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Yield Losses in Soybeans Induced by Powdery Mildew. J. M. Dunleavy, Research Plant Pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Professor, Department of Botany and Plant Pathology, Iowa State University, Ames 50011. Plant Dis. 64:291-292. Accepted for publication 29 October 1979. 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, 1980. DOI: 10.1094/PD-64-291.

Soybean yield losses caused by natural infection with Microsphaera diffusa, the powdery mildew fungus, were assessed by testing three susceptible and three resistant cultivars at three locations in Iowa for 3 yr. A spray containing benomyl was applied weekly to plant rows until runoff, from 1 July until near plant maturity. Nonsprayed rows served as controls. Seed yield losses ranged from 0 to 26%; mean seed yield loss for the 3 yr was 13%. Plants of resistant cultivars were not infected by M. diffusa, and seed yield was unaffected by benomyl treatment. Findings indicate that no disease other than powdery mildew reduced the yield in nonsprayed susceptible plants and that benomyl had no phytotoxic or stimulatory effects on resistant plants.