Emerald ash borer (EAB) reached Illinois in 2006 and has now killed tens of millions of ash trees across the Midwest. Every ash tree in the Fox Valley is in its path. If you have one in your yard and you haven't dealt with it, this article is the 10-minute version of what you need to know.
Is the tree you're looking at actually an ash?
Two quick identification checks:
- Opposite branching. Ash branches come off the trunk in pairs, directly across from each other. Walnut, maple, and dogwood also have opposite branching; oaks, elms, and most other trees do not.
- Compound leaves. Each leaf is made up of 5–11 leaflets along a central stem. The whole leaf is the unit that drops in fall.
If you have an alternating branch pattern or a simple (single-blade) leaf, it's not an ash and EAB doesn't apply.
Signs of infestation
- D-shaped exit holes — about 1/8 inch, on the bark. The smoking gun. Hold a coin up to one.
- Canopy dieback starting at the top — EAB-infested ash trees thin out from the top down and from the outside in.
- Epicormic shoots — small sprouts erupting from the trunk and major limbs, especially below the dieback. The tree is trying to compensate.
- S-shaped tunnels under the bark — peel a piece of loose bark and look for the wavy galleries. Definitive.
- Heavy woodpecker activity — woodpeckers eat EAB larvae. If a previously quiet ash has become a woodpecker condo, the larvae are there.
Is the tree worth treating?
Treatment with systemic insecticides (typically trunk injection with emamectin benzoate every 2–3 years) is effective when started early. The hard question: is this tree worth $200–$500 every 2–3 years for the rest of its life?
Our general framework:
- Less than 30% canopy loss + healthy structure → treatment usually pencils out. The tree may live another 20+ years.
- 30–50% canopy loss → judgment call. Often worth treating if it's an important landscape tree (shade, view, mature size).
- More than 50% canopy loss → removal is almost always the better investment.
- Already mostly dead → remove now, before it becomes a hazard. Dead ash trees become brittle fast and are dangerous to remove.
Time is a factor. Dead ash trees are dangerous to climb and difficult to fell in pieces — the wood splinters unpredictably. The same tree, removed while still partially alive, is dramatically cheaper and safer than the same tree removed two years later as a dead snag.
What about the dead ones in the woods?
If you have wooded property and several dead ash standing in it, prioritize the ones within striking distance of structures, driveways, paths, and property lines first. Trees in the deep woods that can fall harmlessly can be left to decompose — they're valuable wildlife habitat. We can walk a property with you and prioritize.
