Influence of Mowing Frequency and Plant Growth Regulators On Dollar Spot Severity.

Management of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) on golf course fairways is becoming increasingly challenging.  The objectives of this study were to 1) determine the influence of mowing frequency on dollar spot; and 2) evaluate the influence of plant growth regulators (PGRs) on disease severity.  Two season-long studies were conducted on a ÔPutterÕ creeping bentgrass (Agrostis stolonifera L.) fairway at the University of Connecticut.  Turf was mown 2, 4, or 6 d wk^-1 to a height of 1.3 cm.  Mowing was performed in the afternoon hours to eliminate the confounding effect of mowing frequency on leaf wetness displacement.  PGR treatments included paclobutrazol and trinexapac-ethyl applied on a 21-d interval, and a non-treated control.  The study was conducted between 1 June and 28 September 2007 and 30 May and 1 October 2008.  In both years, dollar spot severity was reduced by 63% to 90% in plots treated with paclobutrazol, when compared to the non-treated control.  Disease severity was reduced by 13% to 52% in plots treated with trinexapac-ethyl on select dates in 2007 and 2008.  On several dates in both years, dollar spot severity was 23% to 50% lower in plots mown 2 days week^-1, when compared to those mown 6 d wk^-1.  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 trinexapac-ethyl that were mown 2 d wk^-1, when compared to those mown 6 d wk^-1.  Reductions in plots mown less frequently were less consistent in those receiving paclobutrazol or no PGR.  Results indicate that use of plant growth regulators combined with less frequent mowing may reduce dollar spot severity in the absence of fungicides.