Disease Supplement #7
Late blight has now been confirmed in two counties in WI: Waushara and Adams. This morning, we characterized the genotype of the late blight pathogen collected from a field in Adams County, WI. The genotype is US-23.
US-23 is an A1 mating type with sensitivity to mefenoxam and metalaxyl. This means that application of mefenoxam containing fungicides can be effective in controlling late blight caused by this genotype or strain of Phytophthora infestans.
US-23 was also the type found in early July on tomato in Waukesha County WI. The disease was limited to the one location in July with no further reports through them months of July or early August. US-23 seems to be widespread in the U.S. this summer – with reports in several northeastern U.S.states and in PA.
Recall the other genotypes found in WI in 2010: US-22 sensitive to mefenoxam, A2; US-24 resistant to mefenoxam, A1.
We will continue to provide updates as we learn more about late blight this summer. Please send samples to my lab or leave with the staff at the Hancock Ag Research Station. The more fields sampled, the more thoroughly we can understand the status of the pathogen and aid in management.
Thank you to my graduate students, Anna Seidl and Amilcar Sanchez Perez, for their efforts in this characterization.
Dr. Amanda J. Gevens
Extension Plant Pathologist in Potatoes & Vegetables
University of Wisconsin
Department of Plant Pathology
1630 Linden Dr., Rm. 689
Madison, WI 53706-1598