Rhizoctonia Root Rot of Small Grains Favored by Reduced Tillage in the Pacific Northwest

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Abstract
Rhizoctonia root rot of wheat and barley casued by Rhizoctonia solani and responsible for bare patch in the field was identified in the United States for the first time. The disease was recognized at six sites; a research winter wheat plot and a commercial field of spring barley in Oregon, a commercial field of spring barley and research spring wheat plots in Washington, and a commercial field of durum wheat and one of winter wheat in Idaho. Diseased plants were severely stunted and occurred in distinct patches of various sizes. Seminal and crown roots of diseased plants had distinct brown sunken lesions and "pinched-off" pointed tips, symptoms previously reported as characteristic of Rhizoctonia root rot. Isolates of R. solani recovered from diseased tissue were multinucleate and produced identical root symptoms in greenhouse tests. At all sites where the disease occurred, the wheat or barley was either direct-drilled (no-tillage) into stubble, sown with minimal prior tilage, or sown the same day the soil was tilled. In experimental plots with winter wheat, there were 9.9, 2.8 and 1.4 patches per treatment (130 m2) in which no-tillage, reduced tillage, and conventional tillage, respectively, were practiced.