Virginia Grape Disease Updates

I've been in and out of my office with my leaf roll survey project, and it has been bit difficult to frequently update the blog. Also, at this point, not much you can do about major fungal diseases. The critical time of infection is gone. If you see downy, powdery, or black rot on your bunches, the infection probably took weeks ago, if it was not a month. Thus, I will point some key issues at this time of the year. Botrytis, downy, and other rot We had a long period of wet and cool nights during the last half of August. This conditions favors both Botrytis and Downy mildew sporulation, and potential infection on nearby leaves. (i.e., it won't spready quicky, but it probably enough to increase number of spores.) If it is followed by rain (like we had last week), the risks of Botrytis and downy mildew increase. As I mentioned earlier, downy mildew won't touch berries at this point. Berries are resistant to the infection. However, with a prolonged rain or high hu

We had fairly dry month so far and grasses are start to getting brown, but a thunderstorm dropped about 0.5 inch of rain last Friday around Winchester area. It stared little after 5:30 pm then continued for two hours or so. The relative humidity was high until next morning (10:30 am) with an average temperature of around 70F. This accounted for infection event for Phomopsis and Botrytis on berries and Downy mildew on leaf. I listed Phomopsis here simply because it can infect berries at any time; however, often time infection around this time is not common. It is probably due to less inoculum (this fungus mainly creates the fruiting body in the spring), and it favors cooler climate. Thus, your risk depends on how chronically you have Phomopsis in your vineyards. If Phomopsis appears year after year, then your risk is higher. If you just see them only when we have a wet spring as we did this year, you probably have less risk. As for downy mildew, I started to see foliar sympt

(A graft union infected by fungal organism(s)) We had a very nice workshop this Monday. Now everybody become experts of various trunk diseases! As Philippe discussed, most of fungal pathogens that cause trunk diseases often requires a point of entry. In addition to pruning wounds, accidents with a weed-whacker, etc that were in the discussion, due to cold temperature during winter, some of varieties are more susceptible to have cold injury which also can serve as a point of entry for microorganisms. Site and variety selection can play a big role in prevention of these diseases. As for other diseases we face, we had several nights with high relative humidity (8/14-16) which favors downy mildew sporulation. Then we had thunderstorm passed by on 17th and 18th. Thus, if you had visible downy mildew colonies on your leaves, the risk of new infection was high during these thunderstorms. (I'm talking about leaf infection, not berries.) At Winchester, last night's thunderstor

We will have Virginia Vineyards Association's summer technical meeting at Jefferson vineyards on August 17th (this Monday). Dr. Philippe Rolshausen and Lucie Morton will be talking about trunk diseases. I will be there to provide some help and learn more about trunk diseases. If you would like to talk to me about other diseases or discuss about your spray programs, please let me know.

Hi all, I'm back from the meeting. It was a meeting for plant pathologists, and it was a very good meeting for me to meet new people (since I'm a new kid on the block and all), as well as my other colleagues. I visited Washington's Yakima Valley grape growing area after the meeting to visit a collaborator on grape leaf roll disease project. There are very exciting area to study, and I will talk about it more in detail within a few days. The picture was taken from their field and showing mealybug infestation. In anyway, I took a quick look at what happened (weather-wise) during my trip. It seems like there are very short rains on 7/31, 8/1, and 8/5, and these were not so significant in terms of major fungal disease infection. We had 4.5 hour of wetness on 8/2 which probably accounted for downy mildew infection (primary on leaves, at this point), and 9.5 hours of wetness on 8/6, which probably accounted for downy mildew and Botrytis (and maybe black rot, if your berr

I'm at a conference until 8/11. In the mean time, we will have a vineyard meeting at Winchester AREC on 8/5. I cannot attend, of course, but I prepared a note (click here to view) and Tony will go over it. Since I may not able to update this blog, I summarized the disease risk at this point. I hope it will be helpful. Disease risks at this point (early August) The critical period for black rot, powdery mildew, and downy mildew fruit infection should be over (4-5 weeks after bloom). Black Rot: Berries should not susceptible any longer. For the next year, make sure to remove all berries from your trellis at or after harvest. These infected berries can produce spores all season long if they are left on the trellis Phomopsis: Berries are susceptible all the time. Since we had such a long period of rain in the spring, you may see some berry infections. Usually, the damage done by Phomopsis is not significant, but if you have reasons to be afraid of Phomopsis, captan can be applie