Virginia Grape Disease Updates

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 (...

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...