The Ontario Potato Board reports that for the second time this season, late blight spores have been detected in their spore traps in the Shelburne and Alliston areas. Late blight symptoms have not been detected, but it means that spores were present in the area.
Growers across Ontario should be scouting their crops frequently. Late blight was detected in south central Michigan on July 5 (US-23 genotype) and July 25. Now that many areas have received significant rains, the environment is better for infection and symptom development.
To summarize, no late blight has been found in Ontario yet this season, to my knowledge. However, the presence of spores of the pathogen (Phytophthora infestans) mean that with the right environment, inadequately protected host crops (tomato, potato) could be at risk.
Thanks to Dr. Eugenia Banks and the Ontario Potato Board for the spore trapping results. Their project is supported by Growing Forward 2.