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Maine ‘Ground Zero’ for New Potato Disease

Evidence of the potato bacteria known as Dickeya dianthicola

A bacteria affecting Maine seed potatoes could pose big problems for Aroostook County farmers who sell to growers on the Eastern Seaboard.

Scientists at the Maine Department of Agriculture are consulting with European researchers who have a longer history with the bacteria known as Dickeya dianthicola. The bacteria creates dark lesions on the plant’s stems that farmers associate with a potato disease commonly known as blackleg.

Normally, blackleg leads to rotting of potatoes. Now, Dickeya dianthicola — that has many symptoms commonly associated with blackleg — poses another threat to farmers in Aroostook County, where 90 percent of Maine’s $750 million annual potato crop is grown.

Tim Hobbs, director of grower relations at the Maine Potato Board in Presque Isle, says the problem first surfaced when farmers who sell seed potatoes to out-of-state growers begin hearing complaints.

“It was about the time that we started planting here towards the end of May last year that we started getting calls from the mid-Atlantic states saying that we’ve got a blackleg problem,” Hobbs says.

Some of the growers in Pennsylvania and Maryland who buy large amounts of seed potato from Maine farmers wound up losing up to half of the crops they had planted. The seed potatoes, Hobbs says, appeared fine when they left Maine. Still, the mid-Atlantic state growers were convinced they were seeing the symptoms of blackleg, Hobbs says Maine horticulturists went to work on the problem.

“In the middle of June we hear this word Dickeya and we’re saying what the heck is Dickeya and where’d it come from, so we as an industry and the individual growers need to be able to provide their customers with some assurance of what’s going on, and so there’s a clamor because this wasn’t a pathogen that had had a lot of work done on it in the U.S.” Hobbs said.

While research into the origins of Dickeya and how it might best be controlled have been ongoing in England and Europe for 25 years, it’s new to the United States and, with its arrival, Maine has gained a rather dubious distinction.

“Unfortunately Maine is ground zero for this disease right now,” said Ann Gibbs, division director for the Maine Department of Agriculture’s animal and plant health division.

Gibbs is working with the state’s potato industry to create new forms of testing to identify the presence of the bacteria and to bolster confidence in the quality of the seed potatoes shipped from Maine. She says a lot of progress has been made over the last year. For example, it’s now clear that the bacteria only develop during certain conditions when humid weather allows.

In an effort to further increase buyer confidence Gibbs says a new rule regulating the seed certification program is in the process of being finalized.

“The proposed rule did have a specific tolerance for blackleg, a seed lot would have to meet certain tolerances for blackleg specifically in order to be considered certified seed,” Gibbs says. “And if it didn’t meet that tolerance, it was kicked out. Those should be in place for this coming season.”

In the meantime, Hobbs and other industry leaders at the Maine Potato Board will have to wait until later this year to determine the effect that Dickeya is having on Maine’s seed potato industry.