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Disease risks from weekend's rain

Finally!  Winchester area had decent rain events over the weekend.  The rain event started from 7:40PM on Thursday (we missed the one earlier that day, although other northern VA area received thunderstorms), and a series of rain went pass throughout last Friday.  The relative humidity was above 90% until 8:20PM on Friday.  It resulted in almost 25 hours of wet event with an average temperature of ~74F.  It was a long and warm enough for downy mildew and Botrytis.  Then we had several rain events on Saturday and Sunday.  None of them are very long, but long enough for downy mildew to cause infection.

Once again, we had a dry summer and the threat from downy mildew may or may not be the primary concern.  But if you still have a few more weeks to go until the harvest, please keep your eyes on younger foliages (typically you find them on the upper part of the canopy) for the sign of downy mildew.  It can go from a trace level to an outbreak in a short time, and heavy infection can cause defoliation on leaves.  If you knew you have some downy prior to this series of rain over the weekend and your leaves are not protected, you may want to consider Phosphorous acid products such as Prophyt which should give you a good curative and protective activity against downy mildew (+ short PHI).

Also, there are chances of rain (30-70%) on this Wednesday and Thursday.


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