, 369, 371, 379, 380, 381, 382. Bitter-pit, 54. Bitter-rot, 31, 69, 72, 132. Blackberry, 87, 102. Black-chaff, 319. Black-heart, 148, 235. Black-knot, 75, 97. Blackleg, 169, 231. Black-mold, 57, 69, 169, 196, 210, 213, 216, 243, 328, 331, 427. Black-root, 163, 173. Black-rot, 42, 47, 72, 120, 141, 165, 194, 247, 260. Black-rot canker, 69. Black-rust, 350. Black-scurf, 225. Black-smut, 146, 302. Black-spot, 70, 74, 79, 90, 101, 205, 217. canker, 430. Black-stem-rust, 282, 298, 305, 310, 339, 340. Black-walnut, 359. Blast, 110, 339, 380. Bletia, 412. Blight, 62, 70, 74, 79, 101, 144, 155, 165, 193, 195, 199, 203, 242, 251, 260, 282, 294, 299, 307, 324, 389, 393, 394, 403, 404, 421, 422, 425, 427. (See also early- blight, southern-blight, late- blight, blister-blight, blossom- blight, brown- blight, bacter- ial-blight, body-blight, pod- blight, stem-blight, coryneum- blight, leaf-blight, cane-blight.) Blister-cankei, 44. BHster-rust, 119, 395. Blossom-blight, 41. Blossom-drop, 265. Blossom-end rot, 263. Blossom rot, 191. Blotch, 37. Blueberry, 110. Bluegrass, 280, 338. Blue-mold, 51, 108, 132, 141, 193, 250. Index 493 Blue-stem, 110. Bluing, 397. Body-blight, 41. Boll-rot, 346. Bordeaux-injury, 450. Bordeaux mixture, 6, 440. Botryosphaeria, 346. berengeriana, 395. marconii, 353. ribis, 113. Botrytis, 10, 20, 174, 369, 416, 421, 422, 426, 427, 428, 430, 436. allii, 206. blight, 195. cinerea, 198. fascicularis, 192. rot, 134. Box-elder, 369. Breeding for resistance, 7. Bremia lactucEe, 198. Broccoli, 165. Bromus, 277, 278. Bronzing, 433. Broom corn, 283. Broom rape, 331. Brown-canker, 432. Brown-checked wood-rot, 361. Brown leaf-rust, .305. Brown leaf-spot, 395. Brown-rot, 55, 69, 73, 74, 75, 79, 101, 135. Brown-spot, 292. Brunnissure, 131. Brussels-sprouts, 163, 165. Bucket pumps, 452. Buckeye, 390. Buckeye-rot, 265. Buckwheat, 22, 165. Bud-rot, 144, 417. Bunt, 314. Burgundy mixture, 448. Butternut, 359, 361, 367, 380, 381, 382. Cabbage, 22, 23, 26, 163, 165. Cacao, 135. Cacao-disease, 245. Calamagrostis, 277, 278. Calendula, 407. California vine-disease, 131. Calla, 412. Callistephus, 407, 409. Calospora vanillse, 148. Camellia, 408, 413. Campanula, 407, 408. Candytuft, 168. Cane-blight, 105, 113. Canker, 32, 35, 42, 69, 72, 135, 137, 146, 251, 368, 385, 390, 401, 402, 405, 423, 432. (See also Pacific coast canker, blister- canker, black-rot canker, brown canker.) Canna, 413. Cantaloupe, 173. Caper, 173. Capnodium, 144, 408, 413. Carnation, 22, 87, 414. Carrot, 22, 23, 25, 173. Cassandra calyculata, 113. Castor-bean, 174. Catalpa, 25, 368, 373, 379, 380, 381, 382. Cauliflower, 23, 163, 165. Cedar, 69, 367, 383. Celery, 22, 25, 163, 174. Celosia, 407. Cenangium, 369. Centaurea, 407. Cephaleuros, 25 1 . virescens, 144, 147. Cephalothecium, 395. roseum, 49. Ceratostomella pilifera, 397. Cercospora, 201, 217, 348, 379, 439, 524. althaeina, 424. angulata, 114. apii, 176. armoraciae, 196. beticola, 159, 244. boUeana, 146. capsici, 217. circumscissa, 96. cofTeicola, 145. concors, 234. cruenta, 159, 337. fusca, 395. leaf-spot, 132, 159, 191, 327, 331. longipes, 245. medicaginis, 327. microsora, 391. 