Late blight causes lesions along the stems of tomato plants.

Late blight causes lesions along the stems of tomato plants. Credit: Meg McGrath

Farmers and gardeners: Late blight has been confirmed in Suffolk County, so watch your potatoes.

The disease, a factor in the Irish famine in the 1840s, has been found in at least six locations on Long Island -- from Riverhead to Mattituck on the North Fork, and in Bridgehampton on the South Fork, according to Meg McGrath, a plant pathologist at Cornell University's extension center in Riverhead.

Commercial farmers and home gardeners should be on alert, McGrath said, because late blight moves quickly. New York State's agriculture department Tuesday issued an alert about the disease.

"They've got to be looking for the disease, they need to notify [authorities] when they detect it, and they need to manage it," McGrath said. "This is a scary thing."

Late blight strikes tomatoes and potatoes, and between 50 and 100 vegetable farms on Long Island could be affected, said Joseph Gergela, executive director of the Long Island Farm Bureau.

It causes black or brown scarring on leaves, and breaks down fruit into a rot.

The disease is especially vexing to organic growers, he said, who can't rely on traditional fungicides to combat late blight.

"They just don't have the arsenal," he said.

So far, Gergela said, the disease hasn't caused much crop damage.

However late blight can be costly even without a major outbreak because the fungicides used to prevent its spread cost as much as $40 per acre, according to Jimmy Zilnicki, 52, a Riverhead farmer who has been growing potatoes since he finished high school.

Zilnicki said that he spends up to $8,000 each time he treats his potatoes, totaling as much as $50,000 over the growing season.

"It's like an insurance policy," he said. "You've got to use it. You've got to spend the money as a protectant."

Late blight has been detected on Long Island every year since 2009, officials said.

One positive: the disease thrives in cool, damp weather, and the sun and warmth in recent days means less cause for concern.

"When it's dry, you can slack off a bit," Zilnicki said.

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