A closer look at dollar spot on bentgrass fairways

University of Maryland (UMD) researcher Fereshteh Shahoveisi, Ph.D., tested fungicides in College Park, Md., to manage dollar spot on Penncross creeping bentgrass. Shahoveisi mowed fairway plots three times weekly to a height of 0.5 inches.

She applied treatments on 14-day or 21-day intervals from May 18 to July 20, with a CO2 backpack sprayer at 40 psi. The sprayer had a single Teejet AI9508E nozzle, and the water carrier was equivalent to 1.5 gal per 1000 ft. sq.

Treatment products included Tekken 1.8 SC (isofetamid, PBI-Gordon), Daconil Ultrex 82.5 WDG (chlorothalonil, Syngenta) and the experimental fungicide UMD-DS-B-1 (PBI-Gordon).

Shahoveisi arranged the 3-by-6-foot plots in a randomized complete block design with four replications. She did not have to inoculate the plots since dollar spot occurred naturally. Disease severity assessment was the number of dollar spot infection centers per plot every two weeks from June 1 to August 24.

Shahoveisi used a standardized area under the disease progress curve (SAUDPC) to evaluate disease progress over time. Data was subjected to analysis of variance and means separation using Fisher’s least significant difference (LSD) procedure at α= 0.05.

Dollar spot pressure increased throughout the summer. All treated plots had lower dollar spot severity and SAUDPC values than non-treated plots. Plots treated with UMD-DS-B-1 applied at 3 fl. oz. per 1000 ft. sq. or Tekken applied at 2.8 oz. per 1000 ft. sq. had lower dollar spot severity from June 15 to August 11 than plots treated with Daconil Ultrex alone or with UMD-DS-B-1 at 2 fl. oz. per 1000 ft. sq.

Plots treated with UMD-DS-B-1 (3 fl. oz./1000 ft. sq.) or Tekken alone had lower SAUDPC values than other fungicide treatments. There was no phytotoxicity following fungicide applications. Additional fungicide research conducted at Purdue University on creeping bentgrass putting greens and fairways is featured in the research article by Lee Miller, Ph.D., and Matthew Carpenter, here.