494 Index nicotianse, 257. personata, 214. phlogina, 429. resedse, 426. richardisecola, 413. rosseicola, 433. shot-hole, 96. Cercosporella albomaculans, 173. persica, 96. Cereal, 266. anthracnose, 266. nists, 275. smuts, 266. special diseases, 280. Chamaecyparis, 368, 369. Charcoal-rot, 251. Chard, 159. Charrina, 132. Cherry, 22, 25, 75, 87, 90, 96, 97, 361, 367, 369. Chestnut, 11, 87, 361, 367, 368, 369, 371, 373, 380, 381, 386, 388. China-berry, 23, 369, 372. Chive, 201. Chlorosis, 148, 265, 295. Choanephora cucurbitaruni, 191. Chrysanthemum, 23, 88, 407, 408, 418. Chrysophlyctis, 224. Cineraria, 24, 407, 420. Citrus fruits, 135. Citrus knot, 144. Cladosporium carpophilum, 82, 99. citri, 142. cucumerinum, 187. fulviim, 262. herbarum, 140, 439. macrocarpum, 243. viticolum, 132. Claviceps paspali, 340. purpurea, 304. rolfsii, 340. Cleistothecopsis circinans, 205. Clematis, 24, 407, 420. Clethra alnifolia, 113. Clitocybe, 52, 372. root-rot, 96. Clover, 22, 24, 88, 163, 328. Club-root, 26, 168, Cluster-cup, 117, 119, 350, 409. Coccomyces, 75. prunophorse, 98. Cocoanut, 144. Coffee, 144. Coleosporium ipomceae, 251, 427. senecionis, 420. solidaginis, 401, 410. Coleus, 24, 407. Collard, 165. Colletotrichum, 20, 145, 148, 151, 192, 205, 244, 251, 345, 352, 379, 427, 428. agaves, 408. antirrhini, 434. bletiae, 412. carica, 145. cereale, 280, 300, 307, 317. erumpens, 241. falcatum, 309. gloeosporioides, 135, 143, 147. higginsianum, 173. lagenarium, 180. lindemuthianum, 152. malvarum, 424. nigrum, 217. omnivorum, 409. phomoides, 264. primulse, 429. spinaceae, 242. trifqlii, 324, 330. violse-tricoloris, 437. CoUybia, 367. Colocasia, 420. Combined fungicide and insecti- cide, 449. Common-scab, 220. Completoria complens, 422. Compressed air sprayers, 453. Conifers, 355, 358, 361, 367, 368, 369, 371, 376, 379, 380. Coniothyrium, 105, 395. fuckelii, 44. Conveyors, 457. Copper-blight, 251. Copper sulfate, 448. Copper-sulfate treatment, 271. Coreopsis, 407. Core-rot, 57. Corn, 22, 88, 163, 283. Cornus, 408. Corrosive sublimate, 449. Index 495 Corticium, 20, 135, 144, 146, 163, 193, 194, 376, 402, 407, 410, 435, 439. koleroga, 145. stevensii, 47. vagum, 21, 157, 162, 165, 198, 213, 225, 257, 265, 349, 417. Coryneum beijerinekii, 87. Coryneum-blight, 74, 87. Cosmos, 407, 421. Cotton, 22, 23, 24, 88. Cottonwood, 367, 369, 372, 380, 401. Cottony-rot, 137. Covered smut, 282, 297. Cowpea, 23, 24, 26, 331. Crab-grass, 339. Cranberry, 110. Cress, 163. Cronartium, 369. cerebrum, 400. ribicola, 116, 395. Crown-gall, 51, 69, 73, 74, 79, 87, 101, 104, 132, 164, 350, 405, 408, 422, 433. Crown-rot, 144, 241. Crown-rust, 298, 339. Crown-wart, 325. Crucifers, 24, 165. Cryptosporella, 369. anomala, 389. viticola, 129. Cucumber, 22, 25, 26, 178. Cucurbit spraying, 191. Cucurbits, 24, 178. Cuphea, 407. Cupressus, 369. Curing-house disease, 259. Curl, 77, 84. Curly-dwarf, 233. Curly-top, 160. Currant, 22, 113, 