In 2013, emerald ash borer (EAB) was confirmed for the first time in Colorado, in the City of Boulder. The highly destructive, non-native insect is responsible for the death or decline of millions of ash trees in more than 30 states and has already cost communities in the eastern U.S. billions of dollars to treat, remove and replace ash trees.

Emerald ash borer (Agrilus planipennis; EAB) is an insect native to Asia and introduced into North America sometime during the 1990s. Since its initial discovery in Michigan in 2002, this insect has killed millions of ash (Fraxinus spp.) trees throughout the central and northeastern United States and Canada. It is now considered the most destructive tree insect pest ever to be introduced into North America. An infestation was detected 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.

Signs & Symptoms

Many ash trees in Colorado are drought stressed and planted in alkaline soils. Determining an emerald ash borer presence is often difficult to the untrained eye. Symptoms include:

  • Sparse leaves or branches in the upper part of the tree
  • Vertical splits in bark possibly showing S-shaped galleries underneath
  • Increased woodpecker activity
  • Miniature leaves at the tips of branches late in the summer

For more detailed information about identifying ash trees, tips on what people can do about EAB, and other resources, please visit our Emerald Ash Borer (EAB) — A Green Menace page.

EAB Detections

  • EAB has been confirmed in unincorporated Larimer County and in the cities of Boulder, Gunbarrel, Longmont, Lafayette, Lyons, Superior, Broomfield and Westminster.
  • 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 in unincorporated Larimer County.

Learn more about EAB early dectection in words, images and maps by viewing the interactive story map below. For a larger version, visit our Emerald Ash Borer – Early Dectection Efforts page.

Management Options

The best management option depends on the value of the tree to a landowner, and the costs associated with each option. Options for treating at-risk or infest trees include removal, replacement and chemical treatments. For more information, select the What Can You Do button below.