Photo: we have started to see powdery mildew on clusters. I hope you are not!
Looks like series of thunderstorms are hitting various part of the state this week. Just a reminder that due to April frost events, some of us experienced extended bloom. This not only means potential lag in harvest time for these late clusters, but also, an extended critical period for seasonal diseases. Grape clusters are susceptible to black rot, downy mildew, and powdery mildew from bloom to 4-5 weeks after bloom (3-4 weeks for American grapes). Thus, this is the time I want you to be on top of the game (i.e., nice coverage, 7-10 days interval, good selection of fungicides to be applied).
Many growers told me that if they are clean around the Fourth of July weekend, you don't expect outbreak of black rot, downy mildew, and powdery mildew. I generally agree with their assessments since in many years, bloom happens late May or early June. However, this year, bloom started the first week of June, but I saw delayed bloom until the middle of June, thus, I will keep my schedule relatively tight until early to mid-July (i.e., rather than the Fourth of July weekend, I would aim for the next weekend). Since we are having several rain events in the past few days, I would watch the forecast carefully, and prepare for good protection against, downy (e.g., Revus (Top), Zampro, Ranman, mancozeb, Phosphite, etc), black rot (DMI (Rally, Revus Top, Luna Experience, etc), mancozeb, QoI (Pristine, Abound, etc)), and powdery mildew (Vivando, Luna Experience, Quintec, Tanos, sulfur, etc). Please note that some of mixed materials may have efficacy on multiple diseases.
Also, we will have a vineyard meeting at Arterra Wines in Delaplane, VA from 11:00 AM tomorrow. I hope to see you there!