367. ' Cuscuta, 325. epilinum, 352. Cutting-bench disease, 407. Cuttings, 19. Cyanospora, 369. Cyclamen, 408, 421. Cycloconium oleaginum, 147. Cylindrocladium scoparium 432. Cylindrosporium, 75, 98, 379. chrysanthemi, 420. clematidis, 420. humuli, 195. Cypress, 367. Cystospora batatae, 249. Cytospora, 78, 86, 369, 405, 423. chrysosperma, 401. Dactylis, 277, 278, 339. Dajdalea, 367. Dahlia, 24, 407, 408, 421. Daisy, 408, 422. Damage caused by plant diseases, 10. Damping off, 19, 24, 163, 173, 178, 193, 194, 198, 213, 252, 258, 265, 303, 328, 349, 352, 376, 399, 427. Dandelion, 163. Daphne, 23. Dasyscypha, . 369. resinaria, 390. Dead-arm, 129. Decay in live trees, 354. Decay of dead parts, 373. Deciduous trees, 364, 365, 367, 368, 371, 374. Dendrophoma, 353. Dewberr3^ 88, 102. Dianthus, 407, 408. Diaporthe, 369. batatatis, 250. phaseolorum, 158. umbrina, 432. Dibotryon morbosum, 75, 97. Didymellina viridis, 425. Didymosphseria, 379. Dieback, 74, 78, 86, 135, 144, 395, 402, 404. canker, 57, 69. Diplocarpon rosae, 430. Diplodia, 135, 144, 148, 187, 402, 420. cacaoicola, 245. gossypina, 346. longispora, 394. macrospora, 287. tubericola, 250. zeae, 287. Diplodina, 190. Diseases due to impure air, 26. Disease prevention, 236. 493 Index Disinfection of seeds, 7. Doassansia gossypii, 349. Dodder, 144, 325, 331, 352. Dogwood, 369, 381. Dothichiza, 369. populea, 401. Dothidea, 369. Dothidella, 394. Dothiorella gregaria, 404. Double-blossom, 108. Downy-mildew, 125, 158, 164, 171, 178, 196, 198, 203, 244, 263, 295, 327, 338, 433, 437. Dracaena, 422. Dracocephalum, 408. Drop, 26, 27, 158, 164, 170, 174, 193, 196, 258, 409, 426, 435. Drupes, 74, 368. Dry-rot, 230, 250, 287, 289, 374. Dusting machines, 458. Dwarf leaf-rust, 282. Early-blight, 176, 226, 204. Ear-rots, 286. Echinodontium, 367. tinctorum, 389. Eel-worms, 320, 412. (See also nematodes.) Egg plant, 22, 23, 25, 26, 192. Einkorn, 310. Elder, 381. Elm, 23, 25, 359, 364, 367, 369, 379, 380, 381, 388. Elymus, 277, 278. Emmer, 310. Endomyces, 57. Endothia, 369. parasitica, 386. End-rot, 112. Entomosporium, 68, 70, 379. Entyloma ellisii, 242. Ergot, 282, 300, 304, 320, 339, 340. Erigeron, 408. Eriobotrya, 407. Erysimum, 407. Erysiphe, 173, 242, 338. cichoracearum, 420, 429, 436. communis, 421. graminis, 317. polygoni, 159, 165, 187, 213, 337. Eupatorium, 408. Euphorbia, 328, 407. European canker, 55, 72, 401. rust, 116. Evonymus, 408. Exoascus deformans, 84. Exobasidium, 110, 251, 409, 411. oxycocci, 112. Extension rod, 458. Fabrsea maculata, 68, 70. mespili, 73. Falcata, 155. Favolus, 367. Ferns, 422. Festuca, 277, 278. Fiber-plant, 23, 343. Field crops, 149. Field sprayers, 454. Fig, 23, 25, 145. Filbert, 369, 389. Fir, 365, 367, 368, 369, 371, 373, 380. Fire-blight, 41, 62, 74. Fistulina, 367. Flag-smut, 316. Flax, 23, 24, 26, 350. Flower-blight, 379. Flowering almond, 408. Flowers of sulfur, 449. Flyspeck, 56, 69. Fomes, 367, 402. annosus, 53, 371. applanatus, 365. everhartii, 364. fomentarius, 364. fraxinophilus, 381. fulvus, 361. igniarius, 