BIOLOGICAL-CONTROL OF DOLLAR SPOT DISEASE OF CREEPING BENTGRASS

Top-dressing creeping bentgrass with sand-cornmeal or chopped grain colonized by fungi or bacteria was tested as a means of suppressing the intensity of epidemics of dollar spot disease incited by Sclerotinia homoeocarpa. In a greenhouse, 45- to 90-day-old turfgrass grown in cups was top-dressed with 1,500 cm3/m2 of sand-cornmeal infested by mycelium of S. homoeocarpa, followed by an equal amount of sand-cornmeal infested by potential antagonists. Four of 24 potential antagonists inhibited the growth of S. homoeocarpa and suppressed disease by 25-90%. In 1987, plots on a closely mown sward of creeping bentgrass were treated with inoculum of S. homoeocarpa and top-dressed weekly with sand-cornmeal (400 cm3/m2) infested by isolates of potential antagonists. Maximum disease intensities (percentage of plot area blighted) were 5, 18, or 44% in plots treated with sand-cornmeal infested by Fusarium heterosporum, an Acremonium sp., or an unidentified bacterium, respectively, during a 35-day epidemic, compared to 84% in plots not top-dressed and 64% in plots top-dressed with noninfested, autoclaved sand-cornmeal. In another experiment, maximum disease intensities were 31% in plots not top-dressed; 9% in plots top-dressed with noninfested, autoclaved chopped grain; or 3-6% in plots top-dressed with chopped grain infested by potential antagonists. In 1988, treatments at 2-wk intervals with sand-cornmeal infested by F. heterosporum (isolate pa 7) at 400 cm3/m2 limited disease intensity of a 78-day epidemic of dollar spot to 3%, compared to 18% in nontreated plots. Sterilization of sand-cornmeal infested by F. heterosporum (isolate pa 7) by heating to 70 C for 1 h did not significantly (P = 0.10) reduce efficacy. Results of laboratory and greenhouse experiments suggest that F. heterosporum (isolate pa 7) produces substances toxic to S. homoeocarpa.