Late Blight—Phytophthora infestans
Late Blight is caused by a fungal-like pathogen. It causes blighting and death of tomato and potato plants during cool, wet weather.
** Late Blight is a very serious disease. If you suspect Late Blight in your garden, please contact the University of Maine Cooperative Extension, Pest Management Office at 800-287-0279 **
Fruit may develop a cottony, white mold growth.
Spots start out pale green and turn brown to purplish-black.
On stems, black and brown spots appear and spread. In high humidity entire veins can be killed quickly.
Brown, leathery spots appear on green fruit on the top and sides. In humid conditions white mold will also form.
In humid conditions a fuzzy mold appears on the undersides of leaves.
Affected fruit often rots as secondary bacteria and fungi enter.
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Identification and Control Information
- Solanaceous, Late Blight—University of Massachusetts Amherst, The Center for Agriculture, Food and the Environment
- Late Blight on Tomato—Cornell University, Long Island Horticultural Research & Extension Center
- Late Blight of Potato and Tomato (PDF)—Maryland Cooperative Extension
- Michigan Potato Diseases: Late Blight (PDF)—Michigan State University Extension
- Late Blight: A Serious Disease of Potatoes and Tomatoes (PDF)—Cornell University Cooperative Extension
- Fact Sheet with Symptoms and Management Strategies—Cornell University
- Gardening After Late Blight (PDF)—University of Maine Cooperative Extension
- Late Blight Management for Fall, Winter and Spring (PDF)—University of Massachusetts Extension
- Managing Late Blight in Tomato and Potato–An Essential Part of Gardening (PDF)—Cornell University
- Late Blight: Frequently Asked Questions by Gardeners, Growers & Consumers (PDF)—Cornell University
More Information
- Disease Prevention in Home Vegetable Gardens (PDF)—University of Missouri Extension
- Controlling Diseases in the Home Vegetable Garden (PDF)—University of Illinois Extension
- An Online Guide to Plant Disease Control—Oregon State University Extension
[Photos, left to right: G.D. Franc, Bugwood.org; Howard F. Schwartz, Colorado State University, Bugwood.org; Howard F. Schwartz, Colorado State University, Bugwood.org; Robert Wick, University of Massachusetts, Bugwood.org; Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org; Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org]