Wisconsin Late Blight Update
The late blight collected from potato in Portage County on Friday July 18, 2014 is of the US-8 genotype/strain.
This type is resistant to mefenoxam/metalaxyl fungicides (ie: Ridomil) and is an A2 mating type.
While all other Phytophthora infestans genotypes from the U.S. in 2014, so far, have bee US-23, the US-8 type predominated in the 1990’s and was found in Portage County in 2013.
US-8 is known to infect both tomato and potato (much like the US-23 genotype).
At this time, it is important for potatoes and tomatoes in the Portage County area (plus roughly 50 miles radius) to be preventively managing late blight with effective fungicides. Anti-sporulant fungicides are particularly useful at this time. A 5- to 7-day spray interval is recommended. For production further away from this site, a 7 day program should be appropriate.
There is rain in the forecast for Tues for parts of the state – and then more precipitation forecasted for the week’s end.
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