Virginia Grape Disease Updates

I have been receiving more than usual number of calls and emails about powdery mildew this year.  It seems that consensus is that it started to show up on clusters last week and just keep going.  We have passed critical time for cluster infection at this point, thus, you may wonder how it happened?  Since it takes 7-10 days to develop symptoms (powdery appearance on the surface, i.e., spores), and it probably takes a few generations prior to the explosive outbreak, thus, the initial infection events probably took about 20-25 day ago when berries are still susceptible. Management options on on-going powdery mildew infection is limited.  As with other diseases, we do not have real curative or eradication material against powdery mildew.  Also, it is not recommendable to apply protectant fungicides because there will be higher risk of fungicide resistance development; however, as I mentioned in the previous post, there are a few options that can help you out.  All of them requires throu

I have received several emails and phone calls regards to downy mildew and Botrytis last week.  Also, some people are struggling with powdery mildew.  Here are general options against these diseases at this time of the season. Downy mildew :  At this point, your berries are out of susceptible period.  However, because of the last minutes rain some of us had about two weeks ago, some locations are experiencing downy on clusters.  Thing is that the infection took place a while ago, and there are not much options available.   For kick-back activity, you can use Ridomil Gold Copper (note: it also have 42-day PHI), or Phosphorous acid materials such as Prophyt or Agri-Fos (0-day PHI).  However, please keep in your mind that kick-back activity is for on-going infection, but not for already established colonies (i.e., if you see downy growth, these are established colonies).  If there are only minor colonies, you may able to keep them contained in the small area by applying these materials.

I thought I posted it, but apparently I did not!  Winchester area received two showers on 8th (Friday), both events were short, and temperature during the events were about 70F.  The first event was longer (~5 hours, but the amount of precipitation was very small (0.02 inches total).  The second event was short (~3 hours), and it was a thunderstorm.  It was downy mildew infection events, but since previous two days were relatively dry, it might not be a big risk.

I hope everybody is having a nice 4th of July. :) After I posted yesterday, thunderstorm went through Winchester area around 5:50 PM, then there were rains here and there, then the RH was high (>90) until 8:00 AM this morning.  Thus, it was almost 14 hours of estimated wetness event with an average temperature of 70F.  It was Phomopsis, black rot, and downy mildew risk event, and as I noted yesterday, Botrytis can cause infection under this condition as well. It looks like more thunderstorms are coming our way.  We will see... Also, there will be a vineyard meeting at Barren Ridge this Wednesday.  If you can make it, please stop by.  We will cover seasonal viticulture and disease management tips. 984 Barrenridge Road, Fishersville, VA 22939-3026 http://barrenridgevineyards.com Phone (540) 248 3300 Directions : Take I-64 West.  After crossing Afton Gap at crest of Blue Ridge Mtns. Continue on for 8 miles.  Take Exit 91 and turn right onto Va 285/ State Rt. 603.  Trav

Winchester area received rains this morning from around 2:30AM until 4:00AM.  Then the RH was high (>90%) until 8:30AM or so.  Thus, it accounted for 6 hours of estimated wetness with an average temperature of 70F.  It was Phomopsis, black rot, and downy mildew risk event.  We are about to exit from critical period for berry infection by black rot, downy mildew, and powdery mildew.  I just finished my second cover after bloom for my trials yesterday (just in time for the rain :) ).  There are many powdery mildews and a hint of downy in my vineyards.  I hope that you have clean clusters up until this point.  After this critical period, you can relax a bit.  Also, although it typically requires a longer wetness event in the field, Botrytis can cause infection under the same condition as we seen today.  Probably because of humid nights we experienced in the last two weeks, I have already seen development of Botrytis on our Chardonnay clusters.  Plus, I have heard from others that