Sunday, May 15, 2011

Disease risks from yesterday's and today's rain

We are experiencing a wet weekend, and it seems that is true for many of VA.  In Winchester area, the series of thunderstorms start to pass through the area starting 1 AM in 5/13.  The first estimated wetness event lasted until around 12:40PM on 5/14 (35 h 40 min), with an average temperature of 65F.  It was certainly warm and long enough for Phomopsis, black rot, and downy mildew infection to take place.

Then there was another set of thunderstorms went through the area from 5:40PM on 5/14, then the estimated wetness event ended around 10:20AM on 5/15 (15 h 30 min) with an average temperature of 67F.  Once again, it was warm and long enough for Phomopsis, black rot, and downy mildew infection to take place.  A total amount of recorded precipitation at Winchester airport is about 0.25 inches.

Moreover, as I type this entry in, I hear thunder and see dark clouds moving up from the west of me.  Based on the weather map, it seems that a cold front is passing.

If you have experienced the same type of weather over the last few days, chances are (especially with rapidly growing shoots), you are probably concerned about infections at this point.  Unless, you had a chance to apply materials late last week, which I did not.  Luckily, we have options for both black rot and downy mildew that can be applied after infection event.  Either Phosphorous acid products or Ridomil products are good against downy mildew (if you see active sporulation, Phosphorous acid would be a better choice, considering a risk of fungicide resistance), and either QoI's (e.g., Abound), and mycrobutanil (e.g., Rally) would be a good choice for black rot.

The question is when you can apply them.  It looks like we are looking at a few more rains during next few days...  Hopefully we can find a window (note: typically materials need 2-3 hour of drying time, otherwise rain can wash it off).  I wish you all a good luck.  (and I need one too!)

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