Root Rot Induced in Snap Bean by Rhizoctonia solani AG-4 and AG-2 Type 2 in Conservation Tillage Following Corn. Htay Htay Win, Department of Plant Pathology, University of Georgia Coastal Plain Experiment Station, Tifton 31793-0748. Donald R. Sumner, Department of Plant Pathology, University of Georgia Coastal Plain Experiment Station, Tifton 31793-0748. Plant Dis. 72:1049-1053. Accepted for publication 21 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-1049.

A snap bean double-crop was planted no-till for 3 years following field corn with symptoms of crown and brace root rot induced by Rhizoctonia solani AG-2 type 2, and for 2 years following sweet corn in soil infested with inoculum of R. solani AG-4 and disk harrowed. Yield of green pods from plants grown in soil infested with R. solani AG-2 type 2 was only one-third of the yield from plants grown in noninoculated soil (1,056 vs. 3,185 kg/ha) in the first year, but yields were not different in the other 2 years. Seed and soil fungicide treatments were rarely beneficial in increasing plant stand or yield. In soil infested artificially with a low inoculum density of R. solani AG-4 (3–7 cfu/100 g of oven-dry soil), yield of green pods was consistently 20–30% less than yield in noninoculated soil. Tolclofos-methyl (but not PCNB or metalaxyl) reduced root and hypocotyl disease severity but did not increase yield. Yield of different cultivars varied with different levels of soil infestation with inoculum of R. solani AG-4, but compared with noninoculated soil, yield of all cultivars was low (680–2,360 kg/ha) in infested soil.