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Disease risks from yesterday's rain

At Winchester a series of rain started around 11:40 am and lasted until 6:40 pm resulting in 0.1 inches of precipitation.  The average temperature during this period was about 50.5 F.  Since the rain ended late in the evening, relative humidity stayed high (>90%) until 8:40 am today.  Thus, in reality, leaves were probably wet for 21 hours or so, with the average temperature of 55 F.

This accounted for moderate risks for both Phomopsis and black rot.  Although there were long enough wet period for downy mildew, the temperature might have been a low side of the activity for the downy mildew fungus, thus, I would rate a low to moderate risk for downy.  Plus we had long enough wet period for the powdery mildew fungus to shoot out ascospores.

We had a potential downy mildew infection period back in May 3rd.  This is about the time you will start to see the symptom development (click the picture to see a larger image).  Please check your vines closely and adjust your spray schedule if needed.

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