The emerald ash borer is an invasive wood-boring beetle from Asia, first detected in Michigan in 2002. It has since killed hundreds of millions of ash trees and is now established across most of the eastern United States, including Illinois, Wisconsin, Minnesota, and Maryland. If you have ash trees on or near your property, this pest matters, even though the solution lies with a certified arborist, not a standard pest control operator.
Identification
Adult beetles are about a third to a half inch long, slender, and iridescent bright green. The abdomen beneath the wing covers is a purplish or coppery magenta, visible when the wings are spread. Adults are present from late May through August and are active during warm, sunny days, but they are small enough and high enough in the canopy to go unnoticed.
The more practical identification happens on the tree. Look for the D-shaped exit holes the adults chew when they emerge, about one-eighth of an inch wide. These are distinctive and diagnostic. Under the bark of infested trees, larvae create winding, S-shaped feeding galleries in the cambium and phloem, the living tissue just beneath the bark. Woodpecker damage in winter is another strong indicator: woodpeckers excavate actively for EAB larvae and leave a flecked, blonded appearance on the bark.
To identify ash trees themselves, look for opposite compound leaves with five to nine leaflets, diamond-patterned bark on mature trees, and paired winged seeds in fall. No other common native tree has this combination.
Behavior and Habitat
The life cycle takes one to two years and occurs almost entirely inside ash tree tissue. Adults emerge in late spring, feed briefly on ash leaves, then mate. Females lay eggs in bark crevices. Larvae hatch and bore immediately into the cambium, feed through fall, overwinter under the bark, pupate the following spring, and the cycle repeats.
This larval feeding girdles the tree from the inside. An ash can go from fully leafed out to dead within two to four years of initial infestation. An infested tree becomes a source population that spreads the beetle to nearby ash trees, which is why a single infested tree in a neighborhood affects the broader local ash population.
Signs of an Infestation
Early infestation is hard to detect because the larvae are under the bark before any external symptoms appear. By the time you see crown dieback, the infestation is already well established. Key signs include: canopy thinning starting at the top; D-shaped exit holes on the trunk and larger limbs about the diameter of a pencil eraser; vertical bark splits; increased woodpecker activity with pale bark flecking in winter; and prolific sprouting from the base of the trunk. If you see any combination of these on an ash, contact a certified arborist.
Health and Property Risks
Emerald ash borer does not affect human health directly. The concern for homeowners is what a dead ash tree means for the property. Ash trees killed by EAB become structurally hazardous within a few years of death. The wood is notably brittle once dead, and large limbs fail and drop unpredictably. A dead ash near a home, garage, or area where people spend time is a significant safety and liability risk, and removal becomes urgent once the tree is past a certain point of decline.
Dead ash trees also attract secondary pests. Carpenter ants readily colonize soft dead wood, and a large dying ash adjacent to the house is a common source of carpenter ant pressure in the structure. Do not transport ash firewood. This is not just a suggestion. Moving potentially infested ash wood is restricted under state and federal quarantine regulations.
Treatment Options
Treating emerald ash borer requires a licensed applicator or certified arborist. It is not standard pest control work.
Systemic insecticide injection is the primary method for trees worth saving. Emamectin benzoate (TREE-age) is injected directly into the trunk and provides two years of protection per treatment. Imidacloprid can be injected or applied as a soil drench but requires annual application. Both require professional equipment and licensing.
Treatment is cost-effective for healthy trees with significant value that have not yet passed 50 percent canopy dieback. Trees with more advanced decline are better candidates for removal. Untreated ash in infested areas will almost certainly die. If you have multiple ash trees, an arborist can help triage which to treat and which to remove while the wood is still sound.
Prevention
Ash trees can be treated prophylactically if EAB is confirmed in the county. A preventive injection on a healthy ash puts you ahead of the problem. Once symptoms appear, you are managing the decline, not preventing it.
Do not move ash firewood. Emerald ash borer spreads primarily through infested firewood and nursery stock, and every affected state has quarantine regulations restricting wood movement. Report trees showing infestation signs to your state department of agriculture or local extension service.
What It Costs
Systemic injection treatment by a certified arborist runs roughly $8 to $12 per inch of trunk diameter, measured at chest height. A 14-inch ash costs approximately $120 to $170 per treatment, with emamectin benzoate treatments repeating every two years. Imidacloprid soil drenches are less expensive per application but require annual treatment. Removal of a dead or dying ash tree ranges from $500 to $2,500 or more depending on size, location, and the complexity of the job. A large ash near a house or over a utility line is a difficult removal and costs significantly more than a tree in an open yard. Emergency removal of a structurally failed tree is the most expensive scenario. Acting while the tree is still alive and the wood is sound keeps removal costs lower.
When to Call a Professional
If you have ash trees on your property and you have not had them assessed, call a certified arborist now, particularly if EAB is known to be present in your county. Do not wait until you see significant crown dieback, because by that point the window for effective treatment may have closed. An arborist can tell you whether your trees are infested, how advanced the damage is, and whether treatment or removal is the better path.
For secondary pest concerns, such as carpenter ants in a declining ash tree near the house or an influx of bark beetles in dead wood, a standard pest control operator is the right call. But the tree itself needs a certified arborist, not an exterminator.