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A green ash tree in a Colorado neighborhood
Ash trees were widely planted in Colorado urban neighborhoods.

Emerald ash borer (Agrilus planipennis; EAB) is an insect native to Asia. It was introduced into North America sometime during the 1990s, probably via ash wood pallets or wood packing material.

Since its initial discovery in southeastern Michigan in 2002, this insect has killed millions of ash trees (Fraxinus spp.) throughout the central and northeastern United States and Canada. EAB is now considered the most destructive tree insect pest ever to be introduced into North America.

An infestation was first detected in Colorado in the City of Boulder in September 2013. Approximately 15 percent of the trees in Colorado’s urban forests are ash, making this insect a major threat to urban forests statewide.

Where is EAB in Colorado?

  • EAB has been confirmed in unincorporated Larimer County and in the cities of Boulder, Gunbarrel, Longmont, Lafayette, Lyons, Superior, Broomfield, Westminster, Erie, Arvada and Thornton.
  • The entire City of Boulder was presumed infested at the close of 2015.
  • In 2019, EAB was confirmed in the City of Broomfield, the first confirmation in Colorado outside of a federal quarantine, and (for the first time) in unincorporated Larimer County. The EAB quarantine around Boulder County was repealed effective Dec. 30, 2019.
  • The most recent confirmed detections have been in Erie (June 2021) and Thornton (June 2022).

Contact Us About EAB

Dana Coelho
CSFS Urban and Community Forestry Manager

Dan West
CSFS Entomologist