Sunday, July 3, 2011

Disease risks from today's rain and Botrytis reminder

Winchester area received rains this morning from around 2:30AM until 4:00AM.  Then the RH was high (>90%) until 8:30AM or so.  Thus, it accounted for 6 hours of estimated wetness with an average temperature of 70F.  It was Phomopsis, black rot, and downy mildew risk event.  We are about to exit from critical period for berry infection by black rot, downy mildew, and powdery mildew. 

I just finished my second cover after bloom for my trials yesterday (just in time for the rain :) ).  There are many powdery mildews and a hint of downy in my vineyards.  I hope that you have clean clusters up until this point.  After this critical period, you can relax a bit. 

Also, although it typically requires a longer wetness event in the field, Botrytis can cause infection under the same condition as we seen today.  Probably because of humid nights we experienced in the last two weeks, I have already seen development of Botrytis on our Chardonnay clusters.  Plus, I have heard from others that they have also seen Botrytis here and there.  As for the management, it is important to protect clusters at bunch closure because this is the last opportunity to deliver the material inside of the cluster.  This is especially true for tight-cluster varieties like Chardonnay, which was at bunch closure stage at our station when I checked yesterday.  Then it is also recommended to protect at veraison because there are many spores in the are around that time of the season.  Botrytis can cause diseases on many different hosts including Strawberry and onion, thus, there are many spores floating around the air, but if it infects berries, the source of inoculum will become within a canopy or within a vineyard, and as you can imagine, the risk of disease will be high.

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