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Disease risks from yesterday's rain

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 event for downy mildew.

Of course, I see some rain clouds coming toward our area on the radar.  I was hoping that I can spray this morning...  We will see...

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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

 It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection e...

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.