Virginia Grape Disease Updates

Thanks for attending today's online Extension meeting. Please find the materials I discussed today below. 1) Presentation slides (will open a new window with a pdf file). 2) List of short PHI materials for Botrytis, powdery mildew, and downy mildew.

Central and northern VA received much-needed rains in the past two days. Looks like the chance of thunderstorm is high in today and tomorrow too. Several people asked me whether they need to jump on their tractor now and spray for downy mildew or not. Here are snapshots of downy mildew risk events in three locations during the past two weeks. Southwestern VA, Floyd: none Central VA, Afton: 7/11, 7/22, and 7/23 Northern VA, Winchester, 7/11 (a very short one) and 7/22 Since we have been experiencing a very dry season, I do not think we need to react to every rain event, especially if your previous spray was less than 7-10 days ago . If you are due to spray soon anyway, it may be a good idea to have a Phos acid material (e.g., Prophyt, Phostrol, Agri-Fos, etc.) in the tank-mix as insurance. For example, my previous spray (a fixed copper material) was on the 11th and my plan is to spray my vines this Saturday (the 25th) with a Phos acid, sulfur, and another PM material (Vivando,

Here are snapshots from the NEWA risk models from the past two weeks. Floyd: no black rot or downy mildew infection events Afton: black rot and downy mildew infection event on 7/1-2. Winchester: downy mildew infection event on 7/8 Looks like we are having relatively dry conditions. Depends on where you are and which cultivar you grow, you may not need to worry too much about downy mildew or black rot for a while. Also, most of our vines are done with the critical period of cluster susceptibility to black rot, downy mildew, and powdery mildew. What I would keep eye on will be powder mildew, since the pathogen does not require water for infection. Sulfur is a good material, and you can add powdery mildew materials, such as Quitec, Vivando, Torino, DMI, and SDHI to provide extra protection. When you spray a sulfur product, make sure the sprayed material will be dried up before temperature gets above mid-90F. If the leaf surface is wet with sulfur when the temperature gets high, it