Courtesy Agricultural Research ServiceThe fungal disease late blight is responsible for the Irish Potato Famine of the 1840s.Late blight was confirmed in a potato field in Portage County, Wis., July 18, but it's not the same strain as has been found elsewhere this year.
Until now, all of the genotypes of Phytophthora infestans have been US-23, according to a University of Wisconsin grower e-newsletter.
The genotype found in Wisconsin was US-8, a type that dominated the 1990s and that can infect both tomatoes and potatoes. US-8 also was found in Portage County in 2013.
US-23 can infect both tomatoes and potatoes as well.
The US-8 genotype is resistant to mefenoxam/metalaxyl fungicides, which has been associated with the A2 mating type.
The mating type is a further means that pathologist use to narrow the genetics of the late blight organism.
Amanda Gevens, a University of Wisconsin Extension plant pathologist in potatoes and vegetables, recommends preventive fungicide treatments for tomato and potato fields in Portage County or within about a 50-mile radius.