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Disease risks from yesterday

Yesterday's shower brought about 7.5 hours of estimated wetness duration with an average temperature of 71F around Winchester area.  It was an infection event for downy mildew and Botrytis, and it was a potential infection event for black rot and Phomopsis (although these two diseases are of relatively minor importance at this point of the season).  Once again, I see the risk of downy mildew remains high.  Please scout your vineyards (especially for younger leaves) often to catch early development of downy mildew.

Around this time of the season, I am often asked about the potential impact of a fungicide application on wine quality.  There were several studies where authors detected chemical residues on the must.  It is often practiced to avoid application of sulfur and copper 3-4 weeks prior to the harvest.  It would be relatively easy to do when we have a dry condition, but sometimes (like in 2011), we may just need to do whatever we can to secure yield.  For example, a good air circulation (= canopy management) around clusters is very important.  For late season rots (sour rot, ripe rot, Botrytis and other general rots), captan is often used, and Switch is labeled for both Botrytis and sour rot.

If your concern is downy mildew or powdery mildew, you can also spray only on foliage (i.e., avoid spraying fruiting zone by closing nozzles), since your berries have developed resistant.
  

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