BIOLOGICAL-CONTROL OF RHIZOCTONIA-SOLANI ON TALL FESCUE USING FUNGAL ANTAGONISTS

A binucleate Rhizoctonia sp. (isolate GM 460) from soil and Gliocladiu m virens (isolate TRBG) from creeping bentgrass consistently inhibited Rhizoctonia blight on tall fescue in laboratory bioassays. When R. so lani was inoculated onto tall fescue seedlings treated with either ant agonist, 20-60% of the foliage was blighted after 10 days, whereas 80- 100% of the foliage was affected in the controls. Suppression of bligh t was associated with reduced growth of R. solani on grass blades. GM 460 and TRBG differed in their tolerance of decreasing relative humidi ty. At 100% relative humidity, TRBG grew on grass blades to a greater extent than GM 460; at 95% relative humidity, GM 460 grew on grass bla des but TRBG did not. When tall fescue seedlings treated with the fung i were subjected to 35-45% relative humidity for 3 days before being i noculated with the pathogen at greater than 95% relative humidity, TRB G did not inhibit the disease, whereas GM 460 was suppressive. A combi nation of GM 460 and TRBG was as or more effective than the individual isolates, but combinations of either fungus with other fungal isolate s often resulted in decreased efficacy. When GM 460 was applied to tal l fescue in the field, it persisted on treated turf for a 1-mo period and reduced brown patch development from 35% blighted turf in the cont rol to less than 20%. Applications of GM 460 or TRBG in a subsequent f ield experiment, however, were ineffective. The only effective treatme nt in this experiment was a combination of GM 460 and TRBG, which decr eased the percent blighted turf from the 30-36% in the controls to 14- 26%.