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.
We had another lovely dry week, and no significant risks were observed. However, this is a prime time for Phomopsis activity. Thus, if you see rain coming into your area, it is better to protect your vines. Here’s a link to early-season grape disease management reminders. 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.)
The image above is just a summary of the past seven days. Please visit https://newa.cornell.edu/ 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, you need to prepare your sprays to protect your vines. 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 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.
With incoming rain forecasted during the weekend, I think it is worth protecting your vines this time around, especially if you saw significant growth from when you sprayed last time. We decided not to cover for incoming rains because we did not see much growth since the last spray a week ago. 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.