Emerald Ash Borer

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.

Serpentine tunnels produced by larvae under bark

Emerald ash borer larva found in ash tree

D-shaped exit holes (left); serpentine tunnels or galleries (right) in ash tree

Branch peeling to identify EAB. Boulder, Dec. 2014

Emerald ash borer (Agrilus planipennis; EAB) is an insect native to Asia and introduced into North America sometime during the 1990’s. 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% 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.

2017-18 Highlights

The entire City of Boulder was presumed infested at the close of 2015.
Emerald Ash Borer was confirmed in the City of Lafayette in 2017.
Emerald Ash Borer was confirmed in the cities of Lyons and Superior in 2018.
Emerald Ash Borer has been confirmed in the cities of Boulder, Gunbarrel, Longmont, Lafayette, Lyons and Superior.

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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, visit our EAB: What Can You Do page.