m UNITED STATES DEPARTMENT OF AGRICULTURE Washington, D. C. PROFESSIONAL PAPER December 10, 1917 WALNUT BLIGHT IN THE EASTERN UNITED STATES. By S. M. ^loMuBRAN, Assistant Pathologist, Office of Fruit-Disease Investigations. CONTENTS. Page. Importance of the disease 1 History of walnut blight 2 The disease in the Eastern State;;... 4 Page. Time of infection 5 Control of walnut blight , 5 Summary,...,.,,,.... 6 IMPORTANCE OF THE DISEASE. The growing of the Persian (English) walnut in the eastern half of the United States is receiving increasing attention and arousing the interest of many. Persian walnut trees, mainly seedlings, either isolated or in small groups or orchards, are by no means uncommon in the States east of Lake Michigan and the Wabash River below the latitude of New England. An indication of the number of such trees now growing in this part of the country was contained in an address by Prof. F. N. Fagan, of State College, Pa., delivered before the Northern Nut Growers' Association in 1915, in which the statement was made that as the result of a recent survey by that college the "location of some 1,500 or 2,000 bearing trees'' had been ascertained in that State. While there has been no effort to make a similar survey in other Eastern States, so far as the writer is informed, his personal knowledge and that of associates in the Bureau of Plant Industry indicates practically the same proportion of Persian walnut trees in the States of New York, Delaware, New Jersey, and Mary- land. Isolated trees are known in lower Connecticut, southern Michi- gan, Ohio, and Virginia. Several eastern nurseries are now spe Note. — This bulletin is intended particuiarly for all engaged in propagating Per walnuts In those portions of the United States east of the Eocky Mountains. Ifi' of scientific interest to plant pathologists. 13187''--17— BuU. Gil ^'o^ograph at various points in the East. The twig-blight form of this disease is also prevalent in various States. The walnut blight, or bacteriosis, is therefore to be figured with in planting the Persian walnut in the East. ... It occurs in Texas and Louisiana, and I think we have it in or near Buffalo, N. Y., and in New Jersey, so if I were 1 Smith, E. F. Bacteria in Relation to Plant Diseases, v. 1, p. 171. Washington, D. C. (Carnegie Inst., Washington, Pub. 27.) ^SmJth, R. E., Smith, C. 0., and Ramsey, H. J. Walnut culture in California. Walnut blight Cal. Agr. Exp. Sta. Bui. 231, p. 113-.S98, 90 fig. 1912. 8 Smith, R. E., Smith, C. O., and Ramsey, H. J, Op. cit. ' * Waitei M. B. The diseases of nut trees. In Rept. Proc. 4th Ann. Meeting, Northern Nut Growers' Assoc, 1913, p. 56. 1914. 4 BULLETIN 611, U. 3. DEPABTMENT OF AGRICULTURE. planting extensively I should expect that disease to be serious. That would be ray forecast of the matter. The humidity and cloudy weather in the East ought to be moi-e fsivorable to the disease than the climnte of California. There is no reason to suppose that blight will not appear wherever Persian walnuts are grown. THE DISEASE IN THE EASTERN STATES. During the first week in June, 1916, a trip was made by the writer to various points in Delaware, New Jersey, and Pennsylvania where bearing walnut trees were known to be located. On practically every tree that had a crop the nuts were found to be spotted in a manner very characteristic of bacteriosis (PL I). The lesions at this time were small and superficial in character, rarely extending more than 2 to 3 millimeters (about one-tenth of an inch) into the husk. A number of specimens were collected and cultures obtained. The technique used consisted in washing the nuts with soap and water, sterilizing the surface with an alcoholic solution of mercury bichlorid for five minutes, and then washing in distilled water. After this treatment the epidermis of the diseased spots was removed carefully with a sterile scalpel and bits of subepidermal tissue trans- ferred to tubes of melted beef agar, agitated, further diluted in a second and third tube of the same media, and poured into Petri dishes. About 15 attempts were made, in practically all of which bacterial colonies of a similar type appeared on the plates in from two to four days, and the plates from the third dilutions usually contained colonies which were so few as to allow transfers to be made to tubes without difficulty. During the first week in August a series of inoculations was made on the nuts and twigs of a certain mature tree at Lancaster, Pa., which was said to be a seedling of Rush. The husks of 24 young nuts entirely free from any trace of the disease were inoculated (1) by spraying with a suspension of the germs in rain water, (2) by smearing on the culture, and (3) by puncturing with an infected needle. Several untreated nuts were tagged as controls. At the same time five young, tender, growing twigs .5 to 10 millimeters in diameter were inoculated with the germs about 6 inches from the tips by making several punctures in each with an infected needle ; one twig was punctured with a sterile needle as a control. The organisms used in these experiments were all from pure cultures on beef agar and obtained as previously described. A month later (Sept. 5, 1916) it was found that 21 of the 24 nuts inoculated had developed the disease and 3 showed no trace of it; the untreated nuts were perfectly clean. Of the five twigs inocu- lated, all had developed cankers from 5 to 10 mm, in length and from 2 to 5 mm. in width. Plate II shows one of the nuts 30 days after Bui, 61 1, U. S. Dept. of Agriculture. Plate I. Bui. 61 1, U. S. Dept. of Agriculture. Plate II. Diseased and Healthy Persian Walnut Twigs and a Nut Affected with Walnut Blight. A nnd n typical cjukers produced on twigs in one mouth's time by needle punctures from pure culture; C, a control twig punctured with a sterile needle; D, a diseased nut one monlh alter being inoculated from a pure culture by a needle puncture. WALNUT BLIGHT IN THE EASTERN UNITED STATES. 5 inoculation b)^ needle puncture and two inoculated twigs having characteristic cankers. The control, which was punctured with a sterile needle, is shown at the right. The needle punctures in the con- trol barely showed at this time, 30 days after inoculation. Subsequently the organism was reisolated from a number of these inoculated nuts, and the cultural studies so far made from these isolations coincide with those made by Smith ^ and by Pierce.* TIME OF INFECTION. During the season of 1916 infection apparently took place about the last of May in the cases under observation. At this time the nuts were very well developed, approximately three-fourths to 1 inch in diameter, and although there was a slow increase in the area of the infection points through July and some coalescing of these spots to form larger ones, the disease did not begin to work deeply into the tissues until about the middle of August, by which time the shell had formed and hardened. By the end of the season the husks had become black, watery, and rotten, staining the shells and clinging to them when allowed to dry. The develop- ment of the nuts did not seem to be affected materially, if at all. The growers interviewed were unanimous in stating that infection was usually late and that no material shortage of crop resulted there- from. However, the former part of this statement probably could be applied only to the time at which the infection became so evident as to attract the attention of ordinary observers. In the California orchards the greatest loss from infection occurs at or near blooming time. Infection is serious in proportion as the weather is moist at that time. A dry, clear spring means little, if any, blight, whereas serious infection is associated with moist, foggy spring weather. The disease as observed in 1916 in Pennsylvania, Delaware, and the District of Columbia resembled closely the severe late infections described by Smith.^ CONTROL OF WALNUT BLIGHT. Various attempts to control this disease by spraying and by soil applications have been made in California, and although some suc- cess has attended the spraying experiments it has not been of such degree as to extend any material encouragement to the commercial orchardist. That spraying will be of no value under eastern condi- tions can not be assumed from this fact, however, owing to the dif- ference in the infection periods previously referred to. Neverthe- less, spraying to control diseases of bacterial origin has never been * Smith, R. E., Smith, C. 0., and Etamsey, H. J. Op. clt. * Pierce, N. B. Op. cit 6 BtrLLE'rijS' eiiy It. "s. Dfei>ARTM6>f'i' of AGRICULTDRE. §b successful as in the control of those due to fungi; until the efficacy Hi spraying may have become established, too much should not be expected from this method of control. A logical and seemingly practicable method of avoiding losses inci- dent to bacteriosis isin the possible development of immune or highly tesistant varieties. Work along this line is now under way on the Pacific coast, but it is not known that any varieties altogether re- sistant to blight or even practically immune to it have thus far been brought to light. However, among the many thousands of seedling trees on the Pacific coast and the hundreds in the eastern United States, it would not seem too much to presume that for general orchard planting blight-resistant and otherwise desirable varieties will yet be found. Whenever such varieties are discovered, arrange- ments maj^ be made with the Department of Agriculture for testing their susceptibility to this disease by means of inoculation experi- ments. Meanwhile, it is to be hoped that the planting of small com- mercial orchards and of trees for home use will be continued, as small groups of bearing trees over a wide range of territory will furnish valuable suggestions as to future commercial plantings. SUMMARY. ' Walnut blight, or bacteriosis, is distributed very generally through- but the eastern half of the country. Investigations by Mr. M. B. Waite and the writer have demonstrated its occurrence in Louisiana, the District of Columbia, Maryland, Delaware, Pennsylvania, and 'New York, and there seems to be no reason to suppose that it will not occur wherever Persian wailnuts are grown in the United States. During the summer of 1916 pure cultures of the causal organism •were obtained from naturally infected nuts; inoculation experiments ,were conducted in healthy tints and twigs, and these inoculations were uniformly successful in producing the disease. Cultural studies were conducted in the laboratory, and the results obtained corresponded with those reported by Pierce^ and by Smith.