Emerald Ash Borer Update for Colorado Front Range Homeowners (2026)

If you have an ash tree in your yard, 2026 is the year to pay attention.

Emerald Ash Borer (EAB) continues to spread rapidly across Colorado's Front Range. Following major expansion during the 2025 season, Colorado State University and the Colorado State Forest Service now recommend that homeowners assume EAB is present in their community, even if it has not yet been officially confirmed in every neighborhood. More than 20 Front Range cities now have confirmed infestations, and the insect continues moving south each year. Once an ash tree becomes heavily infested, it typically dies within 2–4 years if left untreated.

What makes EAB so dangerous?

Unlike many native insects that primarily attack stressed trees, Emerald Ash Borer attacks healthy, vigorous ash trees. The larvae tunnel beneath the bark and feed on the living tissue that transports water and nutrients throughout the tree. Eventually, the tree is unable to move water from its roots to the canopy and slowly declines.

Early symptoms include:• Thinning leaves in the upper canopy• Increased woodpecker activity• Small D-shaped exit holes in the bark• Vertical bark splits• Numerous shoots growing from the trunk or lower branches

Unfortunately, by the time these symptoms become obvious, the infestation is often already well established.

Can ash trees be saved?

Yes—if treatment begins early enough.

Extensive university research continues to show that trunk injection with emamectin benzoate is the most effective treatment available for residential ash trees. When performed before severe decline occurs, it provides excellent protection for approximately two to three years and has consistently outperformed soil drenches and basal bark sprays, especially on mature landscape trees.

The key is timing. Preventive treatment is far more successful than waiting until a tree is already in serious decline.

Keeping ash trees healthy

While no amount of watering or fertilizing will stop Emerald Ash Borer by itself, healthy trees are better able to tolerate environmental stresses and recover from routine pruning and weather extremes.

Good tree care includes:🌳 Deep watering during dry periods🌳 Installing mulch rings within the root zone🌳 Avoiding soil compaction and root damage🌳 Correct structural pruning to improve wind and snow damage resistance🌳 Soil nutrient management where deficiencies exist🌳 Regular inspections by a qualified arborist

Colorado's alkaline soils commonly limit the availability of nutrients such as iron, manganese, sulfur and nitrogen. Correcting these deficiencies helps improve overall tree vigor, although it should always be considered a complement to EAB treatment—not a replacement.

What should homeowners do in 2026?

If you have an ash tree:✅ Have your ash tree inspected before symptoms become severe.✅ Begin preventive treatment if the tree is healthy and worth preserving.✅ Avoid moving ash firewood, which can spread the insect to new areas.✅ Develop a long-term management plan rather than waiting until the tree declines.

Ash trees provide valuable shade, reduce summer temperatures, improve air quality and add significant value to our neighborhoods. Many healthy ash trees can remain beautiful for decades with timely treatment and proper care.

If you're unsure whether your tree is an ash or whether treatment is appropriate, a professional assessment can help you make the most cost-effective decision before Emerald Ash Borer causes irreversible damage.

— Sea to Sky Arborist Solutions is ready to help Front Range homeowners make informed decisions about the health and longevity of their trees.