Emerald Ash Borer is on the Move Along the Front Range

Emerald Ash Borer Adult - Photo courtesy of Dan West, CSFS

Colorado State Forest Service

With a new spring season in bloom in Colorado, trees are emerging from their winter dormancy period to bring life, color, and vibrancy to our communities. Trees, however, are not the only living things completing their overwintering period this spring.

Under the bark of ash trees along the northern Front Range, the larvae of emerald ash borer (EAB) are transforming into adult beetles that will emerge in May and June to infest new trees. First detected in Colorado in 2013 in the City of Boulder, EAB has spread to other cities and towns, with new detections last year in Arvada, Louisville, and north of Fort Collins in Larimer County.

EAB is on the move along the Front Range. With Emerald Ash Borer Awareness Week taking place this week, partners with the Colorado Emerald Ash Borer Response Team encourage residents to prepare for EAB and ‘plant ahead’ for the inevitable.

“Spring is an ideal time to plant trees in your yard or elsewhere in your community,” said Dana Coelho, Urban and Community Forestry Program Manager for the Colorado State Forest Service. “If you have an ash tree, consider planting a different tree now – but not another ash tree – to eventually replace that ash. It will take years for your new tree to reach maturity, so get it established now before EAB takes out your ash tree.”

With ash trees estimated to comprise 15 percent or more of all community trees in Colorado, EAB poses a serious threat to urban forests. Coelho advises residents on the Front Range to determine if they have ash trees on their property. If they are not sure if a tree is an ash, they should contact their local CSU Extension horticulture agent or a certified arborist who can accurately identify the tree and help them set a plan for it, such as removing and replacing it or treating it for EAB. In addition, the CSFS offers tips on selecting a tree care company to assist with EAB.

Coelho also said it is important for residents to plant a variety of trees on their property and in their neighborhoods to increase species diversity. “No one species should comprise more than 10 percent of the planted trees growing in any community setting,” she said. “That way, our urban forests are more resilient to diseases and insects like the emerald ash borer.”

Colorado residents, especially those living on the Front Range, are advised NOT to plant ash trees. The Colorado Tree Coalition offers online descriptions of trees suitable to plant throughout Colorado, plus a list of recommended trees to plant along the Front Range at www.coloradotrees.org.


EAB Tips for Front Range Residents

  • Determine now if you have any ash trees. Identifying features of ash trees include compound leaves with 5 to 9 leaflets; leaflets, buds, and branches growing directly opposite from one another; and diamond-shaped bark ridges on mature trees. More information about ash tree identification, including a helpful app, is at csfs.colostate.edu/eab.
  • If you have an ash tree, start planning. Decide if the overall health of the tree and the benefits it provides merit current or future treatment, or if it would be best to remove and replace it with a different species. If you are not sure, contact your local CSU Extension horticulture agent or an ISA Certified Arborist. If you do plan to treat the tree, the CSFS offers recommendations for selecting a tree care company.
  • Plant trees. Replace ash trees in poor health with diverse species. The Colorado Department of Agriculture offers a database of registered nurseries and landscape contractors.
  • Recognize signs of EAB infestation. Property owners with ash trees should be on the lookout for thinning of leaves in the upper tree canopy, 1/8-inch D-shaped holes on the bark, and vertical bark splitting with winding S-shaped tunnels underneath. Report suspect trees by calling the Colorado Department of Agriculture at 1-888-248-5535 or filling out their EAB Report Form at https://ag.colorado.gov/eab-identification-and-reporting.
  • Help prevent further spread of EAB. Do not transport ash or any hardwood firewood or any other untreated ash wood products to other locations outside the Front Range. Dispose of ash wood safely by chipping, composting, milling into lumber, or taking it to a landfill.

For more information about ash tree identification, the symptoms of EAB, treatment options, and how to use ash wood, go to csfs.colostate.edu/eab.

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