The recent discovery of an emerald ash borer in Washington County has raised concern that the beetle could spread quickly and endanger groves of ash trees in parks and cities.

After reviewing the problem Tuesday, county commissioners said they wanted an aggressive plan — involving municipalities — to deal with the likelihood that the invasive pest will appear in great numbers.

“This one is going to be huge. Trees don’t have boundaries,” said Mike Polehna, a Stillwater City Council member and retired county parks manager.

The ash borer threat, Polehna told commissioners, would rival Dutch elm disease, which decades ago killed tens of thousands of trees in Washington County and elsewhere in the metro area.

In early October, Washington County became the 11th Minnesota county to find evidence of an emerald ash borer, the invasive insect that has laid ruin to ash trees in two dozen states. An adult ash borer was found on a survey trap at the St. Croix rest area on Interstate 94.

Commissioners said Tuesday that they want a “proactive” strategy that would include public forums and partnerships with the Minnesota Department of Agriculture and the county’s cities.

Gary Kriesel, who chairs the board, said he wanted a strong Washington County role in preventing the spread of the ash borer westward from the metro area into portions of Minnesota where infestations haven’t been found.

“We have an obligation,” he said. “The damage is done here. What do we do to stop it from progressing?”

Ash borer larvae tunnel into trees and feed on its nutrients. The insect was discovered in Minnesota in 2009.

The Washington County discovery comes after similar infestations in Anoka, Chisago, Dakota, Fillmore, Hennepin, Houston, Olmsted, Ramsey, Scott and Winona counties. State and federal quarantines limit the movement of anything infested with ash borers, including ash trees and hardwood firewood.

The county’s natural resources coordinator, Dan McSwain, said in his Tuesday presentation to commissioners that there’s no evidence of infestation in county parks — some of which have large numbers of ash trees planted before the practice was discontinued in 2006.

“You don’t just want to sit and let it go or you’ll be in trouble,” said Mark Abrahamson, who supervises the pest detection unit at the Minnesota Department of Agriculture. “We’re getting to the point in the metropolitan area that more ash trees are being attacked more quickly.”

Polehna, who participated in ash tree inventories when he worked for the county, told commissioners that a task force should be assembled soon.

“You don’t know it’s there until it’s too late,” he said after the board meeting. “It lives under the bark and once it starts spreading you don’t know it’s there until your tree starts dying.”