Mowing Frequency and Plant Growth Regulator Effects on Dollar Spot Severity and on Duration of Dollar Spot Control by Fungicides

Abstract

Putman, A. I., and Kaminski, J. E. 2011. Mowing frequency and plant growth regulator effects on dollar spot severity and on duration of dollar spot control hy fungicides. Plant Dis. 95:1433-1442.Management of dollar spot (incited by Sclerotinia homoeocarpa) on golf course fairways is increasingly challenging. The objectives of this study were to determine the influence of mowing frequency and plant growth regulators (PGRs) on dollar spot severity and on the residual efficacy of fungicides for control of dollar spot. TWo 4-month-long studies were conducted on "Putter" creeping hentgrass (Agrostis stolonifera) maintained as a fairway at the University of Connecticut. Treatments were arranged in a three-hy-three-hy-five factorial that assessed the influence of mowing frequency (2, 4, or 6 days week') and PGRs (paclobutrazol, trinexapac-ethyl, or none) on dollar spot control by five fungicide treatments (boscalid, chlorothalonil, iprodione, propiconazole, or none). Turf was mowed in the afternoon hours to minimize the confounding effect of mowing frequency on leaf wetness duration. Treatments were initiated in the late spring of 2007 and 2008, and each fungicide treatment was reapplied only when dollar spot exceeded a threshold of five infection centers plot'. In the absence of fungicides, dollar spot severity was reduced by 63 to 90% in plots treated with paclobutrazol and by 13 to 55% in plots treated with trinexapac-ethyl. Dollar spot severity was 23 to 50% lower in plots mown 2 days week' compared with those mown 6 days week'. In cases where a significant interaction was observed between mowing frequency and PGRs, dollar spot was reduced on most rating dates in plots treated with trinexapacethyl that were mown 2 days week"' compared with those mown 6 days week"'. Survival analysis of days until threshold was met revealed that duration of control of fungicides in plots receiving paclobutrazol were 28 to 84% longer compared with plots not receiving PGR. Duration of control by fungicides was generally similar between plots treated with trinexapac-ethyl and no PGR. In general, mowing frequency did not influence duration of control. Results from this study indicate that paclobutrazol could be used to increase the treatment interval of fungicides and that mowing frequency in the absence of dew is likely to have little influence on fungicide residual efficacy. When used without fungicides, PGRs and less frequent mowing may reduce dollar spot in situations where fungicide use is limited.

Regulation with Trinexapac-ethyl and Dew Removal at the Time of Fungicide Application Did Not Influence Dollar Spot Control

“…Mowing practices and dew removal strategies associated with fungicide performance for dollar spot control in creeping bentgrass (Agrostis stolonifera L.) have been evaluated recently. Putman and Kaminski (2011) found that mowing frequency (e.g., 2, 4, or 6 d/ week) had no influence on fungicide performance. In another study, Delvalle et al (2011) reported that dollar spot control with fungicides can be extended by daily dew removal or increased mowing frequency.…”

“…Burpee et al (1996) found that when TE was applied alone, it had no significant effect on dollar spot, but when applied in combination with chlorothalonil, iprodione, and propiconazole, it enhanced fungicide efficacy in 1 year of the 2-year study. Putman and Kaminski (2011) reported TE had no influence on dollar spot when applied in combination with fungicides. In the absence of fungicides, however, TE has been shown to significantly suppress dollar spot (Golembiewski and Danneberger, 1998;Putman and Kaminski, 2011).…”

“…Putman and Kaminski (2011) reported TE had no influence on dollar spot when applied in combination with fungicides. In the absence of fungicides, however, TE has been shown to significantly suppress dollar spot (Golembiewski and Danneberger, 1998;Putman and Kaminski, 2011). In another study conducted by Stewart et al (2007), TE rarely influenced dollar spot severity or fungicide performance when applied before the onset of dollar spot symptoms.…”

“…Two of these PGRs, flurprimidol and paclobutrazol, have been shown to inhibit growth of S. homoeocarpa to a greater extent than TE (Burpee et al, 1996). Field studies have shown that when used in combination with fungicides, flurprimidol and paclobrutrazol enhance dollar spot control (Fidanza et al, 2006;Putman and Kaminski, 2011;Stewart et al, 2007).…”

Dollar Spot Control in a Creeping Bentgrass Golf Green with Two Commercial Products Based on Microbial Fermentation and Micronutrients

“…However, Lee et al (2003) reported that none of 12 tested biostimulants (some of them containing microbe extracts) reduced dollar spot in creeping bentgrass when compared with nitrogen applications. Despite the above‐mentioned cultural and biological dollar spot control strategies, the use of fungicides is generally required to maintain acceptable turf quality on golf courses (Putman and Kaminski, 2011), and fungicides have been the most successful tool for managing dollar spot (Walsh et al, 1999). In the United States, greenkeepers frequently apply two or more fungicide products with different modes of action repeated over a 14‐ to 28‐d interval for dollar spot control (Fidanza et al, 2006).…”