359. juniperinus, 383. pinicola, 365, 401. ribis, 117, 402. rimosus, 391. Foot-rot, 316. Forage crops, 321. Formalin, 449. Formalin dry method, 270. Formalin long-time treatment, 271. Formalin wet method, 270. Foxtail, 163. Frost injury, 54. Frosty-mildew, 96, 348. Index 497 Fruit-rot, 57, 134, 145, 217, 263. Fruit-spot, 57, 187. Fumago vagans, 57, 265. Fungicides, 440. Fusarium, 20, 146, 178, 213, 249, 257, 289, 318, 325, 331, 346, 376, 399, 416, 418, 420, 435. boll-rot, 346. conglutinans, 172, 409. lini, 350. lycopersici, 250. malli, 210. oxysporum, 228. rubi, 108. vasinfectum, 181, 193, 201, 331, 343. violae, 437. Fusicladium, 35, 68, 379, 402. dendriticum, 147. efifusum, 394. Fusicoccum, 129. putrefaciens, 112. Gall, 24, 113, 368, 402, 409, 420, 427. (See also crown-gall, nematode.) Garlic, 201. Gaultheria procumbens, 113. Gaylussacia resinosa, 113. General diseases, 19, 354. Geranium, 422. Gibbera, 110. Gibberella saubinetii, 318, 331. Ginseng, 24, 193. Gladiolus, 423. Gloeodes pomigena, 55. Gloeosporium, 20, 31, 44, 72, 102, 115, 145, 148, 217, 380, 395, 403, 430, 435. ampelophagum, 128. apocryptum, 392. . caulivorum, 331. euphorbiae, 435. medicaginis, 328. melongenae, 192. musarum, 135. rosae, 433. \dolse, 437. Glomerella cingulata, 31, 72, 112, 395, 421, 430, 435. gossypii, 345. piperata, 217. psidii, 146. Glume blotch, 319. Gnomonia, 380. leptostyla, 382, 403. ulmea, 388. veneta, 403. Gnomoniella, 380. Godetia, 407. Golden glow, 407. Goldenseal, 24, 195. Gooseberry, 10, 117, 367. Granville wilt, 253. Grape, 25, 87, 120. Graphiola-blight, 428. Graphiola phcenicis, 428. Grass, 23. 163, 338. Gray-blight, 251. Gray-mold, 108, 174, 192, 198, 416, 422, 426, 430, 436. Gray-rot, 132. Green-smut, 301. Guava, 146. Guignardia, 110. aesculi, 390. bidwellii, 120, 439. vaccinii, 110. Gummosis, 74, 141. Gymnoconia interstitialis, 104. Gymnosporangium, 39, 67, 369, 376, 383, 423. clavipes, 69. Gypsophila, 407. Hackberry, 379, 380, 381. Hairy-root, 26, 87, 162. Halo-blight, 299. Hard-rot, 423. Hawthorn, 379, 407, 423. Hazel, 369, 380, 389. Head-smut, 286, 309. Heart-rot, 361, 364, 389, 402. Hedera. 425. Helianthus, 407. Helicosporium nymphsearum, 439. Helminthosporium, 282, 317, 402. carpophilum, 95. inconspicuum, 294, 300. teres, 283. 498 Index Hemileia vastatrix, 144. Hemlock, 365, 367, 368, 369, 371, 373, 379, 380. Hemlock, western, 389. Hemp, 163, 353. Hendersonia, 145, 380. Hepatica, 96, 423. Herpotrichia, 380. Heterosporium, 425. echinulatum, 416. variable, 243. Hibiscus, 23, 407, 423. sabdariffa, 241. Hickory, 359, 367, 380, 381. Historical, 1. concerning prevention, 3. important events, 8. Holcus, 277, 278. Hollow-heart, 235. Hollow-stem, 265. Hollyhock, 10, 24, 423. Honey-locust, 381. Honeysuckle, 88, 407, 408. Hop, 87, 163, 195. Hordeum, 277, 278. Hornbeam, 359, 381. Horse-chestnut, 364, 367, 368, 369, 380, 381, 390. Horse-radish, 195. Hot-water treatment, 271, 274. Huckleberry, 110, 113. Hydnum, 367. erinaceus, 361. Hydrangea, 23, 425. Hydrastis, 195. Hymenochsete, 402. Hypertrophy, 