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Silver scurf, caused by a fungus, is a common potato disease and found in all major production areas of the U.S., including the Red River Valley of western Minnesota and northeast North Dakota.(Photo by Andrew Robinson)

Silver scurf: Great name, but bad for spuds

GRAND FORKS, N.D. — Fans of colorful, alliterative language may like "silver scurf." Not Red River Valley potato growers; they see the crop disease as a growing threat.

"I'm getting more questions about it at harvest," said Andy Robinson, Fargo, N.D.-based potato extension agronomist for both North Dakota State University and the University of Minnesota.

He helped to organize potato educational sessions during the recent International Crop Expo in Grand Forks, N.D., and brought in Amanda Gevens to speak on the crop disease on Feb. 22.

Gevens, a professor in the plant pathology department at the University of Wisconsin, also is seeing more cases of silver scurf. She described the disease "as gray, silver and shiny patches" that are "more obvious on red and purples," but seen on yellow and russet potatoes, too.

Silver scurf, caused by a fungus, is a common potato disease and found in all major production areas of the United States, including the Red River Valley of western Minnesota and northeast North Dakota.

The disease, specific to potato tubers, causes blemishes on spuds. Though the effect is mostly cosmetic, some potatoes affected by the disease have been rejected by industry buyers.

Efforts to combat silver scurf are complicated by its close resemblance to black dot, another crop disease. Even Gevens can have trouble distinguishing the two diseases on affected potatoes.

"Whodunnit? Is it a silver scurf problem? Or is it a black dot problem," she said. "It's hard to tell these apart. Sometimes you can't tell them apart."

One important difference: silver scurf is tied to infected seed, while black dot is more of a soil/field debris issue, Gevens said.

No commercial cultivars resistant to silver scurf are available yet, though work to develop them is underway.

Use of uninfected seed, which can be hard to get, helps to control the disease, as does early harvest and chemical use,

Storage conditions also influence the extent of silver scurf in affected potatoes.

"High humidity in storage encourages it," Gevens said.

Research also shows that smaller storage volumes help to control core temperatures and hold down silver scurf. But limiting storage volumes may not always be feasible, she said.

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