Lesions on fruit and leaves.

Lesions on stems and leaves.

Small lesions on stems and leaves.

News Release Distributed 05/04/10

Scientists at the LSU 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.

Rick Bogren