Late Blight on Tomato

Tom Creswell and Gail Ruhl, Plant and Pest Diagnostic Lab, Purdue University

We have had several questions pertaining to recent reports from the Northeast on Late Blight on tomato.

Tomato plants infected with late blight (causal organism Phytophthora infestans) were shipped by an Alabama-based company to large retail stores throughout the Northeast region of the country, from Ohio to Maine. So far the disease has been confirmed this year on tomatoes in Alabama, Connecticut, Delaware, Georgia, Kentucky, Maine, Maryland, Massachusetts, New Jersey, New Hampshire, New York, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, and West Virginia (as of August 8th, late blight is now also confirmed in Indiana).

Late blight is a very contagious disease that infects members of the nightshade family (tomatoes, potatoes, sweet peppers, etc.). While the disease is not uncommon in home gardens it is rather unusual for tomatoes to be infected this early in the growing season.

Since there are many look-alike diseases on tomato leaves identification requires microscopic examination, not visual determination. Suspect samples may be submitted to the Purdue Plant and Pest Diagnostic Lab for confirmation.

Two pertinent links:

Late Blight on Tomato Plants at Local Large Stores in Most States in the Northeast

Tomato Diseases and Disorders (pdf file)

Click image to enlarge

Late blight symptoms on tomato fruit

Late Blight Sporulating on lesion on the underside of tomato leaves