Reducing Ultraviolet-B Radiation Affects Dollar Spot Development Under Field Conditions.

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is a destructive disease of creeping bentgrass (Agrostis stolonifera L.). Temperature and humidity are two environmental parameters commonly used by researchers and turfgrass managers to predict dollar spot epidemics. However, little is known about other environmental parameters affecting dollar spot development. A two-year (2013-2014) field experiment was conducted at the East Tennessee Research and Education Center in Knoxville, TN, to determine the effects of ultraviolet-B (UVB) radiation on dollar spot development. Plots of creeping bentgrass (cv. ‘L 93’) were maintained at 4 mm and were screened with frames covered with plastic filters designed to either transmit all solar wavelengths or to mostly exclude the UVB (315-280 nm) spectrum. The UVB transmitting control treatment (UVB+) was covered with a polystyrene sheet (1.3 mm) while the UVB excluded treatment (UVB-) superimposed a Mylar film (250 µm) on the polystyrene sheet. The Mylar film excludes most ultraviolet radiation with wavelengths less than 310 nm. The filters were placed 40 cm above the turfgrass canopy to minimize interference with the ambient environmental conditions. Dollar spot incidence (visual infection center count) and disease severity (%, via digital image analysis) were evaluated two to three times weekly. During both years, the UVB- plots exhibited significantly greater dollar spot incidence and severity on most rating dates compared to the UVB+ plots. Additionally, the UVB- plots resulted in significantly higher dollar spot incidence and severity as measured by the area under the disease incidence progress curve (AUDIPC) and area under the disease severity progress curve (AUDSPC). Results of this study suggest that S. homoeocarpa is sensitive to UVB radiation under field conditions. This sensitivity may lead to novel disease management techniques and improved disease forecasting models that account for the impact that UVB radiation has on this pathogen.