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Influence of Glyphosate on Rhizoctonia Root Rot, Growth, and Yield of Barley. Richard W. Smiley, Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton, OR 97801. Alex G. Ogg, Jr., and R. James Cook. Agricultural Research Service, U.S. Department of Agriculture, 367 Johnson Hall, Washington State University, Pullman 99164. Plant Dis. 76:937-942. Accepted for publication 14 April 1992. 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, 1992. DOI: 10.1094/PD-76-0937.

Time intervals between applying glyphosate to kill volunteer cereals and weeds and planting spring barley by direct drilling (no-till) into Rhizoctonia-infested soil were evaluated in field plots at Pendleton, Oregon, and Lacrosse and Lind, Washington. As the interval was shortened from autumn to spring application or from 3 wk to 3 days before planting in the spring, severity of Rhizoctonia root rot increased and grain yield decreased. When glyphosate applications were delayed until 2 or 3 days before planting (commonly used in production of spring barley in the Pacific Northwest), spring barley yields were reduced as much as 50% compared to when glyphosate was applied in the autumn or early spring. Disease was not as prevalent when glyphosate was applied 1 or 2 days after direct drilling compared with applications made 3 days before planting. Rhizoctonia root rot was least on spring barley when tillage or application of glyphosate was performed in the autumn or in spring 3 wk before planting. Tilling soil 2 days before planting at one site nullified the yield-depressing effect of a preplant glyphosate application. These results suggest that the inoculum potential for R. solani AG-8 as a pathogen of spring barley is strongly influenced by the timing of volunteer cereal and weed elimination and that adjustments in such practices can minimize crop damage and maximize yield.