Wisconsin Potato and Vegetable Growers Association

Late Blight Prevention and Canadian Update

July 31st, 2023 | Posted in: Crop Updates, News

A Newsletter for Commercial Potato and Vegetable Growers Prepared by the University of Wisconsin Madison Vegetable Research and Extension Specialists


Late blight was confirmed in potato in Alliston, Canada on July 17, 2023.  This is Simcoe County of the Province of Ontario. A sample of infected leaves was sent to Dr. Jean Ristaino’s lab at North Carolina State University where it was determined that the pathogen, Phytophthora infestans, was of the US-23 genotype.  Dr. Eugenia Banks, the Potato Specialist at OMAF, further added that late blight was also confirmed on potato and tomato on July 25, 2023 in commercial plantings in Mauricie in the Province of Quebec.  All infected plants were destroyed.

The US-23 clonal lineage/genotype/strain type is generally still sensitive to phenylamide fungicides including mefenoxam and metalaxyl.  Eugenia told me that in addition to metalaxyl (ie: MetaStar) and mefenoxam (ie: Ridomil), mandipropamid (Revus), cymoxanil (Curzate), and oxathiapiprolin (Orondis) were all performing well.

Attachments:  1) I’ve included a Canadian report from July 17 for your further information. 2) Listing of fungicides for potato late blight management in Wisconsin.  A complete listing of fungicides can be found at our Commercial Vegetable Production in Wisconsin A3422 Book:





Amanda Gevens
Chair, Professor & Extension Specialist
Interim Administrative Director of the Wisconsin Seed Potato Certification Program
Fritz Friday Chair for Vegetable Production Research
Plant Pathology Department
1630 Linden Drive Room
University of Wisconsin-Madison
Madison, WI 53706
[email protected]/608-575-3029

Potato & Vegetable Pathology Research and Extension

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