112. Hypochnose, 47, 69, 73. Hypoderma, 380, 397. Hystrix, 277. Iberis, 407, Illosporium, 47. Impatiens, 407. Incense cedar, 369, 380. Inga, 380. Injury to seed by treatment, 277. Insecticide, 449. Internal brown-spot, 236. Inverted-pan method, 461. Irpex, 67, 402. Isariopsis griseola, 159. Ivy, 425. Japan clover, 337. Java black-rot, 420. Java drv-rot, 250. Jelly end-rot, 230. Jerusalem artichoke, 435. Johnson grass, 339. Jonathan-spot, 54. Juniper, 367, 368, 369, 380, 381. Juniperus, 40, 69, 383. Kafir, 307. Kale, 163, 165. Kalmia angustifolia, 113. Keithia, 380. Kernel-smut, 283, 308. Kernel-spot, 395. Knapsack sprayer, 454. Knot, 147, 427. (See also root-knot.) Kochia, 407. Koeleria, 277, 278. Kohl-rabi, 163, 165. Kuehneola albida, 105. gossypii, 349. Labrella pomi, 56. Lsestadia, 251. Larch, 367, 368, 369, 371, 373, 380, 390. Large leaf-spot, 388. Larkspur, 407, 426. Lasiodiplodia triflorge, 99. Late-blight, 174, 217, 263. Late-rust, 105. Lathryus, 407. Laurel, 425. Lavatera, 407. Leaf-anthracnose, 194. Leaf-blight, 68, 70, 134, 183. 187, 195, 244, 250, 348, 398, 402, 425. Leaf-blotch, 159, 234, 390. Leaf-cast, 397. Leaf-curl, 233, 394. Leaf-glaze, 191. Leaf-mold, 262, 416. Leaf -perforation, 199. Leaf-roll, 233, 265. Leaf-rot, 145. Leaf-scorch, 164. Index 499 Leaf-spot, 47, 68, 75, 98, 104, 114, 119, 134, 135, 144, 145, 146, 147, 159, 165, 173, 176, 178, 185, 190, 191, 192, 195, 196, 201, 214, 217, 241, 243, 244, 245, 251, 257, 262, 295, 298, 321, 331, 335, 338, 339, 379, 382, 388, 391, 392, 405, 411, 413, 415, 418, 420, 421, 422, 424, 425, 426, 427, 428, 429, 433, 434, 435, 439. Leak, 134, 234, 264. Leather-leaf, 113. Legumes, 23, 24, 321. Lentil, 163. Lentinus, 367. Lenzites, 367. Leopard-spot, 152, Leptospharia coniothyrium, 105. leaf-blight, 319. saeehari, 245. tritici, 319. Leptostroma, 380. Leptothyrium pomi, 380. Lespedeza, 337. Lettuce, 25, 27, 88, 196. Libertella, 146. Libocedrus, 369. Lichens, 144. Ligu strum, 407. Lilac, 426. Lily, 426. Lily-of-the-valley, 426. Limb-blight, 146. Lime, 23. Lime-sulfur, 443. Lime-sulfur injury, 451. Lime-sulfur wash, 445. Linaria, 407. Linden, 23, 364, 368, 369, 379, 380, 381, 391. Linum, 407. Little-peach, 95. Lobelia, 407. Locust, 23. 361, 367, 368, 371, 379, 380, 381, 391. Lolium, 277, 278. Lonicera, 408. Loose-smut, 280, 296, 315. Lophodermium, 380. brachysporum, 398. Loquat, 147. Lupine, 163. Lychnis, 407. Lythrum, 407. Macrophoma, 113, 146. tumefaciens, 402. Macrosporium, 216, 304, 380. herculeum, 196. leaf-spot, 173. parasiticum, 210. porri, 210. sarcinaeforme, 331. Magnolia, 369, 379. Malnutrition, 173. Mangels, 159. Mango, 147. Mangold, 159. Maple, 23, 359, 361, 364, 365, 367, 368, 369, 371, 379, 380, 381, 392. Marasmius, 251. saeehari, 245. Marigold, 88. Marssonina, 380, 382, 403, 405. ochroleuca, 388. panattoniana, 199. populi, 402. Matthiola, 407. Medlar, 73. Melampsora, 401. lini, 352. saliciscaprae, 405. Melampsorella elatina, 390. Melampsoridium betulinae, 382. Melanose, 144. Melaxuma, 404. Melon, 178. Merulius lacrymans, 374. Mesquite, 372. Microsphsera, 394. alni, 394, 426, 435. diffusa, 337. euphorbiae, 241. Mierostroma, 380. juglandis, 395. Mignonette, 426. Migration of diseases, 10. Mildew. (See downy mildew, pow- dery-mildew.) Millet, 295. 