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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, Littleton, Lyons, Superior, Broomfield, Westminster, Erie, Arvada, Thornton and Carbondale.
  • 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 The EAB quarantine around Boulder County was repealed effective Dec. 30, 2019.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 Littleton (June 2023) and Carbondale (June 2023). 

Contact Us About EAB

Dan West
CSFS Entomologist
Dan.West@colostate.edu

EAB News

emerald ash borer

Emerald Ash Borer on the Move Along Front Range

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

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Emerald Ash Borer Detected in Broomfield

BROOMFIELD, Colo. – National and state experts have confirmed the presence of emerald ash borer (EAB) – an invasive, highly destructive tree pest – in the City and County of Broomfield, northwest of Denver.

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Map powered by the Colorado Forest Atlas from the Colorado State Forest Service