BLIGHTS of LILIES and TULIPS 6Ll Transmit Them, Their Host Range, and Varietal Reactions
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BLIGHTS OF LILIES AND TULIPS 6ll transmit them, their host range, and varietal reactions. Until more detailed knowledge is available there is little basis for suggesting a sound program of control. Dr. Magie, in the North American Blights of Gladiolus Council Bulletin No. 20, December 1949, suggested the value of certifying planting stock of gladiolus, Lilies and comparable to the program of certify- ing white potatoes. The stocks, he wrote, might be "produced in parts Tulips of the country where disease spread is naturally light or absent." He was concerned mainly with fusarium rot C. J. Gould control, but he also mentioned virus control. Such a program would be Whether one grows tulips or lilies good if it could be put into practice. for fun or for profit—in Brooklyn, But no one knows now which areas are Keokuk, or Seattle; in the garden, favored by light spread of gladiolus field, or greenhouse—he probably has viruses; more research is necessary more grief from botrytis blights than before the gladiolus industry can fol- from any other cause. low the path of the potato industry; The blights, or "fire" as they are and the number of gladiolus varieties sometimes called, are world-wide in in the trade, already enormous, is con- distribution and most prevalent in tinually augmented by the new pro- cool, moist areas. They are caused by ductions of hundreds of amateur similar, but distinct, fungi. Most com- breeders. Therefore we find less inter- mon on tulips is Botrytis tulipae. Most est in protecting the present commer- common on lilies is Botrytis el lip tica. cial varieties than in developing new Tulip blight begins with a diseased sorts. Of course the situation would bulb or with contaminated soil in improve if breeders of gladiolus w^ould which the fungus is living on old re- take all possible care to avoid exposing mains of the tulip plant. As the young their seedlings to sources of infection tulip shoot pushes through the ground, so that only disease-free new varieties it becomes infected if it comes in con- might enter the trade. tact with the fungus and may be changed into a distorted, grayish- PHILIP BRIERLEY, a senior pathologist brown body covered with powdery in the Bureau of Plant Industry^ Soils, and masses of spores. Sometimes only part Agricultural Engineering, has been em- of a leaf is diseased. Often the entire ployed by the Department of Agriculture shoot is affected. Soon the leaves of the since ig22. nearby tulip plants become spotted FLOYD F. SMITH is a senior entomolo- with small, circular, yellow or brown gist in the Bureau of Entomology and dots. Many of the spots remain small Plant Quarantine. For many years he has and dry up, but others, (especially if done research on insects that affect green- the weather is cool and moist) enlarge house and ornamental plaîiis. He holds rapidly. Their color becomes a gray- degrees from Ohio State University, ish brown or brown, with a dark water- FRANK P. MGWHORTER in igjo en- soaked margin. Powdery masses of tered cooperative employment by the Oregon spores often form in the center. Agricultural Experiment Station and the These, when blown to other plants, United States Department of Agriculture. initiate more spots, which may become Since then he has specialised in virus dis- visible within 24 hours. eases of bulb and legume crops. Large spots near the leaf base often 6l2 YEARBOOK OF AGRICULTURE 1953 cause the leaf to break. Several spots under certain conditions according to may fuse and decay a leaf completely» tests by Neil A. MacLean at Washing- Spots on stems are similar and may ton State College. Other species of also cause the stems to break. Flowers Botrytis, including B. cinérea^ can some- are very susceptible and often are times attack tulips. made unsalable by white or brown Although B. tulipae can attack spots covered with spores. Not even healthy leaves, its entrance is facili- the bulb escapes. On its outer fleshy tated by injuries from frost, hail, and scale the fungus may produce sunken, equipment. The Dutch have tried to yellow or brown craters. In them, on reduce frost injury by treating the the outer bulb husk, and on spots on bulbs to delay growth in the spring the upper plant parts, small, hard, until the danger is partly over. This black circular masses of the fungus artificial retarding is accomplished by may develop. Such black bodies, the storing the bulbs at approximately 70^ sclerotia, have a function somewhat F. and delaying planting until October similar to seeds in that they enable the or November. fungus to live over winter, either on Much can be done to control the the bulb or on dead tulip parts. Then, disease in