If you have ash trees on your property in the Chicago area, you have likely already heard of the Emerald Ash Borer. What you may not fully appreciate is the speed at which this invasive beetle can kill an otherwise healthy tree — and how treatable it is when caught in time.
The Emerald Ash Borer (Agrilus planipennis) is a metallic green beetle native to Asia that arrived in the United States around 2002. It has since killed hundreds of millions of ash trees across 35+ states. In Northern Illinois, it has effectively transformed the urban canopy, wiping out vast numbers of ash trees that once shaded streets, parks, and residential properties.
How EAB Kills Trees
The damage is done by larvae, not the adult beetles. Adult beetles emerge in late spring and early summer, feeding on ash foliage and laying eggs in bark crevices. When eggs hatch, the larvae bore through the bark and feed in the cambium — the layer just beneath the bark responsible for transporting water and nutrients between roots and canopy.
As larvae create their distinctive S-shaped feeding galleries, they disrupt the tree's vascular system. A heavily infested tree can't move enough water and nutrients to survive. Most untreated ash trees die within 3 to 5 years of initial infestation — sometimes faster.
Signs of EAB Infestation
- Canopy dieback — thinning or dying branches starting at the top of the tree
- Epicormic sprouting — new growth shooting from the trunk below the dying crown
- S-shaped galleries — visible under peeling bark sections
- Woodpecker activity — birds excavating bark to feed on larvae
- D-shaped exit holes — small, flat-sided holes in the bark where adults have emerged
- Bark splitting — vertical cracks as the tree attempts to compartmentalize the damage
Important: Not every ash tree showing stress is infested with EAB. Other insects, drought stress, and disease can cause similar symptoms. A proper diagnosis from an ISA-certified arborist ensures you're treating the right problem.
Treatment Options That Work
The good news: EAB is very treatable, and treated trees can survive and thrive for decades. The key is starting treatment before the tree reaches roughly 50% canopy decline. Beyond that threshold, the tree's vascular system is too compromised to move the treatment effectively.
Trunk Injection
The most widely used and effective treatment method. An insecticide — typically emamectin benzoate — is injected directly into the tree's vascular system through small holes drilled in the base of the trunk. The tree distributes the insecticide upward through its xylem, killing larvae throughout the crown. A single treatment lasts 2 to 3 years.
Soil Drench / Basal Bark Spray
Imidacloprid can be applied as a soil drench or basal bark spray. The tree uptakes the systemic insecticide through its roots. This method works well for preventive treatment or lighter infestations, and is easier to apply. It is generally less effective for severe infestations than trunk injection.
Is Your Ash Tree Worth Treating?
The question we get most often: is this tree worth treating, or should I just remove it? Our answer depends on several factors — tree health, size, location, structural condition, and the homeowner's goals. A large, otherwise healthy ash in a prominent location is almost always worth treating. A tree already showing 50%+ decline may be too far gone.
What we've seen repeatedly is that homeowners who act early — before obvious symptoms appear, or at the first signs of canopy thinning — get excellent results. Richard J. in St. Charles is a good example: "All the Ash trees in my neighborhood have died except mine. My Ash trees are beautiful, healthy." That outcome comes from early treatment and ongoing monitoring.
If you're not sure whether your ash trees are at risk or showing early signs of EAB, the right move is a professional evaluation. Contact Emerald Tree Care to schedule an assessment — we serve Schaumburg, Roselle, Barrington, Palatine, and throughout Western Chicagoland.
