Grape Disease Risks 4/27 – 5/3/2023

I hope your vines did not suffer from recent frost events. Based on what I heard from growers, some growers in the Shenandoah Valley suffered minor damage on specific cultivars, and a few suffered severe damage.

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 the Wine Board-funded Sentinel Vineyard project. The downy mildew model is back again (except for the Leesburg station… I will report it to them. Based on the risk output from the nearby weather station, the risk of downy mildew was most likely zero at the location, though.)

Recent (and much-needed) rain events brought a few days with disease risks. Since these were cold rains, the number of days with Phomopsis risks showed up in some locations, especially in the state’s eastern side. It looks like the forecast is relatively dry and warm for the next week, with a slight risk of rain on Wednesday. We will see how it goes.

Here’s a link to early-season grape disease management reminders. 

The image above is just a summary of the past seven days. Please visit to obtain more detailed information. You can check daily weather data and disease and insect pest model results, including forecasted risks. We paid the annual fee so that growers in Virginia could freely access NEWA.

The risk information above is just output from the model to help you understand what happened. However, preparing your sprays to protect your vines would be best. One way to use this information is to adjust your spray intervals. If you see many days with disease risk(s), you may need to shorten your spray interval, or if you missed a material for downy mildew or black rot, you might wish to spray material(s) with kick-back activity. Or you may want to extend your spray interval, if you have not seen much risks as we have been experiencing this year. 

It is essential to understand that the spray decision must be based not only on the weather condition but also on the cultivar and history of the disease(s) in your vineyard.

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