Virginia Grape Disease Updates

Winchester area received precipitations from thunderstorms went through yesterday around noon; however, the rain lasted only 30-40 min and dried up very quickly.  Thus, it was not a significant rain event for any disease development.

We had thunderstorms went though yesterday afternoon in Winchester area.  It started around 2 PM, lasted about 20 min, then another one hit around 3:30 PM to 3:50PM.  However; the air was very dry for last few days, and it seems that leaves dried up very quickly after the storm.  Thus, I think it was not good enough for any pathogens to cause disease. On the other hand, the information is just for our area and your vineyards might have experienced a longer wet event.  Downy mildew pathogen needs only about 90 min to cause infection under the optimal condition (about 68F).  Please check with your local weather service. In addition, if the night time relative humidity is high, say above 85% or so, the condition will favor the pathogen to produce spores.  Based on the weather record, I see such conditions 4-5 days per week on average in the past few weeks.  In the other word, even though we have not received a rain event that can be an infection event...

First time in a few weeks, it has been a weekend with no chance of rain.  But there are some chance of rain (~30%) from Tuesday to Thursday.  We are getting close to the end of the critical time for berry infection by black rot, downy mildew, and powdery mildew, thus please be on top of the situation.

Winchester area received an intermittent rain event from 6:00 AM to 4:00PM yesterday.  The relative humidity stayed high (>90%) until 5:00PM.  Thus, this event accounted for approximately 11 hours of wet event with the average temperature of 74F.  It was long and warm enough for Phomopsis, black rot, and Downy mildew infection event. Thank you very much for those of you who made to yesterday's meeting.  We will have a vineyard meeting tonight at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

Winchester area received a thunderstorm starting around 7:30PM last night.  It lasted only 30 min or so, but the relative humidity stayed high (>90%) until 8:00 AM today.  Thus this event was 12.5 hours of wet event with the average temperature of ~73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew. We will have a vineyard meeting at Rappahannock cellars tomorrow from 11AM.  Also, we will have another meeting at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

If you grow Concord and Noiret grape, please be advised that Revus Top (mandipropamid + difenoconazole from Syngenta) may cause phytotoxicity on these variety. The symptoms are light yellow colored scorched (dead) tissue in interveinal area of leaves, and also some deformation of leaves.  Please check this note from Cornell .  We have been testing Revus Top with our Chardonnay in WInchester for two years, but I have not seen any damages on our vines. We will have a vineyard meeting tomorrow from 11AM at Democracy Vineyards .  If you have time, please stop by.

Winchester area received precipitations from thunderstorms yesterday.  It started around 3:30PM and lasted until 7:00PM.  The actual amount of precipitation was not high (0.05 in) compared with other northern VA regions where a severe thunderstorm warning was issued, but since the ending part of the thunderstorm hit during the evening, the relative humidity was high (>90%) until 2 AM or so.  Thus, it accounted for 11.5 hours of wetness with the average temperature of 73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew. We are still having chances of rain (40-60%) until Monday.

Winchester area received rain from 4:40 AM and a series of rain went through our area until 2:20 PM (0.11 in), the relative humidity was high (>90%) until 4:40 PM, thus, we had about 12 hours of wet event with the average temperature of ~63F.  It was warm and long enough for Phomopsis, Black Rot, and Downy Mildew. We are also expecting more rain during the weekend.  The chance of precipitation (by thunderstorms) is 30-40% throughout the state during Saturday and Sunday.  I think most of us are still in the critical period for berry infection by black rot, downy mildew, and powdery mildew (bloom to 4-5 weeks after bloom).  Please check your spray program and local weather to make an adjustment, if necessary.

It seems like there is a chance of rain starting tonight and all day tomorrow.  I was waiting to see if it changes, but now the chance of rain is near 100% for northern VA, and it is lower for the central and southern VA (about 50%).

Winchester area had thunderstorm yesterday from 12:40 PM to 3 PM (0.27 in), the average temperature was around 72 F.  The relative humidity were low after the storm, thus it accounted for about 3.5 hours of wetness.  Then, another drizzle hit us during 3:20 AM to 4:20 AM (0.02 in), and the RH was high (>90%) until 6:20 AM.  The average temperature during this 3 hour wetness event was 59F.  Since both were relatively short and relatively warm, the risk of downy mildew is the major concern. As I noted yesterday, we are having hot humid early summer which is a conducive condition for powdery mildew.  Here are today's pictures from our untreated vines that started to show the development of powdery mildew (click the picture to see a larger image).  Please scout your vineyards especially the location where leaves are shaded.  Powdery mildew pathogen prefer to thrive under diffused sunlight conditions. This is a close-up of powdery mildew pathogen...

Winchester area received isolated rain events yesterday (6/5/10).  The intensity of the rain varied by area, thus, I'm just giving a general idea.  Based on the record, we had rains between 1-3PM and 7-10PM; however, the events were composed of a series of very light rains (less than 0.01 inches), the relative humidity was low (70-80% range), and temperature was high (mid-80's to mid-70's).  Thus, even though we could have a chance of a long wetness period, my guess is that leaves were not wet long enough for many fungal pathogens (Phomopsis, black rot, and downy mildew) to take advantage.  On the other hand, this humid hot cloudy condition may be ideal for powdery mildew development.   We are still having a chance of rain this afternoon.  It seems like northern VA will receive some thunderstorms.

The situation has not changed yet.  We are still expecting some thunderstorms in the state. The chance of precipitation is somewhere between 30-50% throughout the weekend. Winchester area received about 0.02 inch of rain yesterday afternoon.  It only lasted about 1 hour, thus it was not a critical disease event.  Since most of our berries are still in the critical period for downy mildew, black rot, and powdery mildew.  As I have been discussing in various vineyard meetings, black rot requires a certain length of wetness in order to have an infection.  With the optimal condition (~75F), it requires 6 hours.  Downy mildew takes less, about 90 min.  Powdery mildew does not require rain.  Thus, with thunderstorms, it is important to know how long it lasted.  If it was less than 90 min, you probably do not need to worry about risk of diseases.  If it lasted longer than 90 min, then downy mildew comes into play.  If it started late i...

We did not receive any considerable rain during the weekend.  At this point, I am not certain what to believe.  I think the atmosphere is unstable and conducive to create thunderstorms.  We are expecting 30-40% chance of thunderstorm from tomorrow to Sunday. I have seen a small outbreak of mealybugs in our field (please click the picture to see a larger image).  It is a good news for me because I was looking for them, but as you may know, this insect can vector a virus that can cause grape leaf roll disease.  Thus, if you have seen these bugs, please contact me so that I can visit your place to collect samples.  It is very important for us to know which species are present in VA in order to understand the risk of leaf roll spread.  It is a part of on-going leaf roll project and we need more information on this important pest.  Mealybugs are about less than 1/8 of an inch in length and often covered by white hair-like tissues.  Often time, y...