Virginia Grape Disease Updates

We did not receive any considerable rain during the weekend.  At this point, I am not certain what to believe.  I think the atmosphere is unstable and conducive to create thunderstorms.  We are expecting 30-40% chance of thunderstorm from tomorrow to Sunday. I have seen a small outbreak of mealybugs in our field (please click the picture to see a larger image).  It is a good news for me because I was looking for them, but as you may know, this insect can vector a virus that can cause grape leaf roll disease.  Thus, if you have seen these bugs, please contact me so that I can visit your place to collect samples.  It is very important for us to know which species are present in VA in order to understand the risk of leaf roll spread.  It is a part of on-going leaf roll project and we need more information on this important pest.  Mealybugs are about less than 1/8 of an inch in length and often covered by white hair-like tissues.  Often time, y...

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...

As of noon yesterday (4/28/09), our Chardonnay was 100% bud break with more than 50% of them with lower two leaves unfolded. Some were as advanced as the picture. Cabernet sauvignon varied with vines, but some were close to 70% bud break with a few buds with lower leaves unfolded, and others were about 30%. This morning, we had a shower (~0.08 inch from 6:40 am to 8:45 am, average temperature was around 52F). The rain was short, but RH has been fairly high after the rain, thus it may be enough for Phomopsis to cause light infection; however, considering how dry we have been, it may not have much activity by this fungi to initiate spore production and release. This rain was little shy for condition for powdery mildew fungi to release its spore (ascopsore) to the air (it requires 0.1 inch or more plus 2.5 hr of wetness at >50F) . We are expecting series of short rain events in next few days. I'll keep track of them as much as I can. I'm heading to a vineyard meeting...