July 16, 2009

Instances of late blight on tomatoes recently were found in Laurel and Larue counties and could be more widespread. Kentucky vegetable growers should regularly scout their potato and tomato plants for this disease, said Kenny Seebold, extension plant pathologist in the University of Kentucky College of Agriculture.

The recent finds of late blight are atypical in Kentucky, where the disease is rarely found. When the disease is present in the state, it usually occurs later in the growing season.  Late blight can devastate crops given the right conditions of cool, wet weather.

"This disease looks a lot different than what growers are used to seeing," Seebold said. "Leaves of infected plants will die and wither quickly.  Unlike most diseases, which begin at the bottom of  the plant and spread upward, this disease can infect the whole plant or begin at the top of the plant."

It is unknown how the disease came into the state, however, late blight is widespread on potatoes and tomatoes throughout the Northeast this year. The disease in that area was traced back to a transplant supplier of several major gardening centers. It is possible Kentucky gardeners purchased transplants from the same supplier or the pathogen traveled to Kentucky from infected areas.

"We do know that we have experienced multiple spells of cool, wet weather recently that would have been ideal for late blight development," Seebold said.  

In addition to scouting, growers may want to apply preventive applications of fungicides containing either chlorothalonil or mancozeb.

"These fungicides will function well, unless we hit long periods of late blight-favorable weather, or if the disease is active in a field.  In these cases, we'll need something stronger," he said.

Seebold encouraged growers who suspect late blight or see anything out of the ordinary on their plants to bring samples to their local extension office for UK plant pathologists to diagnose.