The Emerald Ash Borer (EAB) is a small, metallic green beetle with a widely notorious reputation, and not in a good way. Since its discovery in Michigan in 2002, it has killed over 100 million ash trees across North America.
Originally from Asia, the EAB likely arrived in wood packing materials and has since spread to 37 states. In Colorado, researchers first detected it in Boulder in 2013, and it has steadily expanded along the Front Range. It has even been found as far west as Carbondale.
As of early 2026, the EAB has not been detected in the Pikes Peak region. However, its continued spread makes future arrival likely.
And here is the major concern. Over 15 percent of Colorado’s urban canopy could be at risk.
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TL;DR: What is Emerald Ash Borer (EAB), and is it a threat to my trees?
Answer:
Why Ash Trees Are in Trouble?
The EAB doesn’t just nibble on trees. It shuts down their entire life support system.
The larvae feed beneath the bark, creating winding, S-shaped tunnels that block the flow of water and nutrients. Think of it like cutting off a tree’s plumbing and food supply at the same time.
Even worse, ash trees can look healthy for 2 to 4 years after infestation. This means damage is often underway before anyone notices.
How to Identify an Ash Tree
Not sure if you even have an ash tree? You are not alone. Ash trees are extremely common across Colorado, even though they are not native to the region.
Green and white ash are widely planted along streets, in parks, and in residential neighborhoods because of their hardiness, steady shade, and bright striking fall colors. In many communities, they make up a significant portion of the urban landscape.
Ash trees have a few defining characteristics that make them easier to identify once you know what to look for. Their branches grow opposite each other. They come out in pairs across from one another, not alternating.
Their leaves are compound, typically made up of 5 to 11 individual leaflets. As the tree matures, the bark develops a gray color with distinct diamond-shaped ridges.
If your tree checks these boxes, there is a good chance you are looking at an ash. And if that is the case, it is worth keeping a closer eye on it as Emerald Ash Borer continues to spread.
Signs of Emerald Ash Borer Infestation
EAB can be difficult to detect early, here’s what to keep an eye out for:
- Thinning canopy, especially in the upper portion of the tree
- Dead or dying branches
- Vertical cracks or splitting in the bark
- Increased woodpecker activity
- Small D-shaped exit holes in the bark
- S-shaped tunnels beneath the bark
- New shoots forming at the base of the tree, also called epicormic growth
Important note: Other stressors or pests can cause some of these symptoms. A professional inspection is the best way to confirm what is actually going on.
Treatment Options: Can You Save an Ash Tree?
Short answer: Yes. IF you act early.
Treatment is focused on protecting healthy trees before damage becomes severe. Options include:
- Systemic insecticides applied through soil or trunk injections
- Products containing imidacloprid, which can provide some control
- Trunk injections with emamectin benzoate, which offer the most effective and long-lasting protection
Most treatments are applied on a one to two year cycle depending on the product and tree size. Timing matters. Waiting until visible damage appears can be too late.
When Removal Makes More Sense
If an ash tree is heavily infested or already in decline, treatment may no longer be effective. In these cases, removal is often the safest and most practical choice.
Many property owners choose a balanced approach. They preserve high-value trees while removing and replacing others. This helps maintain a healthy and diverse landscape over time.
Planning Ahead: Protecting Your Trees and Colorado’s Urban Forest
Even though Emerald Ash Borer has not officially reached every community, preparation is already underway, and for good reason. Its spread across Colorado continues. Taking action early can make a big difference in how your landscape is affected.
If you have ash trees on your property, now is the time to start paying closer attention. That means you should identify your trees, check their health each year, and know what infestation signs to watch for. It is important to talk to a certified arborist. They can inspect your trees and help you decide whether preventive treatment is a good idea.
For the most up-to-date information on where Emerald Ash Borer has been confirmed in Colorado, you can view the Colorado State Forest Service’s interactive detection map. This tool is regularly updated and shows how the insect continues to spread across the Front Range and beyond.
Concerned about your ash trees or want a professional assessment?
The EAB is a serious threat, but it is not a lost cause. With early detection, proper treatment, and careful planning, we can save many of Colorado’s ash trees. Communities can avoid the widespread canopy loss seen in other parts of the country.
If you have ash trees, the best move right now is simple. Know what you have, watch for signs, and have a plan.