BROOMFIELD, Colo. – As the weather warms and Colorado’s trees begin to leaf out, insects living within these trees also will begin to stir. And with the invasive, tree-killing emerald ash borer (EAB) set to emerge later this spring, now is the time for those living in or near Boulder County to determine what, if anything, they want to do about any ash trees on their property.

EAB, a non-native pest responsible for the death of millions of ash trees in 25 states, was confirmed in the City of Boulder in September 2013. The exotic pest has become a concern for communities all over Colorado, because an estimated 15 percent or more of all urban and community trees in the state are ash (genus Fraxinus).

Although EAB has not been detected in the state outside the City of Boulder, each year the insects can fly up to a half-mile from where they emerge to infest new trees. Also, there is the ever-present risk of EAB relocating via human transport of wood – especially within the existing quarantine established for Boulder County and surrounding areas.

First Steps & Strategies

Dan West, forest entomologist for the Colorado State Forest Service, says that while there are effective insecticides available to protect ash trees from EAB, other management strategies also exist for dealing with the pest. These include monitoring trees for the presence of EAB, removing or replacing ash trees before EAB’s arrival, and planting diverse new tree species in an effort to get them established now.

“The decision about whether to chemically treat your ash trees is a personal preference. The closer any ash trees are to the known infestation, the higher the risk that they will become infested by EAB,” said West, who also is an entomologist on the interagency Colorado EAB Response Team.

He says that the first step is for landowners to determine if they actually have any ash trees on their property. If they do, they should examine the tree for general health and signs of EAB, including D-shaped exit holes 1/8-inch wide, serpentine tunnels under the bark and new sprouts on the lower trunk. He also warns that it is possible for EAB to infest an ash tree for up to four years before visible signs of decline in the tree occur.

“Consider the overall health and value of each tree, and talk to a professional forester or arborist before applying any treatment,” West says.

For an updated map showing where EAB has been detected in Colorado, and for more information about ash tree identification, the symptoms of EAB and treatment options, go to

EAB: What Coloradans Need to Know

  • Learn how to identify ash trees, and signs of EAB infestation in ash trees:
    • 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
  • Multiple EAB management strategies exist for homeowners and communities, including monitoring trees for the early presence of the pest, removing and/or replacing ash trees, protecting trees with insecticides and planting new trees nearby in an effort to get them established before the arrival of EAB. The closer ash trees are to an area of known EAB infestation, the higher the risk that they will become infested.
  • If hiring someone to apply pesticide treatments to protect ash trees, the applicator must be licensed by the Colorado Department of Agriculture as a Commercial Pesticide Applicator.
  • Never transport firewood or other products from ash trees, as this is the most likely method of accidental spread. A quarantine is now in place in Boulder County and surrounding areas to try and prevent the human-assisted spread of EAB.

Learn More

For current information about EAB in Colorado, including the current quarantine in Boulder County and surrounding areas, go to If you think you have EAB in your ash trees, please contact the Colorado Department of Agriculture at (888) 248-5535 or email