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Effect of Fungicides Applied Singly and in Combination on Seed Yield and Three Leaf Spot Diseases in Orchardgrass. Ronald E. Welty, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, National Forage Seed Production Research Center, 3450 S.W. Campus Way, Oregon State University, Corvallis 97331-7102. Plant Dis. 75:1004-1008. Accepted for publication 18 April 1991. 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, 1991. DOI: 10.1094/PD-75-1004.

Leaf diseases caused by Mastigosporium rubicosum (cause of eyespot), Rhynchosporium orthosporum (cause of scald), and Cercosporidium graminis (cause of leaf streak) were identified on orchardgrass (Dactylis glomerata) grown for seed. Fungicides (captafol, chlorothalonil, and propiconazole) were applied up to three times per year to plants in different stages of growth for 5 yr (19841988). Leaf area damaged by diseases (primarily scald) ranged from moderate to severe depending on the yearly variation in precipitation. In wet years, seed yields were significantly larger (P = 0.05) in plots treated with chlorothalonil than nontreated controls. Scores for leaf area damaged by disease in plots treated with chlorothalonil (when significantly different from controls) were inversely related to seed yield.

Keyword(s): forage, Scolicotrichum graminis, seed production.