debor039

Looks like we have openings in the sky today and tomorrow.  What a wet year! Here's a copy of handout from the extension meeting held at Loudoun county last week .  It covers weather condition at Winchester, seasonal updates, and fungicide updates.

Since we are expecting heavy rain event on Saturday, plus about to be done with the critical time for cluster infection by downy mildew, powdery mildew, and black rot (which last 4-5 weeks after bloom), I received a several emails about the application timing.  As with other timings, it really depends on so many factors, but here's my take on it.      If you have a history of black rot and downy mildew in your vineyard, you may have a higher disease risks.  If you are in this situation, AND if you think that your previous application was waring off, then you may need to apply some protection before the rain.  However, if your previous application was within 7-day or have not seen many rains, or not having much issue with downy or black rot, then you probably do not need to panic.     A good news is that it looks like we have an opening after the Saturday's rain event.  (then a few more days of rain in the early part of the week)...

Most of us are about to see the end of critical time for berry infection by black rot, powdery mildew, and downy mildew.  Please keep up as much as you can with protection of vines for next few weeks.  I know many of us experienced some degree of flower and berry infection by either black rot or downy mildew due to frequent rain events, but once we pass the critical period (4-5 weeks after bloom for most of cultivars, and maybe 5-6 weeks for some susceptible varieties), these pathogen cannot cause disease on mature berries. The next critical spray is for Botrytis at bunch closure and veraison.  Make sure to remember about rotation of mode of actio n groups as well as tank mixing.  Since many of Botrytis specific materials are prone to have fungicide resistance issue, it is better to mix with a broad spectrum material such as captan or copper.  (Mancozeb can be used too, but we are approaching to the 66-day PHI.)  Another important IPM component for Botrytis...

The warm May pushed our vines forward rather quickly.  Many people in northern VA are about to see blooms (our 3-year old young Chardonnay vines are trace bloom), and I am sure rest of regions are going through bloom by now.  This means that many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot.  Bloom time is also critical period to prevent Botrytis, ripe rot and Bitter rot, because pathogens of these diseases can infect flower parts and come back later. We do have materials with kick-back activities against downy (Ridomil products, Phosphonates, etc.) and black rot (myclobutanil, etc.), but infection on flowers and young fruits can happen very fast.  Unless we have a very dry season, this is the time where you have to be proactive.  (Note: recent warm and humid night time conditions are favoring spore production of downy mildew pathogen)  Thus, what I recommend often is use of protectant materials to pro...

I posted general "rule of thumb" about application (or re-application) earlier this season .  Dr. Annemiek Schilder at Michigan State University recently published a very nice write up about it. She answers many of questions we have in our mind, when the fungicide residues to be washed off from the rain, efficacy of spreader-stickers, and systemic fungicides.  Please check it out.

Today is the one of the days when you find many things in the vineyard!  Mealybugs (white one in the middle of the picture) are also observed, mainly at the base of the shoot (or a spur in this case).  You also see a scale insect on this picture.  Please note that both mealybugs and scale insects can transmit several virus pathogens, including the ones cause grapevine leafroll disease .   Unfortunately, once the vine is infected, only remedy is removal of the infected vine.  (However, please note that the presence of leaf roll virus does not always results in immediate loss of crop.)  If you have both mealybugs and virus infected vines, and have a plan of expansion, it is probably a good idea to protect new vines using insecticides.  However, you have to make sure you have both the virus and mealybugs to justify your action since insecticides for mealybugs are relatively expensive, and as with other chemicals, application of unnecessary insecticide is ...

On the previous post, I mentioned that "At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom." However, it looks like at out site, the downy mildew pathogen is taking advantage of the weather conditions.  Although our last application of mancozeb and sulfur was only 6 days ago, I noticed that some of older leaves show symptoms of downy mildew (i.e., the infection might have happened prior to the previous application).  At this point, many of leaves look like the first picture, and disease incidence is probably less than 0.5%, thus, it is difficult to find them; however, we came across with a few leaves with clear symptoms as in the...