First reports of tomato late blight in Louisiana, Florida and Maryland

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Late blight has been confirmed on tomatoes in Louisiana, Florida and Maryland. Although a long way from Michigan, last year’s outbreak in the northeast of the United States has been associated with tomato seedlings imported from southern states. Potato and tomato growers should be aware that the disease can overwinter efficiently on discarded potato tubers and that there is an increased risk of late blight the year following an outbreak. Current updates for late blight risk are updated daily at where some images of tomato late blight can be viewed.

From the Potato Disease Management Network on May 16

“Scientists at the Louisiana State University AgCenter recently confirmed the presence of late blight on tomatoes in home gardens in Terrebonne, Lafayette, Livingston and Tangipahoa parishes. Symptoms include black lesions on stems and petioles, blackening of the fruit, and dark, dead areas on the foliage.

“The disease is probably being introduced on infected transplants, so be sure to check tomato plants for symptoms before you buy them,” said LSU AgCenter plant pathologist Don Ferrin.

Experts across the state are working to remedy this situation as quickly as they can, Ferrin said.

“I recommend that home gardeners remove and destroy any infected plants,” he said. “Additionally, as a preventative measure, I suggest they spray their plants on a regular basis with fungicides such as chlorothalonil, mancozeb, copper or a combination of mancozeb plus copper.”

When using the mixture of mancozeb and copper, allow it to sit for about 30 minutes before spraying and stir it frequently, he said, noting that chlorothalonil may be used up to and including the day of harvest, whereas mancozeb cannot be used within five days of harvest.

“Because these fungicides are protectants only, thorough spray coverage is essential for control,” Ferrin said.

“A number of fungicides are available at garden centers,” he said. “Be sure to read the label carefully to be sure the product is intended for use on tomatoes, and apply the material carefully according to label directions.”

“Late blight also occurs on Irish potatoes, so home gardeners may also want to spray them as a preventative measure,” Ferrin said. “Fungicide use rates for tomatoes may not be the same for Irish potatoes, so be sure to check the label.

“With any luck, the warm weather that we’re now experiencing will slow disease development,” he added.”

Dr. Kirk’s work is funded in part by MSU‘s AgBioResearch.

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