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Dollar spot of amenity turf, caused by Sclerotinia homoeocarpa, occurs in two seasonal epidemics in the northern United States, one from May to late July and a second from mid-August through October. It is not known whether these seasonal epidemics are the result of multiple species or due to seasonal variation within a single species. Isolates of S. homoeocarpa were collected from dollar spot lesions obtained from golf courses in Michigan, Illinois, and Wisconsin. Vegetative compatibility reactions between isolates identified six vegetative compatibility groups (VCGs) among more than 1,300 isolates collected from the eight locations. Most VCGs were present throughout the season, but one was generally recovered only in the late epidemic. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) were identical among VCGs, indicating that the VCGs represent a single species. The results of this study suggest that the seasonal dollar spot epidemics observed in the northern United States are caused by a single species.

Seedhead production of annual bluegrass (Poa annua L.) during the spring reduces annual bluegrass root production and disrupts the aesthetic and playing qualities of the turf. A method of predicting when annual bluegrass seedheads visually emerge through maximum production would be a benefit to turf managers in that management practices such as vertical mowing and core cultivation could be suitably adjusted. A model to predict the number of seedheads from visual emergence through maximum production for a perennial annual bluegrass turf was developed from three field locations in Michigan. The proposed model is seedhead no. = -6249.4 + 41.099 (DD) -0.08573 DD 1 + 0.0000575 Dl)l where DD = degree-day accumulation above 286 K beginning April (R 1 = 0.65).

Mefluidide [N‐(2,4‐dimethyl‐5‐{[(trifluoromethyl)sulfonyl] amino}phenyl) acetamide] is an effective growth regulator for annual bluegrass [Poa annua var. reptans (Hauskins) Timm.] seedhead suppression. The effectiveness of mefluidide is dependent on the rate and timing of application. The objective of this field study was to determine the lowest effective rate and the proper time for mefluidide application based on growing degree‐days (GDD). Soil types were a fine, mixed, mesic Aeric Ochraqualf and fine‐loamy, mixed, mesic Typic Glossoboric Hapludalfs for Columbus, OH, and East Lansing, MI, respectively. The rates evaluated were 0.140, 0.070, and 0.035 kg ha−1 of mefluidide. The applications were made at 15, 25, 30, and 45 GDD. Degree‐days were accumulated using a sine curve as an approximation of the diurnal temperature curve. The base temperature used was 13°C. Mefluidide applied between 15 and 30 GDD at 0.140 kg ha−1 gave excellent seedhead suppression. Mefluidide applied between 15 and 30 GDD at 0.070 kg ha−1 gave moderate seedhead suppression. Applications of mefluidide at 45 GDD or at the 0.035 kg ha−1 rate were unacceptable.

The antifungal activity of the herbicides bialaphos and glufosinate, the active moiety of bialaphos, was assessed. Bialaphos showed a higher level of in vitro antifungal activity againstRhizoctonia solani, Sclerotinia homoeocarpa, andPythium aphanidermatumthan glufosinate. Glufosinate suppressed the mycelial growth ofR. solaniandS. homoeocarpa, but it had no inhibitory effect onP. aphanidermatumup to the highest concentration in our testing regimes. Various concentrations of bialaphos solutions were applied to transgenic, bialaphos- and glufosinate-resistant creeping bentgrass inoculated with fungal pathogens. Bialaphos applications were able to significantly reduce symptomatic infection byR. solaniandS. homoeocarpaon transgenic plants. Bialaphos significantly inhibitedP. aphanidermatum, but not to the same degree thatR. solaniandS. homoeocarpawere inhibited. These results indicate that bialaphos may provide a means for the simultaneous control of weeds and fungal pathogens in turf areas with transgenic, bialaphos-resistant creeping bentgrass.

Antifungal extracts from four strains of bacteria that were selected for their ability to inhibit fungal turfgrass pathogens were compared for in vitro activity. The cell extract from Pseudomonas aureofaciens Tx-1 (ATCC 55670) exhibited the greatest antifungal activity against selected turfgrass pathogens. Purification of the extract yielded a single active component that was identified as phenazine-1 carboxylic acid (PCA). Minimum inhibitory concentrations of PCA to tested fungal pathogens ranged from 10 to 25 µg/ml. In greenhouse studies, PCA provided management of dollar spot on creeping bentgrass equal to that of the commercial fungicides triadimefon and chlorothalonil at equivalent rates of active ingredient. Phytotoxic effects were observed on creeping bentgrass in greenhouse but not field evaluations of PCA at the rate of 0.48 g/m2. At the end of 2 years of field study, PCA applied every 14 days at 0.15 g/m2 provided dollar spot management on creeping bentgrass equal to that of chlorothalonil applied every 10 days at the label rate of 0.48 g/m2.

Dollar spot (DS) (Sclerotinia homoeocarpa F.T. Bennett) is an important disease on golf course turfgrasses in the United States. The objective of this study was to elucidate disease reduction mechanisms related to lightweight rolling. Creeping bentgrass (Agrostis stolonifera L.) plots that were subjected to daily (5 d wk−1) rolling treatments (1x a.m., 1x p.m., 2x a.m.) showed significant DS reductions when compared with a nonrolled control. Treatments rolled in the afternoon (after dew and guttation fluid dissipated) exhibited similar area under disease progress curve (AUDPC) values as treatments rolled in the morning in 2008, 2009, and 2010. Both 1x rolling treatments resulted in significant DS reductions compared with the control in 2009 and 2010. The 2x d−1 treatment exhibited significantly less DS than the control in all years as well as significantly lower AUDPC values than both 1x rolling treatments in 2009 and 2010. Rolling 2x d−1 improved turfgrass quality compared with all other treatments in each year of the study. All rolling treatments exhibited higher root zone volumetric water content (%VWC) compared with the control in 2010, and significant effects on %VWC were observed on individual dates among treatments. Results indicate previously unidentified effects of rolling on putting greens, including added physical and biological effects, which may be contributing to DS suppression.