The United States closed its borders to shipments of Prince Edward Island potatoes Tuesday, citing concern about a fungal disease called Potato Wart.

There was no immediate indication of how long the closure would last but it comes at a bad time. P.E.I. farmers are now harvesting their crop, and normally about 8% of it is sold to U.S. markets.

The outbreak of Potato Wart was found in a field in Lower New Annan last week. It was the first time it had ever been seen in P.E.I.

The disease poses no threat to humans but produces growths on the potatoes that makes them unmarketable.

When news of the outbreak reached the U.S., authorities there dispatched a team of inspectors to P.E.I. and it was on the basis of their report that the border was closed.

"We had first gotten reports early last week, and they went and inspected. And this is a result of those inspections and testing samples," said Maine Congressman John Baldacci.

Maine and Prince Edward Island are fierce competitors in the potato business, but Baldacci said there were no politics involved in the border closure.

"We've been doing an awful lot more with Canadian processors and Canadian agriculture and we would like to develop more of those ties across the border so that we can work together as we compete with Idaho and California and others. This is something we take very seriously in agriculture, to contain this and eradicate this," he said.

"They've coined it as a temporary emergency action to protect their industry," said Don Love of the Canadian Food Inspection Agency.

"It is a quarantinable pest. We have an obligation to demonstrate that it is isolated and it is a very small issue. I think to date that we have demonstrated in that direction, but when we get some more information, when we get some hard data, I think that it will go a long way to resolve this issue," he added.

Love said Canadian investigators are now trying to determine the source of the Potato Wart, and how widespread the infestation is.

"It's a fungus that occurs in the soil. It could have been there for a considerable period of time or it could have been introduced recently. We haven't got enough information yet to really clearly identify why it's here," he said.

Love advised farmers and shippers to be patient while the investigations are being carried out.

"We're optimistic, and we hope that we can get this resolved very quickly," he said.