Virginia Grape Disease Updates

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,...

Here's my handout from last week's meeting at Stone Tower Winery . Thanks for those who attended the meeting! It looks like we may have rains here and there this week. Since we have not had significant rains in the past week or so, the risks of downy maybe low, but most of us are still in the middle of critical period for cluster protection. Please refer to my at bloom post for more details on disease management tips for this time of the year . Once we pass this period, we can relax a bit, in terms of fungal disease management.

At Winchester area, we ended up having a pretty good weekend. There were several periods with rain, but it was not as extensive as the forecast. We received about an inch total over 2-3 days. However, it looks like the central VA received more rain than we did. I would like to share a question I received from a grower today. "With all of the rain events we have had lately and bloom being an important stage for fungicide application Should we spray after a significant rain event before the recommended 7-14 day interval? Specifically, I applied fungicide June 3rd and received quick but heavy rainfall on the 4th and 5th. Riding through the vines it looks as though there is still chemical residue on leaves and clusters. Can I base a decision off of this observation?" It really depends on what you have sprayed, what we are expecting in the next few days, how the vines are maintained (shoot thinning, etc), cultivars, etc, so, I cannot give you a quick answer. Typically...

Our Chardonnay vines are getting close to full bloom, and of course, we are expecting more rain over the weekend. Just an another reminder that from bloom to 4-5 weeks after bloom is the critical period for downy mildew, black rot, and powdery mildew infection on clusters, and at bloom application is very important one for Botrytis management.  Please see recent post about the at bloom fungicide application consideration as well as recent updates on fungicides. This would be the timing where you will thrown in some good materials into your tank mix! It is much easier to protect the vines than try to play a catch up game after disease outbreak,