Investigating Mechanisms of Dollar Spot (Rutstroemia floccosum syn. Sclerotinia homoeocarpa) Reduction through Light-Weight Rolling On Creeping Bentgrass (Agrostis palustris) Putting Greens.

Dollar spot, caused by the fungal pathogen Rutstroemia floccosum, is one of the most important diseases to affect golf course turf grasses in the United States. More money is spent to manage dollar spot than any other disease on golf courses (Vargas, 2005). A study to investigate the effects of light-weight rolling on the reduction of dollar spot was conducted at the Hancock Turfgrass Research Center on the campus of Michigan State University in 2008 and 2009. Light-weight rolling has previously been shown to contribute to disease reductions on turfgrass (Nikolai et al., 2005; Inguagiato et al., 2009), however mechanisms involved remain debated. Creeping bentgrass (Agrostis palustris) plots subjected to daily (5 days week^-1) rolling treatments resulted in significantly less disease when compared to a non-rolled control. Morning rolling treatments and afternoon rolling treatments were implemented to investigate the effects of dew and guttation fluid removal and dispersal. Treatments rolled in the p.m. (after dew and guttation naturally dissipated) exhibited similar disease reduction as treatments rolled in the a.m. (while dew and guttation fluid were present) when compared to the control. Cumulative effects of rolling were investigated with treatments rolled twice (2x) day^-1. The 2x rolling treatment exhibited significantly less disease than all other treatments and resulted in significantly higher upper rootzone soil volumetric water content means in both 2008 and 2009, when compared to the control. Microbial populations were evaluated via phospholipid fatty acid (PLFA) analysis in order to investigate potential effects of rolling on microbial abundance and dynamics in the upper rootzone (Vestal and White, 1989; Zelles, 1999). Rolled treatments exhibited significant increases in particular fatty acid abundances associated with common bacteria. Furthermore, a general trend towards increased total bacterial PLFA abundance was present in rolled treatments. These results suggest that daily, season-long, light-weight rolling on turfgrass putting greens may be contributing to disease reduction by altering microbial populations in the upper rootzone. Additionally, data suggest that mechanisms other than dew and guttation dispersal may be responsible for disease reduction due to the observed dollar spot inhibition from afternoon rolling.