Virginia Grape Disease Updates

July 27-28th were very wet for us.  We recoded two long wetness events (8 hours and 22 hours), which were infection events for Botrytis, downy mildew, black rot, and Phomopsis.  In addition, we had a short rain event that were long enough to be considered as downy mildew infection event. Our major concern would be Botrytis on fruits and downy mildew on leaves.  Please make sure to have protection on clusters against Botrytis.  We do not have any fungicides that work after infection takes place.

July 24 th   Gadino Cellars and Vineyard, Bill and Aleta Gadino owners. Tour Begins:   3:00pm Topics:             §   Disease Management   – Dr. Mizuho Nita, Virginia Tech Grape Pathologist §   Insects Updates - Dr. Doug Pfeiffer, Virginia Tech Entomologist §   Viticultural Update   - Tremain Hatch, Viticulture Research/Extension Associate Location: Gadino Cellars GPS coordinates 38.69073544820042, -78.16712379455566 92 Schoolhouse Road Washington, Virginia 22747 (540)987-9292

Winchester area received a short rain event on the 21st.  It only lasted a short time, but due to that relative humidity stayed high for the whole night.  (i.e., it was a good condition for downy mildew to produce spores)  Then we received rains from about 4 PM yesterday.  It resulted in about 18 hours of wetness with an average temperature of 69F.  It was an infection risk event for downy mildew and Botrytis.   Our Chardonnay is getting close to veraison, so, we probably will think about Botrytis treatment on the next round of application. (As I noted in the previous post, even though it was also events for black rot and Phomopsis, these disease should not cause major damages on your berries at this late in the season, unless you have chronic issue with Phomopsis.)

An extensive wetness event was recorded on 7/12-13 (~30 hours) with a temperature range of upper 60F to lower 70F.  In addition, there was about 9 hours of wetness recorded in 7/14 with an average temperature of 70F.  Both were infection risk events for downy mildew and Botrytis (especially the long one in 7/12-13).  (These were infection events for black rot and Phomopsis, but berries should be resistant to black rot infection and Phomopsis is typically not active late in the season.) (Note: for some reason I was not able to upload this note on time.  Sorry!)

Boy, it's really hard to keep up with rains this year! We had about 10 hours of wetness on both 9th and 10th, and about 9 hours on the 11th (yesterday).  Average temperature were in upper 60F to lower 70F.  These were events for downy mildew, black rot, and Botrytis.  However, as I noted in the previous post, berries should be out from the critical period of infection by downy, black rot, and powdery mildew.  However, with these frequent rains, risk of Botrytis is probably high overall, especially for tight cluster varieties.

We had about 18-19 hours of wetness event in lower 70F in July 7-8th.  It was infection risk event for black rot, downy mildew, Botrytis, and Phomopsis.  At this point, most of your berries are out of critical period for downy mildew, powdery mildew and black rot infection.  Rain today looks like bring another infection events... Also, please keep in your mind about the 66-day PHI of mancozeb products.  Many of early varieties are at or near the limit at this point

We (Winchester area) received a few showers in the past 24 hours, and the longest wetness event was due to a shower passed  around 5 AM this morning.  It resulted in about 10 hours of wetness with an average temperature of upper 60F. It was an infection risk event for black rot, downy mildew, Botrytis, and Phomopsis.  In addition, we received 2-3 showers that resulted in more than 90 min of wetness ( i.e., these showers were downy mildew infection risk events). Our Chardonnay is close to bunch closure stage, thus, we applied Botrytis treatments this morning.  Bunch closure is the last opportunity for us to deliver materials inside of the clusters, especially with variety with a tight cluster, such as Chardonnay.

It looks like we are going to have another wet week... The rain on the 29th was a very short one, but it was enough to make leaves wet for about 10 hours and the average temperature was higher 60F.  It was infection event for downy, black rot, and Phomopsis.  The rain on the 30th was too short for any infection. Once again, the current condition favors development of downy mildew and black rot.  Please do not let something like the picture below happen to you!  (Downy mildew on a cluster, taken from our downy mildew trial.)