Research Update from UMD

Evaluation of preventative fungicides for the management of dollar spot on fairway height creeping bentgrass, 2022

By Fereshteh Shahoveisi, Ph.D., Department of Plant Sciences and Landscape Architecture, University of Maryland

Fungicides were tested in a field trial conducted at the University of Maryland Paint Branch Turfgrass Facility, in College Park, MD. The efficacy of experimental and registered fungicides in the management of the disease was evaluated on creeping bentgrass cv. Penncross mowed three times a week to golf fairway height (0.5 in.). Treatments were applied on 14 or 21 d intervals from 18 May to 20 Jul with a CO2 backpack sprayer at 40 psi equipped with a single Teejet AI9508E nozzle in water equivalent to 1.5 gal /1000 ft2. Plots were 3 ft x 6 ft and arranged in a randomized complete block design with four replications. Dollar spot occurred naturally and plots were not inoculated. Disease severity was assessed as the number of dollar spot infection centers per plot every two weeks from 1 Jun to 11 Aug. A standardized area under the disease progress curve (SAUDPC) was used to evaluate disease progress over time. SAUDPC was calculated using the following formula: Σ [[(yi+ yi+1)/2] [ti+1 - ti]]/n, where yi and yi+1 represent disease rating at two consecutive dates, ti and ti+1 represent the corresponding rating dates to yi and yi+1, respectively, and n represents the number of days between the first and last rating dates. Data were 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 (3 fl oz/1000 ft2) or Tekken had lower dollar spot severity from 15 Jun – 11 Aug than plots treated with Daconil Ultrex alone or with UMD-DS-B-1 at 2 fl oz/1000 ft2. Plots treated with UMDDS-B-1 (3 fl oz/1000 ft2) or Tekken alone had lower SAUDPC values than other fungicide treatments. Phytotoxicity was not observed following fungicide applications. •

z Letters indicate the date of application: A:18 May, C:1 Jun, D:8 Jun, E:15 Jun, G:29 Jun, I:13 Jul, J:20 Jul.

y Dollar spot was visually rated by counting the number of infection centers per plot.

x Means in a column followed by the same letter are not significantly different according to Fisher’s least significant difference (α = 0.05).

w Standardized area under the disease progress curve is a quantitative measure of dollar spot intensity with time over all rating dates.

Dollar spot: Treated plot (Tekken) on the top and non-treated plot below.