Efficacy of Fungicides for Control of Dollar Spot
Efficacy of fungicides for control of dollar spot in a mixed creeping bentgrass/Poa annua soil-based green, 2005.
The test was conducted on a Maury silt loam located at the University of Kentucky Turf Research Center near Lexington. The turf was maintained at 0.188-in. mowing height and fertilized with 1.0 lb N/1000 sq ft as urea on Oct 04, and with 1.5 lb N/1000 sq ft as urea on Nov 04. Plots measured 4 ft x 8 ft with 2-ft borders, and were arranged in a randomized complete block design with three replications. Fungicide sprays were applied using a CO-pressurized hand-held sprayer fitted with Spraying Systems 8003E flat-fan nozzles delivering 1.5 gal/1000 sq ft. Most treatments were first applied on 9 Jun, with the remaining treatments applied according to the schedules indicated in the table (final application on 5 Aug). Where tank-mixes were alternated, sprays were applied every two weeks, with each tank-mix being applied once every four weeks. At each application, treatments were amended with Plant Marvel 20-20-20 at 0.565 lb/1000 sq ft to bring their nitrogen level even with the Gary’s Green Ultrex treatment. Visual counting of dollar spot infection centers were obtained weekly. The level of infestation by Poa annua was visually estimated on 24 May, when color differences between the two grass species and the presence of Poa annua seed heads facilitated discrimination. The amount of Poa annua per plot averaged 40.2% and did not differ significantly between treatments. Transformed data (log) were analyzed using ANOVA and Waller-Duncan k-ratio t-test, (k=100, P≤0.05). Although statistics provided are based on analysis of transformed data, arithmetic means are presented in order to provide a better indication of the level of disease control provided by each treatment as well as the overall disease pressure in the trial.
Disease pressure was moderate to low in this test. There were 33 days with 90 degree temperature from Jun through Aug, with below normal precipitation. Irrigation was maintained at 6 min per station twice a day. The spray programs using phosphite fungicides provided a significant reduction in dollar spot on most assessment dates. No statistically significant differences in dollar spot control was observed among different phosphite fungicides in a spray program. Surprisingly, Bayleton applications did not provide complete control for a 4-wk interval. No phytotoxicity or growth regulator effects were noted in the trial.
z Means within the same column followed by the same letter are not significantly different, Waller-Duncan k-ratio t-test (k=100, P≤0.05). Arithmetic means are presented with statistical groupings based on log10 transformed data.
y One of the two tank-mixes was applied alternately at two week intervals between 9 Jun and 5 Aug.
x Liquid fertilizer formulation; Gary’s Green® 13-2-3+Fe.
w Liquid fertilizer formulation; P-K Plus® 3-21-18 + micronutrients.
v INT= Spray interval (in weeks).
u DAT= number of days after treatment the data were taken.
z Means within the same column followed by the same letter are not significantly different, Waller-Duncan k-ratio t-test (k=100, P≤0.05). Arithmetic means are presented with statistical groupings based on log10 transformed data.
y One of the two tank-mixes was applied alternately at two week intervals between 9 Jun and 5 Aug.
x Liquid fertilizer formulation; Gary’s Green® 13-2-3+Fe.
w Liquid fertilizer formulation; P-K Plus® 3-21-18 + micronutrients.
v INT= Spray interval (in weeks).
u DAT= number of days after treatment the data were taken.