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Emerald Ash Borer

Is there a quarantine from moving wood out of Boulder County?

As of 2020, not anymore, as state officials lifted it. What this means is Jefferson, Denver, and Adams County all likely have pockets of emerald ash borer and it will soon move down through Arapahoe.

What is the emerald ash borer (EAB) and what does it do?

Emerald ash borer (EAB) is an invasive beetle that infects and kills all North American true ash species including green, white, black, and blue ash and their cultivars. The larval stage of EAB feeds under the bark of trees, cutting off the flow of water and nutrients. Decline and death of the tree happen rapidly over a two to the four-year window once the ash tree is attacked.

Is there a way to prevent emerald ash borer from killing my ash tree?

There are several preventive tactics that have developed since the emerald ash borer was discovered in North America in 2002 and Colorado in 2013. 

Direct injection of special chemicals into the bark of the target ash is one type. A second way involves soaking the soil around the ash tree with a treatment that is injected into the soil around the target tree. Chemical treatments appear to work best when applied before the ash tree becomes infested with EAB – in addition, the effectiveness of treatments will depend on,

  • tree condition
  • time of the year
  • a systemic pesticide that is used. 

Within the county of Boulder, officials recommend an EAB preventive tree injection for ash trees in spring.  The city of Denver forester also recommends treating high-profile ash trees and the city has embarked on a high-profile “Be a Smart Ash” marketing campaign to promote the EAB prevention campaign. 

What should I be doing with my ash?

 CDA is recommending treatment on high-profile ash trees in Boulder, CO metro, and Denver metro.  High-profile trees, in layman’s terms, are valuable trees that you wouldn’t want to live without.  Here is an article further discussing how to decide if your ash tree is a high-profile tree

The main idea is that planning your yard or campus requires a realistic assessment based on goals and of course always limited by resources. Any tree can be preserved with the right amount of money. However, it may be that losing the tree and replacing is a better strategy. In some cases lower profile ash would be better replaced down the road, depending on its location, age, and condition.

What are the symptoms?

EAB adults live high in ash trees and can be difficult to detect. D-shaped holes, curved galleries (carvings under the bark marking the EAB path), and sudden decline of the tree are all diagnostic indicators. However, similar conditions can also be created by other borers, as well as a fungal disease called cytospora.  This can complicate detection and diagnosis.

Here is an article related to EAB symptoms.  The CDA has a hotline if you identify EAB in your ash tree.  Call Colorado Dept. of Agriculture 888-248-5535 to report. They are doing a survey to ID where EAB is in the state. This is a crucial step in helping decipher the footprint for EAB.

Will an emerald ash borer attack a mountain ash tree?

No, as mountain ash are not a true ash. Mountain ash has a different leaf structure than true ash trees and will also have fleshy, red-orange berries growing in the fall.


What are other ways to prevent the emerald ash borer from spreading?

Transporting firewood is the consensus pick as the main way EAB will travel and spread in Colorado. So, don’t transport ash for firewood.  One big difference for Colorado may lie in its ecosystem; Colorado does not have millions of acres of natural ash tree forests like Minnesota and Michigan, both of which are heavily infested. That means that there is no natural highway for EAB to spread. However, besides human transport of firewood infested with EAB, the beetle could get caught in higher elevation winds, transporting them beyond the range that they can reasonably fly on their own. This phenomenon was first witnessed during the mountain pine beetle epidemic of the 1990s and 2000s. And as always, alerting neighbors is another way to help stop the spread of EAB.

What responsibilities do private landowners have regarding emerald ash borer?

Private landowners have options about what steps to take if there are ash trees on the property. The City of Longmont will only treat city-owned ash trees. The City of Longmont recommends that residents take action now to evaluate treatment for their trees.

In the Denver area, the Be a Smart Ash program aims to teach residents to recognize if they have ash trees, the signs of the Emerald Ash Borer, and the dangers associated with the beetle. “The vast majority of ash trees in Denver are on private property. The city’s strategy is to educate our residents,” said Denver Forester Rob Davis.

To learn more about ash trees and this beetle, visit

Does Arborscape offer a free estimate for EAB prevention?

Always! It’s vital to have us or another qualified Denver tree service take a look at your ash tree to:

  • confirm the species of ash
  • determine whether the tree is infested yet
  • evaluate the general health and maintenance of the tree

The earlier you establish a treatment plan, the better the chances of an arborist being able to protect your tree. The tree service should have a Qualified Supervisor of Pesticide Applications on staff who is educated on the different treatment options and understands the pathology of tree diseases.  Engaging an amateur tree service that is not legally licensed by the State of Colorado will result in the only solution that they can provide; tree removal. It’s like the adage, “if the only solution you have is a hammer, every problem looks like a nail.”

Should you see EAB or need to schedule an evaluation, please contact us ASAP!

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