Virginia Grape Disease Updates

Just a quick reminder about the 66-day PHI for mancozeb products. If you are thinking about harvest at the end of August or early September, we are getting very close to the limit. You can switch to captan or copper, but these two cannot control black rot, thus, you may need to add a DMI or QoI fungicide for black rot. At least in our area, it has been dry (relatively speaking) so, depends on where you are, you may or may not need to be concerned about black rot. I see black rot on leaves sporadically in my vineyards, but not in the level I need to be greatly concerned.

It was very nice to see you all at the meeting. Here's the content of my handout. Seasonal grape disease updates For VVA Summer Technical Meeting at Stone Tower Winery 12 June 2019 Mizuho Nita nita24@vt.edu Grapepathology.blogspot.com The critical period for cluster infection: Grape clusters are sensitive to infection by powdery mildew, downy mildew, and black rot from the time of bloom to 4-6 weeks after bloom. The length of this critical time depends on the cultivar, 3-4 weeks for American grapes (V. labrusca),  5-6 weeks for French grapes (V. vinifera), and somewhere between the two for hybrids. Please make sure that you have good coverage during the critical period. In a typical year, once we pass the Fourth of July weekend with a clean canopy, we can relax a bit. We are a week or two ahead of “normal” year, so, you may able to relax sooner this year. Downy mildew: Rainfall is not as intensive as the last year (knock on the woods!), but there are enough to driv