Farmers are well into the potato harvest, but there’s uncertainty across the country as they await word from the U.S. Department of Agriculture on new regulations to control the “mop-top” virus.

The problem is much greater than initially believed when the virus’ existence in the United States was confirmed for the first time in July at the University of Maine Aroostook Research Farm in Presque Isle.

Canadian officials later disclosed that the virus has been found in more than 100 samples from eight states over an 18-month period.

Scientists from the Canadian Food Inspection Agency and the USDA’s Animal and Plant Health Inspection Service have been scrambling to uncover the extent of the virus and to determine what to do about it.

“If you’re a grower, there’s an air of uncertainty. That’s been difficult,” said John Keeling, executive director of the National Potato Council, which is based in Washington, D.C.

The fact that the virus has been found in states other than Maine may be a blessing in disguise, he said.

Because it has been found in so many places, government regulators may be looking at “management protocols” instead of quarantines for particular regions, states or farms, Keeling said.

But Dennis Corsini, a research plant pathologist at the USDA’s Agriculture Research Service in Aberdeen, Idaho, said it’s too early to say what type of regulations will be adopted.

“We don’t know how it’s going to end up until we have a lot more information,” Corsini said Friday.

The mop-top virus, which is harmless to people, produces rings of discoloration inside the potatoes, making them unmarketable. It can lead to yield reductions of 20 percent, scientists say.

Complicating matters, the soil-borne virus can survive for more than 10 years in contaminated fields.

The virus has caused problems for years in Europe, where it received its name because the tops of infected potatoes resemble a mop-top hairdo. Many U.S. industry officials now believe it probably has been in potato fields in North America for years, unknown to scientists.

The Canadian Food Inspection Agency has imposed restrictions on potatoes from eight states: Florida, Idaho, Maine, Maryland, North Carolina, Oregon, Virginia and Washington. California was initially on the list but was removed.