Interactions Among Mowing Frequency and Plant Growth Regulators On Season-Long Dollar Spot Control with Fungicides.

Mowing and use of plant growth regulators (PGRs) are basic cultural practices performed on golf course turf.  However, the influence of mowing frequency and PGRs on the residual efficacy of fungicides used to control of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is unclear.  The objective of this study was to elucidate interactions among mowing frequency, PGRs, and fungicides on seasonal management of dollar spot.  Two season-long studies were conducted on a 1.3 cm height ÔPutterÕ creeping bentgrass (Agrostis stolonifera L.) fairway at the University of Connecticut. The interactions among mowing frequency (2, 4, or 6 d wk^-1), PGRs (paclobutrazol or trinexapac-ethyl), and fungicides (boscalid, chlorothalonil, iprodione, or propiconazole) on dollar spot control were assessed.  Treatments were initiated in the late spring of 2007 and 2008, and each individual fungicide treatment was subsequently re-applied only when dollar spot reached a threshold of 5 infection centers plot^-1.  Survival analysis of days until threshold met revealed that lengths of control (LOC) of fungicides in plots receiving paclobutrazol were 24% to 83% longer, when compared to plots not receiving a PGR.  LOC by fungicides was generally similar between plots treated with trinexapac-ethyl and no PGR.  In 2007, LOC values for iprodione were 23% longer in plots mown 2 d wk^-1, when compared to plots mown 6 d wk^-1.  In general, however, mowing frequency did not influence LOC.  The early curative application timing employed in this study generally provided acceptable disease suppression for boscalid and propiconazole, but not for chlorothalonil or iprodione.  Results from this study indicate that paclobutrazol may lengthen the treatment interval of fungicides and increased mowing frequency is likely to have little impact on fungicide residual efficacy.