Agricultural officials have found potato cyst nematode in a field adjacent to two others in Idaho that are already infected, bringing to eight the number of fields that have been infested since 2006.

The initial discovery closed some foreign markets to U.S. potato growers. An extensive testing protocol allayed fears of importers. The most recent finding isn't expected to affect trade.

About 1,100 acres of infested fields are in Bingham, Bonneville and Jefferson counties in southeast Idaho.

The latest finding in a 145-acre field was confirmed by DNA testing conducted by the U.S. Department of Agriculture in Beltsville, Md.

The most recently infested field is associated with the previous findings either through the same owner, the same machinery being used or the same seed source.

After the nematodes were first discovered in 2006, Japan banned all fresh U.S. potato imports, and Canada and Mexico banned all fresh potato imports from Idaho.

Earlier this year, Canada and Mexico lifted their bans. Japan still bans fresh potatoes from Idaho, but accepts them from other U.S. states.

Potato cyst nematodes feed on plant roots and can reduce production by up to 80 percent.

To subscribe to the print version of The Grower, click here.