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Disease risks from yesterday's rain

At Winchester, the second set of rain started at 4:00 pm on 5/12/10 and then we had several short showers during the night.  In the end, the relative humidity was high (>90%) until 11:00 am on 5/13/10.  The average temperature was 64F, starting with higher temperature (72F) and ended lower (55F).  The total amount of precipitation was 0.08 in.

Thus, we had about 18 hours of wet event.  The temperature during 12th was close to the optimal temperature for downy mildew.  As I mentioned in the previous post, we (Winchester) had a potential event for downy on May 3rd, so, I think this rain gave the fungus a good opportunity.  Also, it was high risk event for black rot and Phomopsis.

We are expecting to have more rain events during the next week throughout VA.  Plus, I think most of us are expecting bloom very soon.  The period between bloom to 4-5 weeks after bloom is the critical time for berry infection by downy mildew, black rot, and powdery mildew.  It is unfortunate that rain is coming at the bad moment, but please stay on top of it.  Please check your local weather closely.  We can relax the spray schedule, once the critical period is passed.

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