Emerald Ash Borer

The emerald ash borer is an exotic pest, native to Asia, currently threatening ash trees (including white, green and black ash) in the Great Lakes region. The emerald ash borer belongs to a group of insects known as metallic wood-boring beetles. Since its discovery in southeastern Michigan during 2002, it has spread to a total of 13 states and 2 Canadian provinces. In 2008 Emerald Ash Borer was confirmed in Wisconsin. Since then, four other Emerald Ash Borer discoveries have been made in Wisconsin. To date, there are no confirmed sightings on the CNNF.

Transmission of this pest is accelerated by the inadvertent transportation of larvae in logs, firewood and nursery stock.

Ash trees are quite abundant in Wisconsin, with estimates as high as 717 million trees total, and are commonly found in both urban and forest settings. Ash is a component of three forest types in Wisconsin, including: 1) Elm/Ash/ Cottonwood; 2) Northern Hardwood; and 3) Oak/Hickory. An ash tree is most easily identified by its opposite branching pattern (two branches come off the main stem, one on each side and opposite each other) and compound leaves with 5-11 leaflets. Leaflets are moderately toothed and may be stalked or sessile.

If you come across a potential infestation or have questions, please contact: Mark Theisen, Chequamegon-Nicolet National Forest Silviculturalist, at 715-362-1346.

For more information on the emerald ash borer, you may call or visit your local Forest Service office or visit the Forest Service emerald ash borer website. Thank you for your help.

adult emerald ash boreradult emerald ash borer
The adult emerald ash borer, pictured in diagrams A and B, is bright metallic green in color, about 1/2 inch long and 1/16 inch wide.

larva emerald ash borer

Emerald ash borer larva shown in diagram C, typically leave D-shaped exit holes on the branches and trunk of the ash trees.

ash tree leaf
An ash tree leaf is pictured in diagram D. Identification may be difficult during leaf-off season. Black ash trees lose their leaves very early in the fall.