Washington County has become the 11th Minnesota county suspected of having an infestation of emerald ash borer, the invasive pest that has killed tens of millions of ash trees in two dozen states.

The Minnesota Department of Agriculture said Thursday that an adult emerald ash borer was found on a survey trap at the St. Croix Rest Area on Interstate 94. Tunneling consistent with the invasive pest also was discovered on a nearby tree.

In August, two adult emerald ash borers were found in Chisago County, just north of the Washington County border.

The Washington County specimen was sent to the U.S. Department of Agriculture for confirmation, which is expected later this week.

As a follow up, Washington County could join Anoka, Chisago, Dakota, Fillmore, Hennepin, Houston, Olmsted, Ramsey, Scott, and Winona counties in a state and federal quarantine. The quarantine is designed to limit the movement of anything infested with ash borers, including ash trees and ash tree limbs, and hardwood firewood.

Ash borer larvae kill trees by tunneling into the wood and feeding on the tree’s nutrients. The insect was discovered in Minnesota in 2009.

Kevin Giles