Scout for Late Blight on Tomato and Potato

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With the current temperatures in the 60’s and 70’s and cloudy skies, conditions are conducive for late blight to occur on tomato and potato. In fact, late blight has been reported on potato and tomato in Alabama recently. Typically, we don’t see late blight on tomato until late summer, but because conditions are conducive, it’s a good idea to scout.

Late blight is caused by the oomycete Phytophthora infestans. It is a fungal-like organism that is particularly good at spreading through air currents. Cool, wet conditions favor this pathogen, if it is present in the area. On tomato and potato, it can be extremely aggressive under these conditions, so it is important to apply preventative fungicides or use resistant varieties. Symptoms on tomato include light brown lesions sometimes with a light green halo. Lesions will attack new growth first, but all parts of the plant, including fruit, can be affected. More information can be found on the tomato late blight and potato late blight disease factsheets.

Late blight on tomato

Late blight on tomato. Photo by I. Meadows

Late blight on tomato fruit

Late blight on tomato fruit. Photo by I. Meadows

If you suspect late blight on your crop, contact your local County Extension agent. You can also send samples to the NC State University Plant Disease and Insect Clinic.

Late blight on potato

Late blight on potato. Photo by J. Ristaino

Written By

Photo of Inga Meadows, N.C. Cooperative ExtensionInga MeadowsExtension Associate, Vegetable and Herbaceous Ornamental Pathology (828) 435-0529 inga_meadows@ncsu.eduEntomology & Plant Pathology
NC State Extension, NC State University
Updated on Jun 16, 2020
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