debor039

At Winchester, the night time relative humidity has been still very high, close to 100%, in nearly every nights in the past three weeks. In addition, we have been observing rapid development of thunderstorms, pretty much every day in the past few days. I know I sound like a broken record, but these conditions favor downy mildew development because downy mildew pathogen prefers to produce spores under dark, humid conditions. Then spores will be spread via rain. At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will initially see infection on the top of the canopy because younger leaves are more susceptible than older ones. Losing the top leaves and laterals are not a big deal; however, once the infection gets severe, it can defoliate many leaves rather quickly (as in the picture above), and that can affect maturing process. Knowing how wet this year has been, it is probably wise to be proactive on dow...

In the last several days, the nighttime relative humidity has been very high (>90%) and temperature has been in the upper 60s ~ lower 70s. This condition is favoring spore production of downy mildew. Please check my previous post about downy mildew management.

Just a reminder on downy mildew management: although the month of July was dry until this week, many of us had a very wet early summer that fostered downy mildew development. In addition, during the last several days, the night time temperature was in low 70s and RH was 95-99%, which was an ideal condition for downy mildew spore production. Thus, if you have not, make sure to protect your vines against downy mildew when you have a chance. If you think you have missed the window, we still have some options. We have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P7, Prophyt, Phostrol, etc.). One of two Ridomil product (Gold MZ) has a mancozeb, which has a 66-day PHI, so, unless you have a late season red, you probably need to use the other formulation, which is Ridomil + copper. Both Ridomil and phosphite are good with kick-back, but you probably want to add a protective material to cover both directions. Examples would be captan (FRAC =...

Thanks again for coming to today's vineyard meeting. I learned quite a bit! Here are my handouts (sorry for not bringing enough today!!) 1) Sprayer calibration handout  (will open a PDF file) 2) Sprayer calibration aid (spreadsheet) (In order to use it, please download onto your computer [File -> Download as...]) 3) Seasonal grape disease reminder  (will open a PDF file)

Most of us are about to finish the critical time when clusters are susceptible to infection by downy mildew, powdery mildew, and black rot.   This critical time varies by varieties, but in general, 4 to 6 weeks and 3-4 weeks from bloom for V. vinifera and V. labrusca species, respectively.   After this critical period, you should be able to relax a bit because these pathogens no longer able to cause disease on berries. So, what’s next?   As usual, disease dynamics really depends on environmental conditions, cultivars grown, and cultural practice, but in general, this is the moment when you will be thinking about late-season diseases such as Botrytis, ripe rot, bitter rot, and sour rot.   The spray timings for Botrytis is at bloom, bunch closure, and veraison.   The pathogen seems to be active throughout the season. The main reason we recommend the application of a Botrytis specific material at bunch closure is that this most likely to be the last opportunity f...

Here are my presentation materials from recent meetings. It will open a new window with a PDF file. 1) Slides from beginner's workshop on 6 June 2018. 2) Handout from the VVA summer technical meeting on 12 June 2018

There will be a meeting in the 23rd of June (Sat) at Rivah Vineyards at The Grove, Kinsale, Virginia. The meeting starts at 6:30 PM. If you are in the Northern neck or surrounding area, please join us.