commercial fields and home when infection from the sclerotia occurs gardens by proper cultural practices: in the spring, the cycle is continued by Digging every year; not replanting the spores. tulips in the same location for at least The disease probably occurs wher- 3 years; planting so as to provide good ever tulips are grown, but it is most air circulation and low humidity by serious when conditions are cool and proper selection of site, proper spacing, moist. Consequently it is prevalent and thorough weeding; removing in the Netherlands, southwestern promptly and destroying diseased England, and the Pacific Northwest. shoots, old and infected flowers, and Local conditions, however, arc im- dead plant remains; and planting only portant: In western Washington, for healthy bulbs. example, the disease is more serious in Since the original infections arise the valleys near Puyallup than it is from diseased bulbs that escape de- go miles to the north near Mount tection, it would seem logical to treat Vernon, where the plants are exposed them with a fungicide in order to to a more or less constant wind from destroy the fungus. Many treatments Puget Sound. have been tested and a few have been The method of planting tulips com- recommended, such as Uspulun and mercially in beds about 3 feet wide, as Aretan, in Europe. Such treatments practiced in Holland and some parts have not met with general success, of the United States, is more conducive however. Either they injured the bulbs to botrytis blight than is the row system or failed to control the disease ade- used in the Pacific Northwest. Not only quately. is the relative humidity higher in the Early attempts to prevent plants beds, but there is also a greater oppor- from becoming diseased by using tunity for infection. Likewise the dis- fungicidal sprays were likewise not ease is often found in gardens in massed very successful. Although copper- plantings or on plants in shaded places. containing compounds such as bor- Most, if not all, tulip varieties are deaux mixture were found capable of susceptible, but there is some variation. controlling the fungus, they often Among varieties that are very suscept- caused considerable injury to the ible are the popular William Copland, leaves and flowers. However, in New William Pitt, and Bartigon. Baronne York in 1940 L. W. Nielson and C. E. de la Tonnaye is supposed to be resis- Williamson found that silver nitrate tant. This species of Botrytis can also sprays compared favorably with the attack bulbous plants other than tulips 1.5-4.5-50 bordeaux mixture in fun- BLIGHTS OF LILIES AND TULIPS 613 gicidal action. One spray, contain- the soil level and so injure them that iag silver nitrate, manganese sulfate, the foliage above turns yellow. and hydrated lime was adopted by Spots on the flowers usually are bulb growers on Long Island. brown and in cool, moist weather Meanwhile tests in 1938 in the Neth- rapidly convert the flowers into wet, erlands had shown promising results slimy masses covered with powdery with thiram, one of the new organic- layers of spores. In warm, dry weather sulfur compounds. I tested it and the spots on leaves and flowers stop related sulfur com^pounds in compar- enlarging and dry up. With ample ison with silver and copper fungicides moisture and an optimum tempera- at the Western Washington Agricul- ture near 60^ F., however, a new spot tural Experiment Station beginning may develop within 24 hours and new in 1942. Then and later the best re- spores within a few days thereafter. sults were had with ferbam, another Given suitable moisture and temper- organic sulfur compound. Large-scale ature conditions, the cycle may repeat tests by growers in 1943 corroborated itself every few days throughout the the experimental trials. Afterwards it growing season. Meanwhile, hardened came into general use in the Pacific masses of the fungus are forming in Northwest and the Netherlands. the diseased portions. These masses, Four applications of ferbam are usu- the sclerotia, are first white and later ally enough in the Northwest, begin- black. They may be rounded, elliptical ning when the shoots are 2 to 4 inches or irregular, and one-thirty-second to tall and continuing at 7- to lo-day one-quarter inch in size. Under favor- intervals. The spraying must be ac- able conditions the sclerotia germinate companied by the prompt removal of the following spring to produce spores. infected plants as soon as detected. The fungus overwinters in at least By combining the proper cultural three ways: It can survive in the form practices and a spraying program, the of sclerotia. It can live saprophytically disease can now be conquered. in lily debris. It can survive in the basal rosettes of leaves of such lilies BOTRYTIS BLIGHT OF LILIES, like tulip as the Madonna lily.