Emerald ash borer (EAB) is an invasive beetle whose larvae feed beneath the bark of ash trees. The damage interrupts the movement of water and nutrients, and untreated trees can decline and die. Colorado homeowners can help protect valuable ash trees by identifying them early, watching for signs of decline, and getting advice from a qualified tree-care professional.
What trees can emerald ash borer attack?
EAB attacks ash trees in the genus Fraxinus. If you are not sure whether a tree is an ash, ask an arborist or use a reliable tree-identification resource before deciding on treatment.
EAB has been established in the Denver metro area since it was first detected in Colorado in 2013. Its presence does not mean every ash tree is infested, but owners should monitor ash trees and follow current guidance from Colorado State University Extension and the Colorado Department of Agriculture.
Signs to look for
EAB can be difficult to detect early. Possible signs include:
- D-shaped exit holes in the bark, roughly 1/8 inch across.
- Thinning foliage or branch dieback, often beginning in the upper canopy.
- New shoots growing from the trunk or larger branches.
- Bark splitting or areas where woodpeckers have removed bark while feeding on larvae.
These symptoms can have other causes. Do not peel bark from a tree to look for larvae; have a qualified professional inspect it.
Treatment or removal?
Treatment decisions depend on the tree’s condition, size, location, and value, as well as local EAB pressure. Trunk-injected insecticides can protect some healthy or lightly infested ash trees, but treatment is not appropriate for every tree and often needs to be repeated on a professional schedule. A certified arborist can explain the options, expected costs, and likelihood of success for your tree.
If a tree is severely declining or structurally unsafe, removal may be appropriate. Removing one infested tree does not stop EAB from spreading in an area where it is already established. Ask your local authority or tree-care professional how to handle and transport ash wood; rules can change. Do not move firewood unless you have checked current restrictions.
Help slow its spread
- Avoid moving firewood over long distances. Buy wood near where it will be burned and follow current state and local rules.
- Inspect ash trees regularly, especially during the growing season.
- Report suspected EAB through the current reporting channel listed by the Colorado Department of Agriculture.
- If replacing an ash, choose a different suitable species and avoid planting a single species throughout a landscape.
What to do next
- Confirm which trees on your property are ash.
- Look for canopy thinning, dieback, exit holes, and other signs, without cutting or peeling bark.
- If you see concerning symptoms, arrange an inspection by a qualified arborist familiar with EAB.
- Check current Colorado Department of Agriculture and Colorado State University Extension guidance before treating, removing, or transporting ash wood.
Early identification gives you more time to make an informed decision. A site-specific assessment can help determine whether monitoring, treatment, or removal is the best option for your tree.