Late blight confirmed in potato in Alliston, Canada on July 17, 2023

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.

More information:

  1. Read the Canadian report from July 17 (PDF)
  2. Listing of fungicides for potato late blight management in Wisconsin (PDF)
  3. A complete listing of fungicides can be found in Commercial Vegetable Production in Wisconsin (A3422), available for download at the UW Extension Learning Store.