The warm May pushed our vines forward rather quickly. Many people in northern VA are about to see blooms (our 3-year old young Chardonnay vines are trace bloom), and I am sure rest of regions are going through bloom by now. This means that many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot. Bloom time is also critical period to prevent Botrytis, ripe rot and Bitter rot, because pathogens of these diseases can infect flower parts and come back later. We do have materials with kick-back activities against downy (Ridomil products, Phosphonates, etc.) and black rot (myclobutanil, etc.), but infection on flowers and young fruits can happen very fast. Unless we have a very dry season, this is the time where you have to be proactive. (Note: recent warm and humid night time conditions are favoring spore production of downy mildew pathogen) Thus, what I recommend often is use of protectant materials to p...
Grape Disease Management Tips from Mizuho Nita (Grape Pathologist at Virginia Tech)