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Thunderstorms forecasted for this weekend

The situation has not changed yet.  We are still expecting some thunderstorms in the state. The chance of precipitation is somewhere between 30-50% throughout the weekend.

Winchester area received about 0.02 inch of rain yesterday afternoon.  It only lasted about 1 hour, thus it was not a critical disease event. 

Since most of our berries are still in the critical period for downy mildew, black rot, and powdery mildew.  As I have been discussing in various vineyard meetings, black rot requires a certain length of wetness in order to have an infection.  With the optimal condition (~75F), it requires 6 hours.  Downy mildew takes less, about 90 min.  Powdery mildew does not require rain.  Thus, with thunderstorms, it is important to know how long it lasted.  If it was less than 90 min, you probably do not need to worry about risk of diseases.  If it lasted longer than 90 min, then downy mildew comes into play.  If it started late in the evening and the relative humidity is high (> 90%) for more than 6 hours, then depends on the temperature, black rot could have an infection.  For the details on infection conditions, please refer to my vineyard notes.

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