Virginia Grape Disease Updates

I just want to remind you about the risk of downy mildew remains high this week. Downy mildew prefer to produce spores under dark and humid conditions.  We experienced a very wet night on the 23rd (no measurable rain, but RH was 100% for 8-9 hours), and then it was followed by a thunderstorm on the 24th (yesterday).  It was a very short storm with ~90 min total wetness duration, which is a minimum time required for downy mildew infection.  In addition, the night time relative humidity have been high for last few days (>80%), and thunderstorms are in the forecast every day of this week.  Moreover, our berries are probably about one to two weeks away from becoming resistant to downy mildew infection (depends on susceptibility of variety and also when it was in bloom). Thus, please make sure to protect your berries from downy mildew as well as black rot. Picture on the top is a cluster showing downy mildew infection on the tip of a cluster.  The picture below is a close up of ano

Luna Experience had a 10-day REI for cane work activities ("cane tying, turning, or girdling",  for other activities, REI is 12 hours); however, it has been changed to 5 days this year.  If you have Luna Experience, and would like to take an advantage of this reduced cane-work REI, make sure to have a new label.  You can download a copy from this link. As usual, please read and follow the label! 

A storm went through our area and resulted in several wetness events.  The longest one was about 11 hours of wetness with an average temperature of 68F.  It was a disease infection event for black rot, Phomopsis, downy mildew, and Botrytis.

A series of rain event started around 9:30 AM on June 6th, and continued on until about 2AM on June 8th at Winchester.  Thus we had a wetness event for about 40 hours with an average temperature of lower 60F (~63F).  It was long and warm enough for Phomopsis, black rot, downy mildew, and Botrytis.  If you are planning for fungicide application to reduce the risk of on-going infection of downy mildew or black rot, please refer to this post , or PMG, or my workbook (PMG and workbook are listed under "Resources").  Looks like chances of rain remain high for next few days across the state. FYI: Because we have seen downy mildew in our vineyard since last week, we applied Prophyt (a phoshite material) and Ranman ( cyazofamid) yesterday morning.  A phosphite material and cyazofamid has a kick-back activity and a protective activity against downy mildew, respectively.  (Note: We did not apply a material for black rot, because it may interfere with some of our experiments.)

Winchester area received a series of thunderstorms from 3:00 PM yesterday, and relative humidity remained high (>90%) until 9:00 AM this morning.  Thus we had a wetness event of 18 hours with an average temperature of 66-67F.  It was warm and long enough for Phomopsis, black rot, downy mildew, and Botrytis infection.