Are you seeing powdery mildew in your vineyard this season? If so, we would love to sample it, as it could mean that your fungicide program is breaking down due to resistance development in the powdery mildew fungus. One of our graduate students in the University of Georgia Plant Pathology Department, Brooke Warres, is working on QoI and DMI fungicide resistance in powdery mildew. She can take swab samples of the mildew from any part of the grapevine to test for mutations associated with resistance to these chemical classes. With this information, we can better understand resistance patterns in Georgia and determine how widespread these mutations are in our state.
As you are scouting your vineyard at the end of the season, we suggest looking inside the canopy to check for white to gray fungal growth of powdery mildew — predominantly on the upper leaf surfaces. Depending on how well it has been controlled, it may also be self evident on the canopy exterior. If you are finding this disease, please call Brooke at 678-642-2183 or email at Brooke.Warres@uga.edu so she can visit to take a quick sample. With these samples, she will be able to let you know if you currently have QoI and/or DMI resistant populations in your vineyard. This should help you to plan your spray program for next season.