Emerald Ash Borer


Two ash trees in Boulder were found in September 2013 to be infested with Emerald Ash Borer (EAB).  This borer was first identified in Michigan in 2002; since then it has spread to 22 states which now include Colorado. The most likely route of introduction to Colorado was in firewood or nursery stock.

May 28, 2015: According to City of Boulder Forestry, EAB adults have resumed emergence, now that sunny weather has returned. Photos of the different life stages found during peeling of branches and visual inspection of trees in mid May are below.  Now is the time to be looking for adults feeding on leaves.

EAB larvae Adult EAB prior to emerging  EAB adult EAB adult feeding damage

Ash tree affected by EABDo you your trees have Emerald Ash Borer?

Use this diagnostic tool from the Colorado Department of Agriculture (CDA) to  determine if you your trees show signs of Emerald Ash Borer.

Visit www.eabcolorado.com to learn more about this borer, the potential for damage to ash trees in Colorado and options for control.

Webinars about EAB are available on-demand through Emerald Ash Borer University.

About Emerald Ash Borer (EAB)

  • EAB impacts all species of ash (Fraxinus spp.), white, purple, green and their cultivars.
  • This insect is very difficult to detect because it is under the bark and the adults are only around from May to September. 
  • Larvae feed under the bark, eventually girdling the tree and cutting off nutrients.
  • Trees are typically killed within 2-4 years of first symptoms, even previously health trees.
  • Trees of all size can be attacked, from 1/2 inch saplings to largest mature trees.

Impact on Colorado
Colorado has many ash in the urban forest - estimates are that ca.15% of urban trees are ash. Boulder has approximately 98,000 public and private ash trees. The Denver Metro area has an estimated 1.45 million ash trees. Trees in some neighborhoods and developments may be as many as 80% ash.

    Potential Impacts of Emerald Ash Borer to Colorado Communities

        • Green and White Ash were widely planted in Colorado during the past 50 years.
        • Ash comprises 15%-80% of community trees, depending on location.
        • Ash is still planted extensively due to tolerance of urban growing conditions; it is fast-growing and is desirable for its fall color.
        • Ash is also naturalized along creeks and ditches throughout eastern Colorado and parts of the Front Range.


Infestations result from movement of infested ash trees and wood. The ash borer does not fly far on its own. Some of the items it moves on or in include:

  • Firewood
  • Packing material/industrial wood material
  • Live plant material (nursery stock etc)
  • Ash wood such as logs, branches, chips, etc.
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