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.

No, emerald ash borer has not been found in Highlands Ranch. However, detecting emerald ash borer can be difficult when pest populations are small. Damage to trees is hidden under the bark and tree decline is gradual. Due to the many instances found in surrounding areas, the Metro District assumes it has reached Highlands Ranch trees.

Emerald ash borer was first found in Boulder in September 2013. Since then it has also been detected in Arvada, Aurora, Berthoud, Broomfield, Carbondale, Centennial, Denver, Edgewater, Erie, Fort Collins, Golden, Gunbarrel, Lafayette, Lakewood, Littleton, Longmont, Louisville, Loveland, Lyons, Superior, Thornton, Westminster, and Wheat Ridge. In 2026, the first instance documented in Douglas County was found in Parker. 

The insect is expected to spread in upcoming years. It was originally detected in Michigan in 2002 and has since been confirmed in 36 states.

• Staying in tune with regional trends, the Metro District forestry team hasn't planted any new ash trees in Highlands Ranch in at least 15-20 years. Tree diversity is a priority for any new tree plantings, which benefits the health of our overall urban forest.
• As occurrences of emerald ash borer were confirmed closer to our community, the forestry team prioritized high value, healthy ash trees for treatment. These high priority trees include large trees in Metro District parks that shade ballfields, playgrounds and other spots frequently used by visitors. Trees are treated by forestry staff with injections or trunk sprays as dictated by each situation. While a significant portion of park trees will be treated to protect against emerald ash borer, the majority of ash trees on Metro District property will not be treated.
• If any ash trees are suspected to have emerald ash borer, forestry technicians conduct branch sampling to look for signs of the insect. Emerald ash borer has not been found on Metro District property.
• Metro District foresters share information with our community to protect our urban forest. They are happy to answer questions or direct residents towards appropriate resources.

While the private and commercial population of ash trees in Highlands Ranch is difficult to pinpoint, the Metro District currently cares for 1,469 ash trees, which is about 10% of the total Metro District tree population.

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.

• Colorado State Forest Service and Colorado State University Extension offers a webpage with helpful resources for ash tree identification.

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.

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.

Symptoms of infestation 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

Symptoms of emerald ash borer 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.

When deciding if ash trees should be left alone, removed or treated:

1. Inventory your ash trees and determine how many you have and where they are located.
2. Figure out if some are worth saving:
   • Are the valuable to the landscape or owner?
   • Are they healthy and have few signs of EAB?
   • Are they located on the right site?
3. Consult with a reputable tree care professional to help evaluate your trees and treat those you'd like to save. Be sure to get at least two estimates, hire a certified licensed professional and ask for references and insurance.

Homeowners can also preemptively remove less desirable ash trees and replace them with more diverse species.

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.

• 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 die-back or appears unhealthy, have it examined by a professional.