Last week, a potato field in Montcalm County, MI, was reported to be infected with late blight. The Phytophthora infestans isolate is the US-23 genotype. This genotype is said to be Ridomil-sensitive, however, treatment recommendations include applying one of the translaminar fungicides listed on LateBlight.org/fungrate.html.
A potato and tomato field in Lagrange County, IN, were reported last weekend to have late blight. The tomato field has been treated with fungicides. The genotype is US23 – A1 mating type, which also is sensitive to Ridomil.
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Source: Michigan State University Extension