Virginia Grape Disease Updates

It seems like the rest of VA received a little more rain than we did, but we received a shower in the monring of June 28th from 4:30 AM to 6:00 AM or so.  Then the relative humidity was above 90% until 8:30 AM or so, thus it was 4 hours of an estimated wetness event with an average temperature of 70F.  It was a light infection event for Phomopsis, and an infection event for downy mildew.  As I noted yesterday, Winchester area is experiencing several consecutive nights with high relative humidity (including last night), which promote spore production of downy mildew.  In addition we have been receiving showers several times during past 10 days or so.  I have not seen an outbreak of downy mildew in our 'unsprayed' vines yet, but I observed many symptoms (yellow spots with brown dots, often called 'oily spots') on upper surface yesterday.  For pictures of downy mildew symptoms, please click here.

Winchester area received drizzle during early morning today.  It started around 3 AM and the RH was high until 9:30 AM or so.  It was 6.5 hours of an estimated wetness with an average temperature of 64F.  It was long and warm enough for Phomopsis, black rot, and downy mildew infection risks. Since we received a series of rain after nights with high relative humidity, thus some of you might experiencing development of downy mildew.  Most of us are probably at the tail end of the critical time for berry infection (4-5 weeks since bloom).  If you see the beginning of downy mildew development, my recommendation is a use of phosphorous acid material such as Prophyt or Agri-Fos.  It has some kick-back activity (please note that it won't kill actively growing colonies, it works when you apply a period between infection and establishment ~ up to 3-5 days after infection), and a relatively low risk for fungicide resistant development.  If you are still outsid...

Winchester area received rain around midnight on June 21st then although there were not much of precipitations, there were a few showers passed the region, and the relative humidity was high (>90%) until around 9AM.  It was 9 hours of an estimated wetness event with an average temperature of 68F.  Then there was another rain event started 11:15PM until 8:15AM on 22nd (today).  It was 9 hours of an estimated wetness with an average temperature of 73F.  Both events were infection risk events for Phomopsis, black rot, Botrytis, and downy mildew.  In addition, we are having about a week of consecutive high humidity warm nights that promote downy mildew spore production. FYI: I'm still at the conference, if you would like to contact me, email is the best way.

We are having a wet Monday.  It started raining on Saturday (luckily, after I finished the most of treatment sprays), but we had a break from rain yesterday morning.   For Winchester, rain started around 8PM Saturday, and the relative humidity was > 90% until 11AM on Saturday.  Thus, it was 15 hours of an estimated leaf wetness period with an average temperature of around 73F.  It was long enough for Phomopsis, black rot, and downy mildew.  Since it was a long event, it was probably an infection event for Botrytis as well.  In addition, we are experiencing nights with high temperature continuously, which promotes downy mildew sporulation. As I mentioned a few times this year, these isolated thunderstorms are very difficult to predict and measure.  For example, our vineyards start received rain from 4PM on Saturday, but the city of Winchester which is only 6-7 miles away was bone dry.  Plus the rain seemed to come out from nowhere.  ...

Once again, it looks like Winchester area received a little less precipitations than other northern VA regions, but finally there were some moisture came to the ground.  On Thursday the 16th, we received short showers here and there, but the major event did not arrive until 10:30 PM when we received measurable rain, then the relative humidity was high until 9:00 AM on Friday the 17th.  Thus, it was 13.5 hours of estimated wetness hours with an average temperature of 65F.  Thus, it was Phomopsis, black rot, and downy mildew infection event. I saw thunders, but we did not receive precipitation on Friday night; however, the relative humidity stayed high for a whole night.  That means that we had two consecutive nights with a high (>90%) relative humidity with temperature in mid-60's.  These warm nights are favored by downy mildew, and they tend to produce spores under these conditions.  Thus, the next rain event in the near future could be a high risk eve...

We will have a vineyard meeting tomorrow at Ducard vineyards from 11AM.  If you have a time, please stop by.  I will cover disease update, Tony and Tremain will cover viticulture updates. 40 Gibson Hollow Ln., Etlan (Madison Co.) VA 22719 http://www.ducardvineyards.com/ Directions : Take Rt 29 to Madison, VA, then Rt 231 north and proceed to Etlan. Turn left on Rt 643. Proceed 2.5 miles to a right on Rt. 719 (Gibson Hollow Ln.). Entrance is on the right Contact :  Kenner Love, Rappahannock County Cooperative Extension (540) 675-3619

I was driving up and down on I-81 this weekend and went through severe thunderstorms several times.  I was hoping to see some precipitation around Winchester, however, thunderstorms in Saturday morning were the only ones which really accounted for measurable precipitations.  Thus, for us, the rain started around 1:30 AM on Saturday the 11th (~0.12 inches), then lasted until 5:00 AM or so.  The RH stayed above 90% until around 8:15AM.  This accounted for almost 7 hours of wetness event with an average temperature of 73F.  This was a potential infection event for Phomopsis (light infection), and was a borderline case for black rot.  Also, it was good for downy mildew infection as well. I am aware that many of you received more rains than we did.  Please check your local weather to see what may happened in your vineyards.

Winchester area received thunderstorms last night from 5:30 PM to 8:00 PM.  However, it only rained about 10 min, and the amount of precipitation was less than 0.01 inches.  Thus, for us, it was not significant enough to be any disease risk.  However, these rains from isolated thunderstorms vary considerably even over a small geographic area.  Please make sure to check your local weather record.  We are expecting to see some more rains tonight and on Saturday.  We have been pretty dry, so, we will see...

Thunderstorms went through Winchester area around 4:30AM this morning.  The relative humidity was high (>90%) until 8:00 AM or so.  This short estimated wetness event with an average temperature of 63F was too short for most of pathogens, except for downy mildew.  [However, since we had two weeks of hot dry weather, the overall risk of downy could be low.]