Emerald Ash Borer in Wisconsin: 2026 Update and Treatment Options

Emerald Ash Borer in Wisconsin: Where Things Stand in 2026

The emerald ash borer (EAB) has now been confirmed in every Wisconsin county. Since the first detection in Ozaukee County in 2008, this invasive beetle has killed millions of ash trees across the state. Wisconsin homeowners, municipalities, and arborists continue to face difficult decisions about whether to treat or remove their ash trees.

EAB larvae feed beneath the bark, severing the nutrient pathways that keep ash trees alive. Without intervention, an infested ash tree typically dies within two to four years. The economic toll across the Midwest — including Wisconsin, Illinois, Indiana, Michigan, Minnesota, Iowa, Ohio, and Missouri — is measured in billions of dollars.

Current Spread Across Wisconsin Counties

As of early 2026, the heaviest mortality is concentrated in southeastern Wisconsin, including Dane, Milwaukee, Waukesha, and Racine counties, where EAB has been established the longest. Northern counties such as Marathon, Lincoln, and Oneida are now seeing significant canopy loss as second-wave infestations mature. Counties along the Mississippi River corridor show increasing activity from cross-border spread with Minnesota and Iowa.

The Wisconsin DNR estimates that the state had approximately 770 million ash trees before EAB arrived. Current projections suggest that 99% of untreated ash trees in infested areas will eventually be killed.

EAB Treatment Options for Wisconsin Homeowners

If your ash tree is still relatively healthy — meaning it retains at least 50% of its original canopy — treatment may be a viable option. Here are the primary approaches used in Wisconsin and across the Midwest:

• Trunk injection with emamectin benzoate (TREE-age) is the gold standard. A certified arborist drills small ports into the trunk flare and injects the insecticide directly into the vascular system. Protection lasts two to three years per treatment.
• Soil drench with imidacloprid is a less expensive option suitable for smaller ash trees (under 20 inches DBH). Homeowners can apply this themselves, but uptake takes several weeks and efficacy is lower than trunk injection.
• Bark spray with bifenthrin provides seasonal protection for the trunk and main branches. This requires annual reapplication and is best used as a supplemental measure.

Treatment is most effective when started before EAB is detected in your tree. Preventive treatment should begin when confirmed infestations are within 15 miles of your property.

When to Remove Instead of Treat

Removal is the better choice when:

• The tree has lost more than 50% of its canopy
• The trunk shows extensive bark splitting and woodpecker damage
• Multiple D-shaped exit holes are visible (indicating heavy adult emergence)
• The tree has structural defects that make it a hazard
• Budget constraints prevent ongoing biennial treatments for the life of the tree

Ash wood becomes brittle quickly once the tree dies. Dead ash trees are significantly more dangerous to remove than living ones because branches snap unpredictably during the removal process. Do not delay removal once a decision is made.

Cost Estimates for EAB Treatment in Wisconsin

Costs vary by tree size and treatment method:

• Trunk injection (emamectin benzoate): $150 to $400 per treatment depending on tree diameter, repeated every two years
• Soil drench (imidacloprid): $30 to $100 per year for DIY application; $75 to $200 if professionally applied
• Tree removal: $500 to $3,000+ depending on tree size, location, and accessibility
• Stump grinding: $100 to $400 additional

Over a 10-year period, treating a medium-sized ash tree costs roughly $750 to $2,000, while removal and replacement typically costs $1,500 to $4,500. For many Wisconsin homeowners, treatment is the more economical choice for healthy, well-placed trees.

Frequently Asked Questions

How do I know if my ash tree has EAB?

Look for D-shaped exit holes (about 1/8 inch wide) on the bark, S-shaped larval galleries beneath the bark, canopy thinning that starts at the top of the tree, increased woodpecker activity, and epicormic sprouting (new shoots growing from the trunk). If you see these signs, use our tree diagnosis tool or contact a certified arborist for confirmation.

Is it too late to save my ash tree?

If the tree retains at least 50% of its canopy and has no major structural defects, treatment with emamectin benzoate trunk injections can still protect it. Trees that have lost more than half their canopy are generally too far gone to recover, even with treatment. An ISA Certified Arborist can assess your specific tree.

How much does EAB treatment cost in Wisconsin?

Professional trunk injection with emamectin benzoate typically costs $150 to $400 per treatment depending on the diameter of your tree. Treatments are repeated every two years. For a typical 20-inch diameter ash tree in Wisconsin, budget approximately $200 to $300 per treatment cycle.

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If you have ash trees on your property in Wisconsin or anywhere in the Midwest, take action now. Use the TreeIssues directory to find an ISA Certified Arborist in your area for a professional assessment.