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Disease risks based on Sunday-Monday rain events

At Winchester area, the second series of rain started around 5:20 pm on Sunday, then it continued on and off until around 8:30 pm on Monday with about 0.17 inches of precipitation.  Thus, there was about 27 hours of wetness with average temperature of 58F or so.  It was long and warm enough for Phomopsis, and Black Rot to cause infection.  Also, these rains from Saturday probably initiated ascospore release of powdery mildew.  (Powdery mildew does not require water for its infection, but it requires water to release ascopsores from its over-wintering structure.)  The average temperature was low for downy mildew, but between noon to 5 pm Monday, we observed 60-65F while it's raining.  Thus, it might be accounted for downy mildew as well.

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Disease risks from yesterday's rain

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.

Recent downy mildew risk events

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EPA is reviewing captan

Captan, which we use extensively to manage downy mildew, Phomopsis, ripe rot, and other grape diseases, is currently under review by the EPA. In order to keep captan as one of our tools to control grape diseases,  please respond to the EPA's registration review page to post your comment  (will open the EPA page). With increasing cases of fungicide resistance with newer products in our region, it is very important for the majority of commercial grape growers located east of the Rockies to keep older multi-site materials such as captan to be used as a backbone of the spray program.  Also, please forward the message to other producers and stakeholders who should respond to the need for this fungicide in our industry.