500 Index Milo, 307. Mistletoe, 144, 375, 390, 395. Modified hot-water treatment, 272. Mold, 75, 200, 427, 428, 439. (See also gray-mold, sooty-mold, black-mold, blue-mold.) Monilia, 55, 75, 79, 101. Monilochsetes infuscans, 250. Monochetia, 380. desmazierii, 388. Moon-flower, 427. Morning-glory, 23, 427. Mosaic, 159, 186, 217, 233, 258, 265, 350, 435. Mountain-ash, 368, 369, 380, 381. Mountain -laurel, 425. Mulberry, 23, 25, 367, 368, 369, 372, 381, 393. Mushroom, 200. Muskmelon, 23, 25, 26, 178. Mustard, 163. Mycogone perniciosa, 200. Mycosphaerella, 135, 173, 338. citruUina, 190. fragariae, 132. gossypina, 348. grossulariae, 114. leaf-spot, 114. pinodes, 210. rosigena, 433. rubina, 107. sentina, 68. Myxosporium, 56, 369. Nasturtium, 427. Necator decretus, 145. Neck-rot, 206. Necrosis, 129. Nectarines, 90. Nectria, 135, 148, 251, 369, 402. galligena, 55, 72. ipomoeae, 192. Nematode, 24, 26, 146, 159, 162, 169, 191, 193, 195, 200, 213, 217, 251, 259, 265, 320, 348, 421, 435. Neocosmospora, 214. Neofabrea malicorticis. 44. Neopeckia, 380. Net-blotch, 283. Net-necrosis, 236. Nozzles, 458. Nummularia, 369. discreta, 44. Nursery-blight, 395. Nursery stock, 23. Nut-trees, 89. Oak, 359, 361, 362, 364, 365, 367. 368, 369, 371, 372, 379, 380, 381, 394. Oat, 163, 280, 296. CEdema, 265. Oidium, 50, 122, 241, 420, 435, 436. citri-aurantu, 144. mespilinum, 73. Okra, 25, 201. Oleander, 88, 369, 408, 427. Olive, 147, 367, 369. Olpitrichum, 346. Onion, 25, 26, 201. Orange, 367, 368, 369. Orange leaf-rust, 312. Orange-rust, 104. Orchard grass, 280, 339. Orchard trees, 371. Orchids, 427. Ornamental plants, 406, Orobanche, 159, 259. minor, 331. Osage orange, 380, 394. Ozonium, 146, 201, 248, 323. omnivorum, 23, 53, 346, 372. root-rot, 372. Pacific coast canker, 44. Pseonia, 407. Pale-rot, 73. Pale-spot, 173. Palm, 408, 428. Palmetto, 368. Panicularia, 277. Panicum, 338. Pansy, 436. Parsley, 174. Parsnip, 88, 163, 174. Paspalum, 340. Patellina, 134. Pea, 22, 24, 25, 163, 210. Peach, 25, 79, 87, 90, 367, 369. Peacock leaf -spot, 193. Peanut, 23, 214. Pear, 62, 361, 364, 368, 369, 372. Index 501 Pecan, 25, 88, 369, 379, 380. 381, 394. Pecky heart-rot, 35S. Pecky-rot, 384. Pelargonium, 407, 422, Penicillium, 26, 108, 148, 193. (ligitatum, 141. expansum, 51, 250. italicum, 141. Pentstemon, 408. Peony, 24, 88, 428. Pepper, 23, 25, 215. Perforation, 405. Peridermium, 376, 380, 400, 401. Peronoplasmopara cubeasis, 178. Peronospora, 164, 196, 295. effusa, 244. parasitica, 171. schleideni, 203. sparsa, 433. trifoliorum, 327. vicia?, 338. violae, 437. Persimmon, 23. Pestalozzia, 251, 380, 402. funerea, 194. guepini, 413. Petunia, 407, 429. Phalaris, 277. Phallus, 245. Phleospora, 380. Phleum, 277, 278, 341. Phloem-necrosis, 233. Phlox, 407, 408, 429. Pholiota, 367. Phoma, 20, 163, 230, 369, 380, 