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Has the emerald ash borer (EAB) arrived in Denver?

Maybe. In 2013, the emerald ash borer (EAB) was found in Boulder. In August of 2019, it was confirmed in Broomfield. However, while it has not yet been detected in Denver, it could be here already. It often takes two to four years for signs of EAB infestation to manifest.

How much of Denver’s urban forest consists of ash trees?

The EAB has the potential to destroy Metro Denver’s 1.45 million ash trees (330,000 or 1 in 6 trees – in the City and County of Denver). Due to their fast growth and high aesthetic appeal, ash trees have been widely planted in Denver, including on private property, public parks, and other community areas.

Why should I care about Denver’s tree canopy?

Trees are critically important to our overall quality of life. Among other things, they produce oxygen, reduce smog, cool our neighborhoods and homes, and increase our property values. 

1 in 6 trees in Denver are ash trees. And if we do nothing, it’s just a matter of time before they’ll ALL be devoured by the emerald ash borer.

What does the EAB look like?

As you can see in various images, the EAB is an attractive insect with a dark, metallic-green body and a coppery-red or purple abdomen under its wings. To give you some perspective, at approximately ½-inch long, the EAB can fit comfortably on a penny.

Are there other insects that are similar in appearance to the EAB?

There are several insects native to Colorado that one could easily mistake for the EAB. There are even some other types of insects that tunnel into ash trees. 

That’s why Being a Smart Ash is about more than just being informed; it’s about being cognizant of what you don’t know. If you are unsure about the possible presence of the EAB in or on an ash tree, call the Office of the City Forester, an arborist or other tree care professional.

What are signs that an ash has been attacked by the EAB?

There are several telltale signs of EAB infestation. S-shaped tunnels can be seen on the trunk and tiny, D-shaped exit holes are often visible. Additionally, impacted trees show signs of thinning and bark shedding. Dying ash trees also attract Northern Flickers, a type of large, brown woodpecker. It can take 2-4 years for trees to show signs of infestation.

Can I keep my ash tree?

Yes! Denver residents who want to keep their ash trees should work with a licensed and insured arborist or tree service company on a treatment plan, which is 90 percent effective. Treatment must be repeated every 2-3 years. Choose from this list of approved tree services and get information about state licensing.

Are there other options besides treatment?

Given the serious threat posed by the EAB, removing and replacing ash trees is a viable option. In fact, depending on the size and location of the tree, replacement may be the smartest choice. Dead or alive, ash trees can be safely removed by a licensed and insured arborist or tree service company. Denver residents can also apply for a free replacement tree.

Is ash still a viable choice when considering what to plant in my yard?

The short answer is no. Bottom line: further planting of ash trees in Colorado is not recommended. The planting of diverse tree species in your yard or in your community is highly encouraged, as this is our urban canopy’s best defense against the majority of tree health problems. The Office of the City Forester has created a list of approved trees.

What is the City doing to combat this problem?

The Office of the City Forester, part of Denver Parks and Recreation, is in it for the long haul and is 100 percent committed to battling the EAB. It has already taken the first, big step by creating the 5-year Be A Smart Ash campaign ( Through this campaign, the City Forester is actively educating and turning Denver residents into Smart Ashes who can identify, treat, and/or replace their ash trees both now and over the course of the next 15 years.

Additionally, the City will replace poor condition and dead small ash trees from city-maintained land, including parks, and a few select right-of-way ash trees. Homeowners eligible for right-of-way removal and replacement will be contacted by the Office of the City Forester.

The Office of the City Forester is also offering free replacement trees to Denver residents.

How can Denver residents become Smart Ashes?

Being a Smart Ash is as easy as 1-2-3:

1.     Identify ash trees, regularly inspect for signs of the EAB, and contact the Office of the City Forester immediately at or (720) 913-0651 if trees display any symptoms of EAB infestation. 

2.     Talk to neighbors, friends, and co-workers about the EAB. Spread the word and encourage people to visit for more information.

3.     Do not transport firewood or other products from ash trees, as EAB larvae stealthily survive and travel hidden under the bark. If an ash tree absolutely has to be moved, the wood must be chipped smaller than one inch.