Wednesday, June 29, 2011

Disease risks from yesterday's rain

It seems like the rest of VA received a little more rain than we did, but we received a shower in the monring of June 28th from 4:30 AM to 6:00 AM or so.  Then the relative humidity was above 90% until 8:30 AM or so, thus it was 4 hours of an estimated wetness event with an average temperature of 70F.  It was a light infection event for Phomopsis, and an infection event for downy mildew. 

As I noted yesterday, Winchester area is experiencing several consecutive nights with high relative humidity (including last night), which promote spore production of downy mildew.  In addition we have been receiving showers several times during past 10 days or so.  I have not seen an outbreak of downy mildew in our 'unsprayed' vines yet, but I observed many symptoms (yellow spots with brown dots, often called 'oily spots') on upper surface yesterday.  For pictures of downy mildew symptoms, please click here.

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