Emerald Ash Borer (EAB), an invasive pest known to cause extensive damage to ash trees, has been confirmed in the city of Aurora.
Why does it matter?
A non-native pest with no natural predators, EAB poses a serious threat to urban forests in Colorado. The species tunnels under the bark of ash trees, which disrupts the tree’s ability to transport water and nutrients. Once infested by EAB, ash trees will weaken over time, increasing both the risk of damage to people and property as well as the cost of removal. Trees can then die in as early as two to four years
What is the city of Aurora doing about it?
In response to the confirmation of EAB’s presence, the city of Aurora is focusing on replacing ash trees to help protect our urban forest for the future. Planting new, diverse trees is the best way to reduce the damage caused by EAB and make Aurora's tree canopy stronger over time. While this approach intends to reduce the food source for the pest and combat its spread, it additionally provides a cost-effective strategy for the city.
"In Aurora, we’ve been proactive about Emerald Ash Borer from the start,” Adrian Camacho, manager of Open Space and Forestry said. “Since first learning about its spread in Boulder, we’ve followed a clear strategy: tree diversity is the best defense against invasive pests. Over the past decade, we’ve reduced our ash population from about 7,000 to 4,500, and we’ll keep moving in that direction.”
The estimated 4,500 ash trees owned by the city of Aurora comprise about 5% percent of the overall ash population. The majority of ash trees are located on private land.
“The reality is that nearly every infected ash dies, often becoming brittle quickly,” Camacho said. “Acting early makes removal and replacement safer and more cost-effective."
What do residents need to do about ash trees on their private property?
Residents with ash trees located on their property are encouraged to consider their options related to EAB, which include removal, replacement, or preventative insecticide treatment.
The city of Aurora has compiled educational resources and a list of licensed local arborists available for EAB consultation at
AuroraGov.org/EAB.
Here are the actions that residents can start taking today:
- Determine now if there are any ash trees on your property. Identifying features of ash trees include compound leaves with five to nine leaflets; leaflets, buds and branches growing directly opposite from one another; and diamond-shaped bark ridges on mature trees.
- If you have an ash tree on your property, start planning. Decide if the overall health of the tree merits current or future treatment or if it would be best removed and replaced with a different species. If you're unsure or decide the tree is worth saving and need pesticide treatment, make sure to work with a licensed arborist.
- Regularly inspect existing/remaining ash trees for signs of EAB infestation. Property owners with private 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.
- Be aware of EAB imposters. Other insects like lilac/ash borer, ash bark beetle and flat-headed apple tree borer may look like EAB or cause similar tree symptoms. For more information, visit
eabcolorado.com.
Help prevent further spread of EAB. When removing ash trees, chip the wood smaller than one inch. Do not transport ash tree remains, hardwood firewood or any other untreated ash wood products to other locations. Use local firewood only.
How did EAB get here?
Prior to its arrival in Aurora, EAB was first detected in Colorado when it appeared in Boulder in 2013. It has since continued to spread across the Front Range, including Denver’s discovery of the species in June. It is unknown whether EAB arrived in Aurora by natural spread or via accidental human transport, such as in firewood or other raw ash material.
In response to the 2013 identification of EAB, many Front Range communities put EAB management plans in place, including Aurora. The city of Aurora began an inventory and assessment of all city-owned ash trees in 2020. Since that time, no new ash trees have been planted by the city, and unhealthy ash trees are being removed and replaced with new species.
For more information about ash tree identification, the symptoms of EAB and treatment options, go to AuroraGov.org/EAB, eabcolorado.com or csfs.colostate.edu/emerald-ash-borer.