Invasive Insect Threatens Minnesota’s Ash Forests

The Emerald Ash Borer (EAB), an invasive insect native to Asia, has spread to 36 U.S. states and parts of Canada since its arrival in Minnesota around 1990. It now threatens forests as far north as Cass County and is expected to reach Beltrami County soon. With an estimated 1 billion ash trees in Minnesota — many vital to wetland ecosystems — the death of these trees from EAB could significantly alter forest habitats and harm native plant and animal species. The spread has been aided by mild winters, which are no longer killing off EAB larvae as harsher cold once did.

Ash trees have long been planted in cities to replace elms lost to Dutch Elm disease and birches lost to bronze birch borer, but the rise of EAB has pushed cities to rethink this strategy. Municipalities are now diversifying tree plantings to reduce the risk of future widespread loss. Homeowners with healthy ash trees are advised to start planting replacement trees such as maple, birch, or basswood this spring to ensure continued canopy coverage. Additionally, residents should avoid moving ash firewood from infested areas, as it can spread the pest to new locations.

Early signs of EAB infestation include thinning tree canopies, bark splitting, D-shaped exit holes, and increased woodpecker activity. Once detected, management options like insecticide treatments can slow the damage. Resources from the University of Minnesota Extension provide guidance on identification and treatment. While managing EAB across large landscapes requires coordination among agencies and landowners, individuals can still make a meaningful impact by taking preventive steps and planting a variety of tree species to support long-term forest health.