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

A binucleate Rhizoctonia sp. (isolate GM 460) from soil and Gliocladium virens (isolate TRBG) from creeping bentgrass consistently inhibited Rhizoctonia blight on tall fescue in laboratory bioassays. When R. solani was inoculated onto tall fescue seedlings treated with either antagonist, 20-60% of the foliage was blighted after 10 days, whereas 80-100% of the foliage was affected in the controls. Suppression of blight was associated with reduced growth of R. solani on grass blades. GM 460 and TRBG differed in their tolerance of decreasing relative humidity. 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 blades but TRBG did not. When tall fescue seedlings treated with the fungi were subjected to 35-45% relative humidity for 3 days before being inoculated with the pathogen at greater than 95% relative humidity, TRBG did not inhibit the disease, whereas GM 460 was suppressive. A combination of GM 460 and TRBG was as or more effective than the individual isolates, but combinations of either fungus with other fungal isolates often resulted in decreased efficacy. When GM 460 was applied to tall 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 control to less than 20%. Applications of GM 460 or TRBG in a subsequent field experiment, however, were ineffective. The only effective treatment in this experiment was a combination of GM 460 and TRBG, which decreased the percent blighted turf from the 30-36% in the controls to 14-26%.