Wisconsin officials have confirmed emerald ash borer in the northern unit of Kettle Moraine State Forest.
Department of Natural Resources staff found an adult beetle in a trap set at the Mauthe Lake campground.
Officials say the pest poses a minimal threat on most of the 30,000-acre northern unit, because it contains few ash trees.
It's the first time the tree-killing pest has been found in Fond du Lac County. But the county has been under quarantine for emerald ash borer since 2008, because it's near infestations in neighboring Washington County.
Wisconsin agriculture officials say emerald ash borer also was found in Watertown's Riverside Park. Dodge County will be put under quarantine.
The quarantine prohibits wood products from being moved out of the county to areas that are not infested.