Can an ash tree be saved from emerald ash borer?

A healthy, high-value ash can often be protected with preventive trunk-injection treatments applied by a licensed pesticide applicator, but the treatments are systemic and recurring — usually repeated every couple of years for the life of the tree. Once a tree has already lost a large share of its canopy, treatment is rarely worth it, and removal becomes the safer choice.

How do I know if I have an ash tree?

Ash trees have branches and leaves arranged directly opposite each other, compound leaves made of five to nine leaflets on a single stem, and mature bark with a tight diamond or ridge pattern. If you're unsure, an arborist can confirm the species during a visit — it's worth knowing, because ash is one of the few common Denver-area trees at direct risk from this pest.

Why can't I just wait and see with a dead ash tree?

Ash killed by emerald ash borer becomes brittle unusually fast. Branches and whole trunks can fail with little warning, which makes a standing dead ash both a hazard and a harder, more expensive tree to remove safely. Acting while the wood still has some integrity is safer for everyone.

Is it safe to move firewood from an infested ash tree?

No. Moving ash firewood is one of the main ways emerald ash borer spreads to new areas. Keep any wood on-site or dispose of it locally, and don't haul it to a cabin, campsite, or another property.

Tree Services

Emerald Ash Borer in Colorado: What Denver-Area Homeowners Need to Know

By the Stroikos Services team · July 9, 2026 · Serving the Denver South Metro area

If you own a home in the Denver South Metro area, there’s a good chance at least one tree in your yard or on your street is an ash — and ash trees across the Front Range face a serious, spreading threat. The emerald ash borer, a small metallic-green beetle, kills ash trees that aren’t protected, and it has been confirmed in Colorado since 2013, when it first turned up in Boulder. Since then it has been found in a growing list of Front Range communities. Here’s what that means for you as a homeowner, and what you can do about it.

Why ash trees matter here

When neighborhoods across the metro area were built out, ash was planted heavily because it grows fast, tolerates our conditions, and shades a yard quickly. That popularity is now the problem: ash makes up a large share of the regional urban canopy, and this pest attacks ash specifically. A single infested, untreated ash usually dies within a few years, so a street lined with ash can lose a lot of shade — and value — in a short window.

How to tell if you have an ash tree

Before you worry about the borer, confirm the species. Ash trees share three tells:

Opposite branching. Branches, buds, and leaves grow directly across from each other in matched pairs, not staggered along the stem. Few large landscape trees do this, so it’s a strong clue.
Compound leaves. What looks like one leaf is actually a group of five to nine leaflets attached to a single central stem.
Diamond-patterned bark. On a mature trunk, the bark forms tight, interlacing ridges in a diamond-like pattern.

If two of the three line up, treat it as a likely ash and keep a closer eye on it. An arborist can confirm during a visit.

Signs of an infestation

The borer does its damage as a larva tunneling just beneath the bark, where it feeds on the living tissue the tree uses to move water and food between roots and canopy. That’s why symptoms show up in the crown first. Watch for:

Thinning in the upper canopy — the top of the tree looks sparse or bare while lower limbs still leaf out.
D-shaped exit holes — tiny, distinctly D-shaped holes where adult beetles emerged.
S-shaped galleries — winding, S-curved tunnels packed with fine sawdust-like frass under loose bark.
Woodpecker flecking — patches where woodpeckers have stripped bark chasing the larvae, giving the trunk a blond, flecked look.
Epicormic sprouts — sudden shoots of new growth low on the trunk or roots, a stress response.
Bark splits — vertical cracks in the bark, sometimes revealing galleries underneath.

Because these insects can be identified by the work they leave behind, an experienced arborist can often confirm an infestation even without spotting a live beetle. Stressed trees are also more vulnerable, so a drought-weakened ash deserves extra attention.

Your two real options: treat or remove

For any at-risk ash, it comes down to a decision.

Preventive treatment. A healthy, structurally sound, high-value ash can be protected with systemic trunk-injection insecticides applied by a licensed pesticide applicator. The product moves inside the tree to reach the feeding larvae. This is a recurring commitment — typically repeated on a cycle for as long as you want to keep the tree — and it works best as prevention, started before heavy damage occurs rather than as a rescue.

Removal and replacement. If an ash is already in decline, in a risky spot, or simply not worth an indefinite treatment budget, removing it and replanting is the sound long-term move. The strong recommendation is to replace with a diversity of species rather than another single dominant type — a mixed canopy is far more resilient to the next pest that comes along.

There’s no universally right answer; it depends on the tree’s health, its value to your property, and your budget.

When to call a professional

Call an arborist if you have an ash and you’ve spotted any canopy thinning, exit holes, or bark splitting — early confirmation gives you the most options. You should also get professional help deciding between treatment and removal, since trunk injections must be done by a licensed applicator and species identification isn’t always obvious.

Most important: don’t let a dead ash stand. Ash killed by this borer turns brittle fast, and limbs or trunks can fail suddenly, making the tree dangerous to be near and harder to take down safely the longer you wait. And whatever you do, don’t move the firewood — hauling ash wood is a primary way the pest reaches new neighborhoods.

Stroikos Services provides ash evaluations, removals, and replanting guidance across the Denver South Metro. If you’re unsure about a tree, our tree services team can take a look and give you honest options.