^ The writer's observations of this disease have covered one season only, and therefore definite conclusions as to its behavior under vary- ing seasonal conditions are not possible. It may be stated, however, that late infections were the rule during the season of 1916, and if this condition holds generally true from season to season it will con- stitute a striking difference between the behavior of the disease in the Middle Atlantic States and on the Pacific coast. Extensive experiments to control this disease by spraying have been conducted from time to tiipe in California, but the results ob- tained have never been entirely satisfactory. Here, again, the differ- * Pierce, N. B. Op. cit 'Smith, R. R, Smith, C. O.. and Ramsey, H. J. Op. cit WALNUT BLIGHT IN THE EASTERN UNITED STATES. 7 f «nce in infection periods may alter results, but from the best infor- mation at present available it appears that the solution of the problem of the control of this disease rests in the development of immune or highly resistant varieties. Nurserymen and growers should be on the watch for such sorts as combine a high resistance to this disease with the other qualities necessary in a good commercial nut, and whenever such varieties are found they should be propagated. The wide planting of small lots of trees will furnish in the course of a few years valuable suggestions as to the requirements and range of the Persian walnut in the Eastern States, and should not be dis- couraged on account of blight. Although it is not possible at this time to say that this nut has large commercial possibilities in the section east of the Rocky Mountains, it is equally impossible to state, the contrary as the fact. It is well established, however, that there are now hundreds of seedling trees in New York, Pennsylvania, New Jersey, Delaware, and Maryland bearing nuts of more or less merit despite the presence of this disease, and apparently there is no reason why every farm and country home in this district should not have a small planting of these productive as well as highly ornamental trees. \ LIBRftRY OF CONGRESS 002 813 193 8 PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF AGRI- CULTURE RELATING TO THE SUBJECT OF THIS BULLETIN. AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT. The San Jose Scale and Its Control. (Farmers' Bulletin 650.) The Apple-Tree Tent Caterpillar. (Farmers' Bulletin 062.) Pecan Culture; with Special Reference to Propagation and Varieties. (Farmers' Bulletin 700.) The Bagworm, an Injurious Shade-Tree Insect, (Farmers' Bulletin 701.) The Leopard Moth : A Dangerous Imported Insect Enemy of Shade Treesk (Farmers' Bulletin 708.) The Leaf Blister Mite of Pear and Apple. (Farmers' Bulletin 722.) The Oyster-Shell Scale and the Scurfy Scale. (Farmers' Bulletin 723.) The White-Pine Blister Rust. (Farmers' Bulletin 742.) Orchard Barkbeetles and Pinhole Borers, and How to Control Them. (Farmers' I Bulletin 763.) The Death of Chestnuts and Oaks Due to Armillaria Mellea. (Department! Bulletin 89.) Walnut Aphides in California. (Department Bulletin 100.) Endothia Parasitica and Related Species. (Department Bulletin 380.) The Chestnut Bark Disease. (Separate 598 from the Yearbook of 1912.) FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTIN&J OFFICE, WASHINGTON, D. C. Scale Insects and Mites on Citrus Trees. (Farmers' Bulletin 172.) Price 5J cents. The Control of the Chestnut Bark Disease. (Farmers' Bulletin 467.) Price I 5 cents. The Antliracnose of the Mango in Florida. (Department Bulletin 52.) Price! 10 cents. A Disease of Pines Caused by Cronartium Pyriforme. (Department Bulletin) 247.) Price 5 cents. Apple Leaf-Spot Caused by Sphaeropsis Malorum. try Bulletin 121.) Price 5 cents. The Present Status of the Chestnut-Bark Disease, try Bulletin 141.) Price 5 cents. The Persian Walnut Industry of the United States. Bulletin 254.) Price 20 cents. Cultural Characters of the Chestnut-Blight Fungus and Its Near Relatives. (In Bureau of Plant Industry Circular 131.) Price 5 cents. Diseases of Ornamental Trees. (Separate 463 from the Yearbook of 1907.) | Price 5 cents. 8 (In Bureau of Plant Indus- 1 (In Bureau of Plant Indus-] (Bureau of Plant Industry I ADDITIONAL COPIES THIS PUBLICATION MAY BE PROCXTREt) FROM THE SUPERINTENDENT OF DOCirMKNTS GOVERNMENT PRINTING OFFICB ■WASHINQTON, D. C. AT I CENTS PER COPY