Monday, June 27, 2011

Disease risks from today's rain

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 outside of 66-day PHI, you can mix it with mancozeb product to add extra protection (for both infection and fungicide resistance).

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