Grape Disease Risk Summary 9/28 – 10/5/2022

Here’s a snapshot from the last week, showing the number of days with the risk of each disease: Ph = Phomopsis, PW = Powdery mildew, BR = Black rot, and DM = Downy mildew. This information was made available through Wine Board-funded the Sentinel Vineyard project.

The image above is just a summary of the past 7 days. Please visit https://newa.cornell.edu/ to obtain more detailed information. You can check daily weather data as well as disease and insect pest model results including forecasted risks. We paid the annual fee so that growers in Virginia can freely access NEWA.

It looks like we had a nice dry week. Despite hurricane Ian, many locations showed a small number of days with high downy mildew risk, probably because the overall risk of downy mildew in the previous 7 days was low in many locations.

If you still have clusters to harvest, here’s a list of short PHI material. At this point, target diseases are downy mildew and late-season rots.

The list of short PHI (< 7-day) materials is here (pdf format).

The risk information above is just output from the model, and the spray decision needs to be based not only on the weather condition but on the cultivar and history of the disease(s) in your vineyard.

If you are in an unfortunate situation where downy mildew was well established (i.e., you can see it everywhere), please use captan or copper to keep your healthy leaves protected. Clusters are resistant to new infection at this point, but if you do not protect leaves, downy mildew can defoliate leaves. Please do not use Revus, Ranman, or Ridomil which are prone to develop fungicide resistance.

This is the last disease risk post for the season. However please keep eye on this blog since there will be announcements for meetings and other events coming soon!

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