The department has banned additional shipments into the U.S. and plans to search for the golden potato cyst nematode in fields in Idaho, Oregon, Washington, California, North Dakota, Colorado, Maine and Nebraska.
U.S. officials are concerned that discovery of the golden nematode in any of the eight states could lead to some countries banning U.S. potatoes, which happened in 2006 with the discovery of the similar pale potato cyst nematode in Idaho.
The department closed the U.S. border to seed potatoes from the Canadian province of Alberta on Nov. 1 after officials with the Canadian Food Inspection Agency on Oct. 23 announced the discovery of the golden nematode at two farms about 60 miles apart.
"At this point the concern we have is whether or not Canada has been able to determine what the extent of the infestation is in Canada," said Larry Hawkins, a spokesman for the agriculture department.
Earlier this month, Mexico also cut off shipments of Alberta seed potatoes. Canadian seed growers have since mounted a campaign to reopen the U.S. border.
Hawkins said not knowing the extent of the problem in Alberta makes it more difficult for U.S. officials to determine what problems they face. He also said finding where all the seed potatoes from Alberta have been planted in the U.S. might be impossible.
"We'd like to be able to trace any potential seed shipments from Alberta all the way to the field where they might have been planted," Hawkins said. "However, I don't know that we'll be able to do that. I'm not certain that the shipments are identity preserved all the way to a field."
The nematodes feed at the roots of potato plants and can reduce crop production by 80 percent. Officials say the pest is not harmful to humans and doesn't have any effect on the potatoes themselves.
Seed potatoes - a small potato or a larger potato cut into pieces - are an inch or two in diameter and are often grown in colder areas at higher elevations. When planted, they grow into potato plants that produce more potatoes.
Idaho is still dealing with the discovery in 2006 of the pale potato cyst nematode, which initially led Canada and Mexico to ban all fresh potato imports from Idaho, and Japan to ban all fresh U.S. potato imports.
Earlier this year, Canada and Mexico lifted their bans. Japan still bans fresh potatoes from Idaho, but accepts them from other U.S. states.
Idaho grows about one-third of all the potatoes in the United States, and this year produced 13.2 billion pounds. This year's crop is still being marketed, but last year's slightly smaller crop was worth $712 million to Idaho farmers.
The state imports about 5 percent of its seed potatoes in all varieties from Alberta, and Cooper predicted possible shortages of red and yellow potatoes as a result of the ban.
Washington imports about 30 percent of its seed potatoes from Alberta, said Brad White, pest program manager for the Washington State Department of Agriculture. He predicted some growers will face seed potato shortages.
"Once the federal side determines the sales of potentially infested seed potatoes, then we'll have an idea of how big our exposure is," White said.
Oregon imports up to 13 percent of its seed potatoes from Alberta, said Jim Cramer of the Oregon Department of Agriculture. He said state authorities will be working with federal officials to find fields planted with seed potatoes from Alberta.
He said Oregon growers will likely face seed potato shortages.
"Some of them are scrambling for seed," he said. "But the U.S. can't in good conscience open up the seed potato border."
By Keith Ridler