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BOZEMAN - Montana's seed potato industry is under attack by the same disease that caused the Irish potato famine in the 1840s.

The plant disease is showing up on potatoes and tomatoes in the Flathead Valley, and a Montana State University researcher says that if home and commercial growers don't stop the spread, the state could be in trouble.

The first symptoms of the disease are small, dark, circular to irregularly shaped spots commonly occurring first on lower leaves. Although, under epidemic conditions, all leaves may be infected. On a cool damp morning there may be a white, velvety mold growth visible on the underside of these leaf spots or on stem lesions.

Montana State University Barry Jacobsen says light blight is quite uncommon in Montana, but the weather conditions this year have been ideal for the disease.

"You know, the seed potato industry here in Montana is about a $30 million a year business and the buyers of our seed want disease-free seed. And this could be a potential problem," Jacobsen said.

Anyone who finds the disease on tomato plants should remove the plants and throw them away immediately in order to prevent the spores from getting airborne. Jacobsen added that underground potatoes won't be affected as long as you remove the top of the plant.

The source of infection was most likely infected potato seed or tomato transplants brought into the Flathead region from other states. Potato seed and tomato transplants produced in Montana should be free of this disease.

Montana isn't the only state dealing with the problem. An alert was issued by the University of Massachusetts-Amherst in August about Phytophthora infestans after it showed up in tomato plants in the Bay State.

Learn more about the Great Potato Famine of the 1840s by clicking here.