Emerald ash borer

After the first Colorado occurrence of emerald ash borer was discovered in 2013, more and more residents are concerned about this invasive species.

Useful links

How to identify emerald ash borer
How to identify ash trees
Emerald ash borer Quick Guide
Best tree species for Highlands Ranch

EAB01s EAB06s


Frequently asked questions

What is an emerald ash borer?

The emerald ash borer is a dark metallic green beetle approximately 1/2-inch long and 1/8-inch wide that is extremely destructive to ash trees. The insect species, native to parts of eastern Asia, was accidentally introduced to North America probably sometime in the 1990s. It is expected to ultimately kill almost every unprotected ash tree presently growing on the continent. It does not attack other types of trees.

Has emerald ash borer been found in Highlands Ranch?

No, emerald ash borer has not been found in Highlands Ranch. Emerald ash borer was first found in Boulder in September 2013. Since then it has also been detected in  the cities of Gunbarrel, Longmont, Lafayette, Lyons, Superior, Broomfield, Westminster and near Berthoud. The insect is expected to spread in upcoming years. It was originally detected in Michigan in 2002 and has since spread to 22 states.

What is the Highlands Ranch Metro District doing about emerald ash borer?

The Metro District’s Forestry department has been proactive in coordinating with the U. S. Department of Agriculture (USDA) on a branch sampling detection system for emerald ash borer. The USDA created a grid system dividing Highlands Ranch into one square mile quadrants. The forestry team has been pruning branches from ash trees in these areas and peeling back the bark looking for the presence of emerald ash borer. This data is shared with the USDA and placed in a statewide database for documentation.

Are ash trees prevalent in Highlands Ranch?

While the private and commercial population of ash trees in Highlands Ranch is difficult to pinpoint, the Highlands Ranch Metro District currently cares for 1,861 ash trees, which is 14% of the total Metro District tree population.

How can I tell if I have an ash tree?

Ash trees have compound leaves, meaning there are five to nine leaflets on each stalk. Leaflets are smooth or finely toothed along the edges. Seeds on female trees are paddle-shaped. Branches and buds grow in pairs, directly opposite from each other. Mature bark displays diamond-shaped ridges. The Colorado State Forest Service and Colorado State University Extension have released a free app, EAB/Ash Tree ID, that will allow anyone to use their mobile device to quickly ascertain whether a tree may be a potential target for the pest. The app can be found in app stores by searching for “ash tree.”

Colorado State Forest Service and Colorado State University Extension released a free app that will allow anyone to use their mobile device to quickly ascertain whether a tree may be a potential target.

I have treated my ash trees in the past for borers. Why is this a new problem?

There are several insects native to North America that tunnel into the trunks and limbs of ash, but the damage potential of the emerald ash borer far exceeds any of those other insects.

How does emerald ash borer kill ash trees?

The larval stage of the insect tunnels through the vascular system of the tree and cuts off the tree’s water and nutrient supply. It essentially “chokes” the tree and kills it from the top down.

What are some symptoms of emerald ash borer infestation?

Symptoms include sparse leaves or branches in the upper part of the tree, D-shaped exit holes about 1/8 inch wide, new sprouts on the lower trunk or lower branches, vertical splits in the bark, winding S-shaped tunnels under the bark, increased woodpecker activity.

Will symptoms show up right away?

Symptoms may not be evident for 2-3 years making early detection difficult. Emerald ash borer initially attacks along the upper trunk and branches causing the canopy to die back.

What happens to a tree after infestation?

Infested trees may lose up to 50% of the canopy in the first few years and die off within 3-5 years.

Should I start treating my trees now?

Since most emerald ash borer treatments provide control for one year or, at most, two years following application, there is no benefit in treating a tree prior to when emerald ash borer is present.

What should I do to prevent emerald ash borer infestation?

Homeowners can preemptively remove less desirable ash trees and replace them with more diverse species. Once emerald ash borer is confirmed in the area, you can also treat selective ash tree stands with trunk injection, trunk spray or soil applications. If left untreated, all ash trees will succumb to emerald ash borer.

How does emerald ash borer spread?

The insect spreads slowly on its own as the adult beetle can fly anywhere from short distances to about a half-mile. But most long-distance movement of emerald ash borer has been traced to the transport of infested firewood, logs or nursery trees.

What can I do to help?

Do not move firewood from one location to another – burn firewood where you buy it. Identify the trees on your property and give all trees good care. Educate yourself on how to recognize the signs and symptoms of emerald ash borer and monitor your ash trees throughout the year. If an ash tree is experiencing dieback or appears unhealthy, have it examined by a professional.

Back to top

Other helpful resources



*Photos courtesy of ForestryImages.org: David Cappaert, MSU;  William M. Ciesla, Forest Health Management International

©2020, Highlands Ranch Metro District | sitemap | web development