Late blight of tomatoes not expected to be as severe as in 2009

May 20, 2010

WEST LAFAYETTE, Ind. — After late blight was such a burden in 2009, Indiana tomato growers are wondering if the disease will hit again this year. However, one Purdue University expert said a repeat of last year is unlikely. 

Although late blight should not return as aggressively as it did in 2009, growers still should be aware of symptoms, said Daniel Egel, a Purdue Extension plant pathologist.

“Late blight causes large brown lesions on tomato leaves and stems that under moist conditions are often ringed with the white fungus,” Egel said. “Symptoms caused by late blight may look like other common tomato diseases and, thus, may be easily missed if not sent for accurate diagnosis.”

The late blight in 2009 is believed to have been caused by infectious tomato transplants, which spread to other plants before it could be stopped. The disease infected plants in 39 Indiana counties, causing many headaches to growers.

Growers who suspect the disease can contact a county educator and send a sample to the Purdue Plant and Pest Diagnostic Laboratory. For more information, visit the website at

In the case of confirmed late blight, pesticides containing the fungicide chlorothalonil can be used to help stop the spread of the disease to uninfected plants. Organic growers may find that copper products will slow the spread of the disease.

Commercial growers have many options of fungicides to apply and should refer to the Midwest Vegetable Production Guide for Commercial Growers online at  and the Vegetable Crops Hotline  at  for recommendations and other details.

More information about late blight is available through a Purdue University Extension fact sheet at, or an Ohio State University Extension fact sheet at 

Writer: Jeanne Gibson, 765-494-6682,   

Source: Daniel S. Egel, 812-866-0198,

Ag Communications: (765) 494-2722;
Keith Robinson,
Agriculture News Page