The outbreak, which is the worst in the region for more than 20 years, has spread from Maine to Ohio, destroying tomato and potato crops.

Phytophthora infestans, commonly known as late blight, is spread by spores, and can destroy a potato crop in just a few days under cool, wet conditions.

The province's potato expert, Eugenia Banks, said outbreaks of late blight have already been detected and controlled in three commercial fields in Grand Bend, Ontario.