Aroostook County potato growers should watch plants closely for late blight symptoms, crop scientists said Friday.
High heat and humidity, followed by wet weather, make ideal conditions for the disease, according to the University of Maine Cooperative Extension’s most recent Potato Pest Alert.
Late blight is a fungal disease that affects potatoes and tomatoes, and can cause widespread crop destruction. The disease hasn’t yet been reported in Maine, but spores were detected across Aroostook County last week. Farmers need to take action to protect the crop, specialists said.
“While this is not out of the ordinary, [the spores’] early presence is a concern given the long season ahead,” extension scientists said. “All growers who have not begun a fungicide spray regimen should do so and stay on a five-day spray schedule for the time being.”
Late blight is caused by Phytophthora infestans, a fungus-like organism that can infect potatoes and tomatoes. It causes discolored spots on leaves and in potatoes, according to the extension publication “Potato Late Blight.”
Spores travel through the air, but don’t live in soil. Growers can combat the disease with fungicide spray.
The extension scientists publish the pest alert weekly throughout the growing season with input from technician Sean McAuley, Pest Management Specialist James Dill, Plant Pathologist Alicyn Smart and integrated pest management technician Griffin Dill. The report contains pest and disease data, along with grower recommendations, for each potato growing region.
Though it’s early in the 2025 season, hot and humid weather has spurred plant growth, the scientists said. Humidity can breed pests, and temperature fluctuations from the heat, followed by cold and wet conditions, can cause wilted or crinkled leaves on young potato plants.
Extreme heat can also cause sunburn on plants, said Caleb Goossen, crop specialist for the Maine Organic Farmers and Gardeners Association, in his pest report issued June 27.
To protect against sunburn, plants should have an adequate supply of water, and full plant canopies should be encouraged, he said. And, because late blight spores have been found, growers need to watch plants closely.
“As of now, we don’t have reason to think there are active infections on plants in the state, but this early spore detection is perhaps a beneficial shock to the system, reminding folks to keep on the lookout for disease symptoms,” Goossen said.
Some insect pests have been detected throughout The County and in central Maine.
Colorado potato beetles are most active in northern and central Aroostook, while aphids are more active in southern Arootook and central Maine, according to the Extension.
Potato leafhoppers are too low in numbers yet to be worrisome, Goossen said.
