The question of eating or canning tomatoes from plants infected with the late blight fungus has been frequently asked question this summer. I’ve compiled information from colleagues and food safety experts from states experiencing the late blight epidemic. Healthy, un-blemished fruit can be safely eaten or canned. Canning should be done immediately after harvest because even healthy-looking fruit can still be infected and develop lesions while in storage. It may be best to freeze unblemished fruit from infected plants.

Fruit showing any symptoms of infection should NOT be eaten or preserved either by canning or freezing. Plant pathogens cannot infect people, and the late blight fungus does not produce a toxin that can make people sick, as some other plant pathogens may. But, infected fruit may have an off flavor.

The USDA Complete Guide to Home Canning (1994 ed.) recommends that canners select onlydisease-free, preferably vine-ripened, firm tomatoes for canning. Food safety experts explain the fungal infection may raise the pH of the tomato flesh to a level unsafe for canning and/or make the tomato more susceptible to other pathogens. Secondary organisms that could
cause food-borne illness may also colonize infected fruit. Dr. Luke La Borde, the Food Safety Specialist from Penn State, has compiled an excellent guide about the safety of blight affected tomatoes and potatoes. The guide can be found at: http://foodsafety.psu.edu/LateBlight.htm

So, in summary: Tomatoes showing signs of late blight disease should not be
eaten or canned-including tomatoes with only minor lesions. And, un-blemished tomatoes from affected plants can be eaten or processed but should be eaten or processed as soon as possible after harvest as they are at higher risk for developing lesions.

-Cheryl A. Smith, PhD
Extension Professor
Plant Health Specialist

NH Department of Agriculture, Markets & Food
September 23, 2009 Weekly Market Bulletin