385. apiicola, 178. betse, 162. cyclamense, 421. cydonise, 72. dahhse, 421. destructive, 263. lingam, 169. persicae, 96. pomi, 57. root-rot, 162. rot, 173. Phomopsis, 158, 250, 432. citri, 144. ka'mise, 425. maH, 57. vexans, 192, 421. Phoradendron, 375, 376. Phragmidium, subcorticum, 432. Phyllachora, 295, 338. pose, 339. trifoiii, 338. Phyllosticta, 217, 298, 369, 380, 390, 439. acericola, 392. althaeina, 424. antirrhini, 434. apii, 178. batatas, 250. carj^ae, 395. catalpse, 382. chenopodii, 244. chrysanthemi, 418. circumscissa, 96. cucurbitacearum, 190. hydrangeae, 425. leaf-spot, 337. maculicola, 422. primulicola, 429. prunicola, 56. pteridis, 422. richardiae, 413. shot-hole, 74, 96. solitaria, 37. straminella, 241. violae, 437. Phymatotrichum omnivorum, 2."^. PhysaUs, 407. Physalospora, 134, 369. cydonise, 42, 69, 72. Physaruni cinereum, 408. Physoderma zeae-maydis, 292. Physopella fici, 145, 394. Phytophthora, 20, 135. cactorum, 57, 194. infestans, 217, 263. omnivorum, 26. phaseoli, 158. terrestria, 143, 265. Pietin, 317. Piggotia, 380. Pine, 11, 22, 117, 365, 367, 368. 369, 371, 373, 380, 381, 395. Pineapple, 148. Pineapple-disease, 245. Pink, 23, 163, 429. Pink-disease, 135. Pink-mold. 395. 502 Index Pink-rot, 49, 69, 210. Pip, 304. Piped rot, 361. Piqueria, 407. Piricularia grisea, 295. oryzae, 300, 339. Pithiness, 178. Plantain, 135. Plasmodiophora brassiese, 168. Plasmopara viticola, 125. Platycodon, 407. Plectodiscella veneta, 102. Plenodomus canker, 57. destruens, 248. fuscomaculans, 57. Pleospora gramineum, 282. pisi, 213. tropoeoli, 427. Pleurotus, 367. Pleuteus, 367. Plum, 87, 88, 90, 96, 97, 98, 367. Poa, 278, 338. Pod black-rot, 135. Pod-blight, 158. Pod-rot, 157. Pod-spot, 152, 201. Podosphsera leucotrichia, 50. oxyacanthae, 51, 77, 91. Pole-rot, 259. Pollen-blight, 395. Polyporus, 361, 367. betulinus, 382. obtusus, 362. pergamenus, 379. roseus, 384. schweinitzii, 371. squamosus, 364. sulphureus, 361. versicolor, 374, 382. Polystictus, 368. Polythrincium, 328. Pomaceous fruits, 31, 368, 369. Poplar, 88, 359, 365, 367, 368, 369, 371, 380, 381, 401. Poria, 368, 402. Portulaca, 407. Potassium sulfide, 448. Potato, 10, 22, 23, 24, 25, 26, 87, 163, 217. Potato spraying, 236. seed disinfection, 240. Potentilla, 407. Powdery gray-rot, 420. Powdery -mildew, 50, 67, 77, 91, 101, 117, 122, 134, 159, 165, 173, 187, 195, 213, 241, 242. 283, 300, 307, 317, 337, 338, 342, 376, 381, 394, 407, 412, 420, 421, 426, 429, 431, 435, 436, 439. Powdery scab, 224. Power sprayer, 456. Prevention of plant diseases, 12, 13. methods, 14. historical, 3, 13. Primrose, 429. Primula, 407. Privet, 408, 430. Proprietary fungicides, 449. Prothallium-blight, 422. Protocoronospora nigricans, 338. Prune, 87. Prunus, 23, 369. Pseudomonas, 199, 294, 408, 422. angulatum, 257. aptatum, 164, 427. avense, 299. campestris, 165. citri, 137. erodii, 422. glycineum, 337. juglandis, 404. lachrymans, 185. maculicolum, 173. malvacearum, 349. medicaginis, 324. phaseoli, 155. pisi, 213. pruni, 74, 79, 90, 101. savastanoi, 