Virginia Grape Disease Updates

Some of our early cultivars such as Alandale is changing it color.  It is just a matter of time to see other cultivar to enter phase of veraison.  Hopefully, we will keep seeing dry weather with little bit of rain here and there.... There are several diseases to be considered at this stage.  One of them is Botrytis.  The spray timing for Botrytis is at bloom, bunch closure, and veraison.  The pathogen seems to be active throughout the season, but Botrytis likes berries when they get mature and accumulate more sugar.   As usual, canopy management is the first line of defense against grape disease management and this is particularly true for Botrytis since it tends to develop after a long period (15-17 hours) of high humidity condition. Please keep in your mind that Botrytis is very well known for its capability to overcome fungicides.  Thus, a rotation of mode of action groups is very important aspect for Botrytis management.  The ...

I have received several emails about black rot recently.  With the frequency of rains we observed so far, it is not surprising to see small amount of black rot even if you had a very good coverage of fungicide. Typically black rot starts off as brown discoloration on the berry, and associated with production of fruiting bodies which are often look like black dots (the size of ground black pepper?).  The picture above is not the best, but you see black dots on the one at the top of the picture.  Eventually, the infected berry will become hard and dry mummified berry with a lots of fruiting bodies, which you can see here and there in the picture. If you are seeing something like the picture above, chances are the infection happened at least two weeks ago when berries were susceptible to the infection by black rot pathogen (and so as by powdery mildew or downy mildew pathogen).  I can say that because it takes about 2 weeks after infection for black rot pathoge...

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 Botr...

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 p...

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.