Synergistic Interaction of Fungicides in Mixtures under Different Conditions of Dollar Spot Disease Caused by Sclerotinia homoeocarpa

Dollar spot caused by Sclerotinia homoeocarpa F.T. Benn. is a common and economically important turfgrass disease in South Korea. Fungicides were evaluated for control of dollar spot in creeping bentgrass golf course putting green. Commercial formulations of propiconazole, thiophanate-methyl, chlorothalonil, trifloxystrobin and boscalid were applied to plots of creeping bentgrass, each of the latter four fungicides was tank mixed with propiconazole at the same rates, and applied as treatments. The dollar spot severity in the nontreated plots of field A and B progressed toward peak diseases of 18.3 and 66.7% from 10 or 15 days after inoculation, respectively. Significant differences were detected among control values of the fungicides. Dollar spot control provided by boscalid was significantly greater than the other fungicides which showed low control values in a higher disease condition. No synergistic interactions, except propiconazole + thiophanate-methyl treated plot, were detected under a lower disease pressure. However, under a higher disease pressure, synergism was observed at all fungicide combinations, except a propiconazole and boscalid tank mixture. These data suggest turfgrass managers in golf course can take advantage of fungicide synergism to control dollar spot using the products and rates in this study.