This ash tree is at risk from emerald ash borer sign. Photo: Ryan Lockwood

A Green Menace

Emerald ash borer attacks and kills all true native North American ash trees, including green, white, black and blue ash, and their cultivars (including “autumn purple ash,” a popular white ash varietal in Colorado). Although rare in Colorado, white fringetree (Chionanthus virginicus) also has now been documented as susceptible to EAB.

This pest kills stressed and healthy trees and is so aggressive that ash trees may die within two years after they become infested.

The 1/2-inch long, dark green adult beetles are active from late May through July, as they feed on ash trees and lay eggs on the bark. After hatching, the resulting EAB larvae tunnel into the bark to feed in the phloem and outer sapwood layers of the tree, producing galleries that girdle and ultimately kill the tree within two to four years. These expanding S-shaped galleries can be located when the bark is removed.

EAB adults typically fly up to a half-mile from where they emerge to infest new trees. Distribution of the pest over much longer distances is possible due to people transporting ash firewood, logs, nursery stock or other wood.

It is possible for EAB to infest an ash tree for up to four years before visible signs of decline in the tree occur.

The EAB/Ash Tree ID AppTo help identify ash trees, CSFS and Colorado State University Extension have developed a free app that will allow anyone to use their mobile device to quickly ascertain whether a tree may be a potential target for the pest.

The EAB/Ash Tree ID app works on most Apple and Android-based devices, and is available at Google Play and the Apple App Store.

An Emerging Threat to Community Trees

Emerald ash borer was first confirmed in North America in 2002 in southeastern Michigan. It likely arrived in the U.S. several years earlier, probably via ash wood pallets or wood packing material.

EAB now poses a serious threat to Colorado’s urban and community forests, where ash trees comprise an estimated 15 percent or more of all trees. The Metro Denver area alone has approximately 1.45 million ash trees, which provide an estimated $82 million annually in services including stormwater mitigation, energy savings and increased property values.

Although to date EAB has only been detected in Boulder County, it will not remain there. For communities on Colorado’s Front Range and northeast plains, it’s only a matter of time before this pest will arrive. And without ongoing treatment, any infested tree will die.

Everyone in Colorado can help fight this pest by not transporting hardwood firewood, because human-assisted spread is the only way it can move over long distances.

We’re only one piece of wood away from this showing up somewhere new.

~Dan West, CSFS Entomologist

What Do Ash Trees Look Like?

What We’re Doing

Since the initial detection of EAB in the state, the Colorado State Forest Service (CSFS) has worked with partner groups on the Colorado Emerald Ash Borer Response Team to take various actions to manage the spread of EAB in Colorado.

The Colorado EAB Response Team is comprised of members from the following agencies/organizations: Boulder County, City of Boulder, Colorado Department of Agriculture, Colorado State Forest Service, Colorado State University Extension, Colorado Tree Coalition, Green Industries of Colorado, University of Colorado and USDA Animal and Plant Health Inspection Service.

EAB Response Team Management Actions Include

  • Establishing a quarantine for Boulder County and surrounding areas
  • Conducting outreach efforts
  • Hosting EAB identification and branch-peeling workshops
  • Assisting communities with tree inventories to assess the ash tree population
  • Introducing biocontrol measures that target and kill EAB larvae
  • Implementing detection actions to try and locate EAB outside of Boulder

For more information about management efforts and the EAB Quarantine in Colorado, go to

Local Governments Managing for EAB

Click on the map for a larger view (PDF)

What Can You Do?

Learn How to Identify Ash Trees

The most important action homeowners all over Colorado can take now is simply determining if they have ash trees, which have:

  • compound leaves with 5 to 9 leaflets
  • leaflets, buds and branches growing directly opposite from one another
  • diamond-shaped bark ridges on mature trees

Know the Signs of EAB Infestation

Those who do have ash trees need to watch them for EAB symptoms, and have a plan in place for when the insect is detected in their area. Signs that a tree has EAB include:

  • thinning of leaves and upper branches and twigs
  • serpentine tunnels produced by larvae under the bark
  • D-shaped exit holes 1/8-inch wide
  • new sprouts on the lower trunk or lower branches
  • vertical splits in the bark
  • increased woodpecker activity

Be aware of EAB imposters. Other insects like lilac/ash borer, ash bark beetle and flat-headed appletree borer may look like EAB or cause similar tree symptoms.

If you think you have EAB in your ash trees, contact the Colorado Department of Agriculture at (888) 248-5535 or email

Avoid Planting Ash Trees

Ash trees have been widely planted in Colorado, but because EAB is always fatal to untreated ash trees, avoid planting any true ash species (genus Fraxinus). Instead, focus on tree and landscape-plant diversity. No one tree species should comprise more than 10 percent of the planted trees growing in any urban or community setting.

Now is a great time to ‘plant ahead’ and get new trees in the ground that can someday replace ash lost to EAB, and also replace the shade and other benefits they provide.

An ash tree replacement tool, which includes a list of trees suitable for ash replacement, is available on the Colorado Tree Coalition website at

Management Options for Homeowners

In Colorado, EAB has only been detected in the City of Boulder, but its further spread is imminent. While there are effective insecticides available to protect ash trees from EAB, other management strategies also exist for dealing with the pest, including:

  • monitoring trees for the presence of EAB,
  • removing and/or replacing ash trees, and
  • planting new trees preemptively in an effort to get them established before the arrival of EAB.

Decisions about how to manage ash trees should take into account the overall health of each tree and its value to the property owner.

The closer ash trees are to an area of known infestation, the higher the risk that they will become infested by EAB through natural spread. Also, trees within or near the EAB Quarantine area are at a higher risk of infestation through human-assisted spread of the pest, because infested wood can legally be moved throughout the area.

Consumers should educate themselves when purchasing chemical products to protect trees against EAB, and talk to a professional forester, Extension agent or arborist before applying any treatment.

More information about chemical treatment options.

Don’t Move Firewood!

Never transport hardwood firewood or any other raw wood products from ash trees, as this is the most likely method of accidental spread.

A quarantine is in place in Boulder County and surrounding areas to try and prevent the human-assisted spread of EAB. Regulated articles include EAB specimens, ash nursery stock, ash logs, branches and chips, green lumber, all hardwood firewood or any other article, product or means of conveyance that may present a risk of spreading EAB.

Learn More

For current information about the current quarantine in Boulder County and surrounding areas, visit

For more information about the dangers of moving firewood, visit

Videos – Ash Trees & Emerald Ash Borer

How to Identify an Ash Tree

Does My Tree Have Emerald Ash Borer?