Emerald Ash Borer will Ruin our Urban Forest

The Emerald Ash Borer, first discovered in Boulder in 2013, is considered the most destructive pest in North America.

Emerald Ash Borer size
The future looks bleak for ash trees in the South Platte drainage area of Colorado.

The tiny Emerald Ash Borer (EAB) is such a destructive insect pest that it will most likely ruin the urban forest as it destroys unprotected ash trees in our area.

EAB has caused the death or decline of tens of millions of ash trees in 20 states. Now it’s in Colorado.

First discovered in Boulder in 2013, EAB most likely found its way to Colorado from the Midwest in a load of firewood. So far, Colorado is the farthest state west where the EAB has traveled, according to Dr. Whitney Cranshaw of Colorado State University.

“It’s a real tragedy because it will ruin an urban forest species in an extinction event,” he says.

In his estimation, EAB will eventually cost Denver a billion dollars to either treat ash trees or cut them down and replace them. All communities where it’s discovered will have to make difficult choices for treating, removing or replacing ash trees.

Right now, home owners and urban foresters in Boulder are planning how they’ll attack the problem this season. The pest has likely been in this area for about five years.

Within 10 years, other communities throughout the South Platte drainage will need to take action, too.

All those with ash trees in Boulder will have to decide this season whether to treat their trees with insecticides while balancing costs, environmental hazards, effectiveness of insecticides and the ease of application. There are no easy or inexpensive options.

“If you want to save the tree, you can treat it, but it will cost money,” Cranshaw explains.

If you live outside of Boulder you need to be aware that EAB is coming, locate the ash trees on your property, and look for signs and symptoms. If you find an adult beetle, it’s important to take it to a CSU Extension office for identification to help locate areas where the pest is present.

Some signs of infestation include:

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

Because it’s inevitable that EAB will find its way to ash trees in the South Platte drainage area, it’s important to stay vigilant, Cranshaw says.

Resources for more information include CSU’s Department of Bioagricultural Sciences and Pest Management website and the Colorado Department of Agriculture EAB website that includes an Ash Tree Zone interactive map and a way to sign up for the EAB newsletter to stay informed.


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