From Brooke Warres, graduate student in Plant Pathology at the University of Georgia.
Powdery mildew, caused by the fungus Erysiphe necator, has been found at the UGA Mountain Research Station in Blairsville, GA. The disease was observed on an untreated vine in a fungicide trial. Make sure that your current spray program includes active fungicides that protect against powdery mildew; resistance to QoIs has been frequently observed, so please be cautious. This fungus infects both leaves and fruit of grapes. If the fruit is infected early, the berries may crack as seen in one of the pictures below. Make sure you are scouting regularly for this and other diseases! Contact your local county agent if you have questions about this disease or any other aspects of grape production.
Phil Brannen is a Professor in the Plant Pathology Department at the University of Georgia. He attended the University of Georgia for his undergraduate degree in Plant Protection and Pest Management, where he also received an M.S. in Plant Pathology, followed by a Ph.D. in Plant Pathology from Auburn University. He has extensive experience with disease management programs in numerous cropping systems. He serves as the extension fruit pathologist for Georgia – conducting research and technology transfer for multiple fruit commodities. His efforts are directed towards developing IPM practices to solve disease issues and technology transfer of disease-management methods to commercial fruit producers. He also teaches the graduate level Field Pathology Course, the History of Plant Diseases and their Impact on Human Societies Course, team-teaches the IPM Course, coordinates the Viticulture and Enology in the Mediterranean Region Course (Cortona, Italy), and guest lectures in numerous other courses throughout the year.