Effects of Cultivars and Cultural Practices on Sclerotinia Stem Rot of Soybean. C. R. Grau, Associate Professor, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706. V. L. Radke, Project Specialist, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706. Plant Dis. 68:56-58. Accepted for publication 27 July 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-56.

Sclerotinia stem rot of soybean was studied in naturally infested field plots at two locations. Soybean cultivars Hodgson and Corsoy were less diseased than Wells, SRF-200, Steele, and Asgrow 2656. Disease severity indices (DSI) (0 = no disease, 100 = 100% death) were greater for all cultivars planted at row widths of 25–38 cm compared with DSI at row widths of 76 cm for 2 of 3 yr. Yields were lower for soybeans grown at row widths of 25–38 cm than for row widths of 76 cm for all years. Disease severity was greater in irrigated plots than in plots that were not irrigated either before or after flowering. Yields were improved 10–22% by reducing disease severity through reduced irrigation before the R1 growth state (early flowering). Although the amount of precipitation and supplemental irrigation influenced disease severity, air temperatures were also associated with disease development.