Updates provided by Amanda J. Gevens, Chair, Associate Professor & Extension Specialist, UW-Madison, Dept. of Plant Pathology and Yi Wang, Assistant Professor & Extension Potato and Vegetable Production Specialist, UW-Madison, Dept. of Horticulture
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.