HACKENSACK, N.J. — A fungus that caused the infamous 1840s Irish potato famine has hit this summer's commercial and homegrown tomato crop in 13 states, putting farmers and agricultural experts on edge.

"It's a big threat," said Andy Wyenandt, an assistant extension specialist at Rutgers University. "This could have a real impact on commercial growers."

The fungus, phytophthora infestans, causes a late blight that quickly kills affected plants. Its spores can spread easily on the wind from one homeowner's garden to the next and on to commercial fields. This summer's outbreak has been found in plants from Maine to South Carolina.

Many are worried about what this will do to commercial tomato crops, a $21 million industry in New Jersey alone. The blight has also hit potato crops in New York, Pennsylvania and other states.

"This is one of those diseases that, when you mention it to commercial growers, they get nervous," Wyenandt said.

The fungus wiped out all 100 tomato plants in Fred Behnke's back yard in Paramus, N.J., recently.

"The leaves curled up and turned black and each tomato got brown spots and looked rotten," he said. "In two days, it went through the whole garden."

Behnke, a former farmer who is 90, said he had never seen anything like it. He got the plants from a farmer friend in Lancaster, Pa., another area with confirmed cases. Behnke had to pull all the plants out when the blight hit just before July 4. He put them in a plastic bag to kill the fungus and prevent its spread.

The fungus isn't unusual to tomatoes in the Northeast, but it showed up early and is far more widespread this summer. Wyenandt said it's prevalent because an Alabama wholesaler distributed tomato seedlings infected with the fungus to big-box retailers.

The fungus was present on plants supplied to Walmart, Kmart, Home Depot and Lowe's by Bonnie Plants, an Alabama-based wholesaler with 62 growing stations nationwide, Wyenandt said.

Bonnie Plants, the nation's largest tomato plant producer, recently pulled all of its remaining tomato seedlings off retailers' shelves in 12 states, including Pennsylvania, said Ellis Ingram, the company's customer relations manager. The move will cost the company up to $2 million, he said.

"We're very conscientious. We didn't want commercial producers to be affected," Ingram said.