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Science-based gardening information for Colorado communities from CSU Extension, Denver Botanic Gardens, and Green Industries of Colorado.

1499c – Emerald Ash Borer in Colorado   arrow

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Emerald Ash Borer on penny for size comparison

What is the Emerald Ash Borer?

Emerald Ash Borer (EAB), detected in Boulder, CO, in September 2013, is a nonnative insect with no natural enemies to keep it in check. The emerald ash borer is a small, green metallic beetle first detected in North America in 2002 in southeastern Michigan. The adult beetle is approximately one-half inch long with a metallic green head and back; the abdomen is coppery-purple in color. The larvae are up to one-half inch long, have prominent bell-shaped segments and are creamy-white in color.

What do Emerald Ash Borers attack?

The emerald ash borer attacks only ash trees, and all ash species – including green, white, black and blue – and the pest is responsible for the death and decline of tens of millions of ash trees in the United States. Colorado has many ash trees in the urban forest (it’s estimated about 15% of urban trees are ash). Ash trees are popular in Colorado with an estimated 98,000 in the city of Boulder alone; the Denver Metro area has an estimated 1.45 million ash trees. As of early 2014, the only confirmed EAB infestations in Colorado are in Boulder County.

What are signs that a tree is being attacked?

It is possible that EAB could infest an ash tree for three or four years before signs of tree decline are visible. Infestation signs include:

  • Sparse leaves or branches in the upper part of the tree with D-shaped exit holes about 1/8 inch wide
  • New sprouts on the lower trunk or lower branches
  • Vertical splits in the bark
  • Winding S-shaped tunnels under the bark
  • Increased woodpecker activity

Note that drought and general urban stress of Colorado’s ash trees may mimic EAB symptoms. However, if an ash tree is experiencing die-back or looking unhealthy, residents are encouraged to have it examined by a professional tree company and contact the Colorado Department of Agriculture or their city or county forestry office.

Does Colorado have any restrictions surrounding Emerald Ash Borers?

Since November 2013, a quarantine has been in effect in Boulder County , the town of Erie, and three other small parcels of land adjacent to Boulder County in Colorado. The quarantine prohibits any ash products (including logs and green lumber, nursery stock, scion wood and bud wood, chips and mulch, stumps, roots and branches) and all hardwood firewood from leaving the quarantined area. Movement of ash products within the quarantine area is permitted.
For the quarantine map and additional information, please visit the Colorado Department of Agriculture’s emerald ash borer website at

For more information, see the following references:

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