147. solanacearum, 159, 174, 192, 230, 253, 260. stewarti, 291. tabacum, 257. translucens, 282, 319. tumefaciens, 87, 104, 350, 369, 420. woodsii, 416. Pseudopeziza medicaginis, 321. ribis, 115. trifolii, 331. Pseudotsuga, 368, 373. Index 503 Puccinia allii, 210. antirrhini, 434. arenarise, 429. asparagi, 149. bullata, 178. cannae, 413. chrysanthemi, 418. coronata, 278, 298, 339. dispersa, 278, 305. fraxinata, 381. glumarum, 278, 313. graminis, 282, 310, 339, 411. agrostis, 278, 340. airae, 278. avenae, 277, 298. phleipratensis, 278, 341. pose, 278. secalis, 277, 305. tritici, 277. tritici-compacti, 278. helianthi, 435. malvacearum, 423. menthse, 411. poarum, 338. porri, 210. pringsheimiana, 119. purpurea, 278. simplex, 278, 282. sorghi, 294. tragopogonis, 242. triticina, 278, 312. vincse, 436. violse, 437. Puccinastrum hydrangese, 425. Pumpkin, 22, 24, 178. Punica, 407. Pustular-spot, 95. Pyrenopeziza medicaginis, 322. Pyrethrum, 88, 407. Pythiacystis citriophthora, 13-5. Pythium, 163, 376. debaryanum, 193, 234, 328, .349. Quackgrass, 340. Quercus, 363. Quince, 23, 69, 88, 369. Radish, 22, 88, 163, 165. Ramularia, 132, 194, 380. armoracise, 196. primulae, 429. Rape, 163, 165. Raspberry, 22, 87, 88, 102. Rathay's disease, 339. Ray-blight, 419. Razoumofskya, 375, 376, 390. Red-brown root-rot, 371. Red-brown rot, 365. Red-bud, 379. Red cedar, 40. Red heart-rot, 358, 361. Red-leaf, 69. Red leaf-bhght, 350. Red-rot, 214, 244, 371, 384, 401. Red-rust, 251. Redtop, 280, 340. Reseda, 407. Rhabdospora, 145. Rhamnus cathartica, 298. lanceolatus, 298. Rheosporangium aphanidermaius, 163. Rhino trichum, 346. Rhizina, 373. Rhizoctonia, 21, 178, 225, 328, 33 349. crocorum, 327. leaf-blight, 146. Rhizopus, 57. nigricans, 134, 191, 234, 245, 264. Rhododendron, 408. viscosum, 113. Rhubarb, 22, 23, 241. Rhytisma, 380. acerinum, 392. punctatum, 392. Rice, 300. Richardia, 407. Ricinus, 407. Rind-disease, 245. Ring-spot, 173, 245. Ripe-rot, 146. Roestelia, 39, 67, 69. Root-knot, 24, 146, 159, 162, 169, 191, 193, 195, 200, 213, 217, 251, 259, 265, 335, 348. Root-rot, 21, 23, 24, 51, 117, 119, 130, 143, 145, 146, 162, 191, 196, 213, 245, 248, 289, 325, 327, 331, 337, 370, 402, 405, 408, 421, 435, 437, 439. Root-tumor, 164. ,, N f.04 Index Rose, 24, 87, 367, 407, 408, 430. Rose-of-Sharon, 423. Roselle, 94, 241, 265. Rosette, 57, 101, 198, 395. Rot, 111, 135, 148. 194, 365, 417, 420. (See also boll-rot, brown- rot, blossom-rot, gray-rot, soft- rot, root-rot, ripe-rot, bitter- rot, black-rot, pink-rot, red- rot, pod-rot, white-rot, stem- rot, wood-rot, root-rot, timber- rot.) Rotten-neck, 300. Rough -bark, 57. Rubber, 402. Rust, 39, 67, 69, 74, 79, 96, 101, 116, 144, 145, 149, 154, 164, 178, 196, 210, 213, 214, 242, 251, 275, 282, 294, 304, 328, 329, 338, 341, 349, 352, 380, 381, 382, 383, 390, 394, 400, 401, 405, 409, 410, 411, 413, 414, 418, 420, 423, 425, 427, 428, 429, 432, 434, 435, 436, 437. (See also black-rust, blister- rust, black-stem-rust, white- rust, late-rust, orange-rust, yellow-rust.) Rutaba