Emerald Ash Borer: Signs and What to Do in Colorado

Emerald ash borer is an invasive beetle that kills ash trees by tunneling under the bark. Common signs include a thinning canopy from the top down, small D-shaped exit holes, S-shaped tunnels under loose bark, shoots sprouting from the trunk, and heavy woodpecker damage. Lightly infested ash trees can sometimes be protected, but heavily damaged or dead ash should be removed before it turns brittle and drops limbs.

Ash trees are some of the most common shade trees in Colorado neighborhoods, and emerald ash borer is now spreading through them. If you have an ash in your yard, here’s how to recognize the beetle, check your tree, and decide what to do next.

What Is Emerald Ash Borer?

Emerald ash borer (often called EAB) is a small, metallic green beetle about half an inch long. It’s native to Asia and was first found in the United States in 2002. Since then, it has killed hundreds of millions of ash trees across the country.

The adult beetles do little harm. The damage comes from the larvae, which hatch on the bark and tunnel just underneath it. Those tunnels cut off the tree’s ability to move water and nutrients. Once enough of the tree is damaged, it starves from the inside out.

Emerald Ash Borer in Colorado

Emerald ash borer was first confirmed in Colorado in 2013 and has since been found in many Front Range communities, including large parts of the Denver metro area. Because ash was planted so widely along streets and in backyards, many neighborhoods have dozens of ash trees within a few blocks.

The beetle spreads slowly on its own, but much faster when infested ash logs and branches are moved to new areas. That’s why infested wood should always be handled and disposed of properly.

Is It an Ash Tree? How to Tell

Emerald ash borer only attacks true ash trees. Before you worry, make sure your tree is an ash:

• Opposite branching: branches and buds grow directly across from each other, not staggered.
• Compound leaves: each leaf is made of 5 to 9 smaller leaflets.
• Diamond-patterned bark: mature ash has tight, crisscrossing ridges.

8 Signs of Emerald Ash Borer

1. Thinning Canopy From the Top Down

The first thing most homeowners notice is a thin, patchy crown. Leaves at the top of the tree get sparse first, while the lower canopy still looks fine.

2. D-Shaped Exit Holes

When adult beetles chew their way out, they leave small holes about 1/8 inch wide with one flat side, like the letter D. These are the clearest sign of EAB.

3. S-Shaped Tunnels Under the Bark

Where bark is loose or split, you may see winding, S-shaped tunnels packed with fine sawdust. These are the feeding galleries of the larvae.

4. Vertical Bark Splits

The tree’s bark may crack in long vertical splits over the tunnels.

5. Heavy Woodpecker Damage

Woodpeckers love EAB larvae. Patches of lighter-colored bark where woodpeckers have stripped the outer layer are a strong clue.

6. Shoots Sprouting From the Trunk

Stressed ash trees often push out clusters of new shoots low on the trunk or near the base.

7. Early Leaf Drop or Yellowing

Leaves may yellow or drop earlier than on healthy ash trees nearby.

8. Dead Branches in the Upper Canopy

As damage spreads, more and more upper branches die. A tree with half its crown dead is usually past saving. Read more about the general signs your tree is dying.

Treat or Remove? How to Decide

Not every infested ash has to come down right away. A good rule of thumb:

• Less than about 30 percent canopy loss: a healthy, valuable ash may be protected with treatment applied by a licensed professional. Treatment has to be repeated over time.
• More than about 50 percent canopy loss: the tree is usually too far gone, and removal is the safer choice.
• Dead or nearly dead ash: remove it soon, before it turns brittle.

Location matters too. An ash leaning over your house, driveway, or a play area is a much bigger risk than one at the back of a large lot.

Why Dead Ash Trees Are So Dangerous

Ash killed by emerald ash borer dries out and becomes brittle much faster than many other trees. That causes two big problems:

• Limbs drop without warning, even on calm days, and heavy snow or wind can bring down the whole top.
• The tree gets harder to remove. Brittle wood can’t hold a climber safely, so crews may need a bucket truck or crane. Waiting usually makes removal riskier and more expensive.

If a dead ash is near your home, consider hazardous tree removal before the next storm.

What Ash Tree Removal Involves

1. Free estimate: a pro checks the tree, the damage, and what’s underneath it.
2. Sectional removal: the crew takes the tree down in small pieces, lowering limbs with ropes or using a crane for large trees.
3. Proper disposal: infested wood is chipped or hauled away so the beetle doesn’t spread.
4. Stump grinding (optional): the stump is ground below the surface so you can replant. Learn more about stump grinding.

In the Denver area, removing an ash tree usually costs about $400 to $1,500, with large or very brittle trees costing more. These are ranges only; a free estimate gives you an exact price. See our page on dead tree removal for more details.

What to Plant After Removing an Ash Tree

Once your ash is gone, replant with a mix of tree species so one pest can’t wipe out your yard’s shade again. Choose trees suited to Colorado’s dry climate and plant them well away from your house, driveway, and power lines.

FAQs About Emerald Ash Borer

Worried About Your Ash Tree?

Call Tree Removal Denver at (983) 277-2893 for a free estimate. We connect Denver-area homeowners with licensed, insured local crews for safe dead ash tree removal, 24/7.

Need a different job done? See everything we cover for tree removal service in Denver, from single trees to storm cleanup across the metro area.