P-297 - Combination wavelength UV-C application for the multi-targeted suppression of grape powdery mildew

Abstract Text: The use of ultraviolet germicidal light (UV-C) has proven to be an effective powdery mildew management strategy for a variety of crops including grapevine. Addition of twice weekly nighttime application of 254 nm UV-C at 200 J/m² to a fungicide regimen was found to significantly reduce grape powdery mildew (GPM) disease in small research plot trials in the Willamette Valley, OR. However, the energy required to impact Erysiphe necator development and the required dark periods before and after UV-C irradiation limits commercial UV-C application. To address these concerns, we evaluated the combination of different wavelengths to target multiple cellular processes in E. necator conidia in a lab setting. UV-C light wavelengths of 254 nm and 265 nm directly target nucleotides while 222 nm damages DNA repair proteins. E. necator spores were settled onto gelzan media-filled 24-well plates and irradiated immediately after spore deposition with the three different UV-C wavelengths listed above using a conveyer belt to simulate field exposure. Effective dose was regulated by adjusting belt speed and sample distance to light source. Triple wavelength combination treatment significantly reduced E. necator spore germination compared to individual wavelengths and all paired wavelength combinations. These results appear to indicate that targeting multiple cellular processes by UV-C wavelength has potential for management of GPM.