Late blight disease in tomatoes and potatoes could become a problem this summer, so Michigan State University (MSU) Diagnostic Services is offering free late blight testing to Michigan home gardeners and commercial growers.
Free testing will also be available in the College of Agriculture and Natural Resources (CANR) tent from 10 a.m. to noon during Ag Expo, MSU’s outdoor farm show, July 20-22, on Mt. Hope Road in East Lansing.
Because a cool, wet spring has made widespread development of the disease possible in the state this year, growers should become familiar with the symptoms of late blight and other common tomato and potato diseases, according to Jan Byrne, plant pathologist and diagnostician at Diagnostic Services.
“The late blight pathogen can infect both stems and foliage of tomatoes and potatoes,” she says. “The first symptoms are dark green, water-soaked areas. These areas quickly turn dark brown and the plant tissue is killed. In high humidity, growers might notice a fluffy, whitish growth on the underside of the infected leaves.
“The infected areas can grow rapidly in size, causing plant leaves to fall off and eventually the plant dies,” she says. “The tomatoes and potatoes themselves can also be infected.”
Fungicides are available to prevent late blight at garden centers and other stores that sell garden products. Byrne urges home gardeners to read the product labels carefully to make sure such products are labeled for use on tomatoes and potatoes, and have either chlorothalonil or ethylene bisdithiocarbamate (EBDC) as ingredients.
“These fungicides will need to be reapplied frequently, so gardeners should read the instructions on the label,” Byrne says. “But once plants have the disease, they cannot be cured of it, and should be removed and destroyed.”
Though there is no charge for late blight testing (for Michigan residents only), there will be a fee for any other plant disease testing beyond late blight.
More information on late blight and how to submit a sample to the MSU Diagnostic Services laboratory is available at http://www.pestid.msu.edu, or call the laboratory at 517-355-4536.