Virginia Grape Disease Updates

Looks like we have openings in the sky today and tomorrow.  What a wet year! Here's a copy of handout from the extension meeting held at Loudoun county last week .  It covers weather condition at Winchester, seasonal updates, and fungicide updates.

Since we are expecting heavy rain event on Saturday, plus about to be done with the critical time for cluster infection by downy mildew, powdery mildew, and black rot (which last 4-5 weeks after bloom), I received a several emails about the application timing.  As with other timings, it really depends on so many factors, but here's my take on it.      If you have a history of black rot and downy mildew in your vineyard, you may have a higher disease risks.  If you are in this situation, AND if you think that your previous application was waring off, then you may need to apply some protection before the rain.  However, if your previous application was within 7-day or have not seen many rains, or not having much issue with downy or black rot, then you probably do not need to panic.     A good news is that it looks like we have an opening after the Saturday's rain event.  (then a few more days of rain in the early part of the week)...

Most of us are about to see the end of critical time for berry infection by black rot, powdery mildew, and downy mildew.  Please keep up as much as you can with protection of vines for next few weeks.  I know many of us experienced some degree of flower and berry infection by either black rot or downy mildew due to frequent rain events, but once we pass the critical period (4-5 weeks after bloom for most of cultivars, and maybe 5-6 weeks for some susceptible varieties), these pathogen cannot cause disease on mature berries. The next critical spray is for Botrytis at bunch closure and veraison.  Make sure to remember about rotation of mode of actio n groups as well as tank mixing.  Since many of Botrytis specific materials are prone to have fungicide resistance issue, it is better to mix with a broad spectrum material such as captan or copper.  (Mancozeb can be used too, but we are approaching to the 66-day PHI.)  Another important IPM component for Botr...