Late blight has been found in tomatoes in Middlesex County on August 8, 2025. The identified area was small, but the risk of late blight should be considered high, especially for fields using overhead irrigation reports Amanda Tracey, Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA). 

Samples will be submitted for strain ID. The late blight strain identified in the last few years and in potatoes this year was US-23, which is susceptible to Ridomil (metalaxyl-M). Reports from tomatoes have been documented in New York State and are confirmed US-23 as well. See USABlight for a current outbreak map.

If you haven’t already applied a late blight-specific fungicide, you should do so now. To ensure new growth is protected, continue to use a late blight fungicide on a regular interval, ensuring you are rotating FRAC groups. Visit the Ontario Crop Protection Hub to view registered late blight specific products on tomatoes. Review the CropIPM tomato late blight entry can be found at this link.

Source:  ONVegetables August 9, 2025 blog