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Late Blight: Grower and Farm Stand Alert, July 5, 2012

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Late blight has just been reported in potato plantings in coastal Maine (Woolwich) and an outbreak was reported in Massachusetts. Conditions for the development of late blight have been very good in Maine and growers should be on the alert to catch any early symptoms on their plants and be ready to apply appropriate control measures. Typical symptoms will be water-soaked lesions on the leaves with fine, white cottony mycelium on the undersides. Infections on the stems appear as dark, almost black lesions. For more photos of the symptoms, go to the Cornell University Extension’s web pages for late blight on tomato and late blight on potato.

Late Blight on Tomato

Late Blight on Tomato; photo by James Dill

Late Blight on Tomato Leaf

Late Blight on Tomato Leaf; photo by James Dill

Late Blight on Potato Leaf

Late Blight on Potato Leaf; photo by James Dill

Late blight spores can travel over 40 miles under the right conditions (wet and warm) and the spread can be very fast. We are encouraging all growers to carefully and regularly inspect their plants for this disease. Please report any suspicious symptoms to the UMaine Extension Pest Management Office at 207-581-3883 or 1-800-287-0279 (in Maine) or e-mail

Samples can be sent to:

Pest Management Office
491 College Avenue
Orono, ME 04473-0279

Samples should be sent in a plastic bag with a dry paper towel to keep them fresh. For the latest control options available for late blight on tomatoes, check out the University of New Hampshire Extension’s fungicide table (PDF).


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