Virginia Grape Disease Updates

A rainy weekend brought our area two estimated wetness periods (19h with 73F, and 20h with 64F), plus additional 30h+ hours of high humid condition (RH>90%) (note: some of you might have ended up with 50+ hours of wetness period.  We only had about 3 hours where RH dropped below 90% on Saturday).  The wetness periods were infection events for Phomopsis, black rot, downy mildew, and Botrytis.  (note 2: your vines should be over with a critical period for berry infection for black rot and downy mildew.) In addition, the extensive humid condition probably favored downy mildew spore production.  As you know, severe downy mildew infection can cause defoliation.  If you are debating whether you should apply a downy mildew material or not, you can scout for downy mildew symptoms.  At this time of the year, it tends to show up on younger (= upper part of the canopy) leaves because these are more susceptible than older leaves. At this point, people often use ...

Thunderstorms went through yesterday in Winchester area; however, air was dry (RH<80% even during the rain), and the sun came up soon after that, thus, leaves were probably dry soon after the rain.  It was probably not a disease risk event.  We are expecting to see more rain this afternoon.

Someone in MN lost his 40,000-square-feet lawn by a misapplication of herbicide.   I think this is a good reminder for us all to read and follow the label.

The second rain event on Sunday night ended up with about 10.5 hours of estimated wetness with an average of 70 F.  It was infection event for Phomopsis, black rot, downy mildew, and Botrytis. Also, we had another warm and humid (RH >95%) night.  As I mentioned the other day, these conditions are favored by downy mildew pathogen to produce spores.

It looks like we have thunderstorms every weekend! There were a few line of rains went through Winchester area, and two risk events were observed.  One was on Saturday morning with 8.5 hours of wetness with 68F, and the other one is on-going from last night with 5+ hours with 70F.  The first one is a risk event for black rot, Phomopsis, downy mildew, and Botrytis.  I will update for the second event, but from the look of outside, the humidity may drop very soon. These rains (or high humidity) during night time promote downy mildew to produce its spores.

Rain fall in 8-9 July resulted in 15 hours of estimated wetness event with an average temperature of 72F.  It was infection event for Phomopsis, black rot, Botrytis, and downy mildew. Due to a series of rains we received over last two weeks or so (including a few nasty storms), I started to see downy mildew development in our experimental vineyards.  Please keep eye on them.  We are most likely done with the critical time for berry infection, but it can still cause disease on leaves.

There were two storms on Monday and Wednesday went through Winchester area, but these were too short to count as disease events. Only potential exception is downy mildew, which can cause disease in a short time (90 min or so); however since air dried out very quickly after the storm, these probably did not count as downy mildew disease risk events.

Winchester area received precipitations from another storm that started shortly after midnight.  It was approximately 8 hours of wetness with an average temperature of 68F.  It was infection events for Phomopsis, black rot, and downy mildew, and a borderline case for Botrytis infection. It looks like we have a chance of a thunderstorm (30-45%) almost every day this week.  Hopefully next ones are not as bad as previous ones.

Winchester area received a severe storm in lat Friday night, and that brought us an estimated 11 hours of wetness with an average of 68F.  It was risk events for Phomopsis, downy mildew, black rot, and Botrytis. Nothing major, but we had some damages on our vineyards due to the storm.  I hope your vines were OK. According to the radar, it looks like another storm will pass through tonight.  We will see...