New Brunswick's Department of Agriculture, Aquaculture and Fisheries is advising anyone who bought tomato plants at garden centres to check them for late blight.

Tomato late blight

Tomato leaves infected with late blight should be removed and infected plants should be destroyed, the Department of Agriculture says. (Courtesy of Government of New Brunswick)

The disease, caused by the fungus Phytophthora infestans, is not dangerous to humans, but can be "devastating" to crops, particularly tomatoes and potatoes, the department said in a release.

The fungus can produce millions of spores during wet weather conditions, which can infect the plants up to 80 kilometres away by travelling on the wind.

"Because this disease is so devastating to crops, it is important that gardeners recognize late blight and control it before their garden becomes a source of spores that can infect nearby gardens and commercial fields," the department said.

Late blight is the same disease that caused the potato famine in Ireland in 1845 and contributed to the deaths of up to one million people.

The fungus appears on potato and tomato leaves a few days after periods of humid or rainy weather. Dark green water-soaked circular or irregularly shaped spots that may be ringed by a pale yellowish-green border develop.

White, fluffy mould may also develop on the underside of infected leaves and produce spores during humid conditions.

Any infected leaves should be removed. If the entire plant becomes infected, it must be destroyed.

To avoid late blight:

  • Keep foliage as dry as possible.
  • Avoid watering plants in the late evening or early morning.
  • Do not over-fertilize.