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Verticillium Wilt in Alfalfa. A. A. Christen, Research Associate, Department of Plant Pathology, Washington State University, WA 99350. R. N. Peaden, Research Agronomist, AR, SEA, USDA, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. Plant Dis. 65:319-321. . This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/PD-65-319.

Verticillium wilt of alfalfa, caused by Verticillium albo-atrum, is extensively distributed in the Pacific Northwest. Diseased alfalfa occurs on humid coastal acid soils of Washington and Oregon. It is common in irrigated neutral to alkaline soils of the Columbia Basin of Washington, north-central and eastern Oregon, southwestern Idaho, and southern British Columbia, Canada. The disease was absent in dryland fields, even those adjacent to irrigated fields. Field symptoms, which are distinct when plants are in the early bud stage, typically consist of V-shaped pinkish orange brown necrotic areas on the leaflets. Leaflets on severely affected shoots are usually necrotic and twisted, forming spirals. Diseased stems remain erect but do not become chlorotic until all leaves have lost chlorophyll. New shoots on infected plants appear normal at first but show typical symptoms as they approach physiologic maturity. Symptoms were produced in controlled temperature chambers at 1527 C. Isolates grown in the laboratory produced dark resting mycelia. Dimensions of conidia and conidiophores correspond with those described for V. albo-atrum. Thirty-eight geographic isolates produced similar symptoms and death in susceptible alfalfa plants.