Amanda Gevens, Associate Professor & Extension Specialist, Potato & Vegetable Pathology, Plant Pathology Department
https://wisconsinpotatoes.com/wp-content/uploads/2020/08/August-9-2020.pdf
The Phytophthora infestans pathogen causing late blight that was found in Adams County potatoes earlier this week has been typed as US-23. This type is most typically sensitive to phenylamide fungicides such as metalaxyl and mefenoxam (ie. Ridomil). As such, treatment with a fungicide like Ridomil should be highly effective at this time in WI (presuming that this is the primary type of the pathogen present in the state). In our recent analyses of US-23 isolates from WI, most were still fully sensitive to mefenoxam; less than 10% of isolates showed some tolerance.
Many thanks to Dr. Yu Monica Chen in my lab for the quick lab response to this disease situation. We appreciate this information as it aids in best management of such a potentially devastating disease.
In this issue (linked above) we address updates from N trials on potatoes, updates on potato/tomato late blight; potato early blight; and cucurbit downy mildew.
Cucurbit powdery mildew is beginning to show up in southern and central WI on non-cucumber cucurbit types primarily. Page 244 in our A3422 WI Commercial Vegetable Production guide (link below) can help guide fungicide selections. Hot, dry weather can especially exacerbate this disease. In our recent trials programs including quinoyxfen (Quintec) were especially effective at reducing powdery mildew in pumpkin. In WI, we have documented resistance in the pathogen population to myclobutanil (Nova, Rally).https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3422-2020.pdf
Wisconsin Vegetable Crop Update blog site where you’ll find updates throughout the year.