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What Coloradans Need To Know About Emerald Ash Borer

Colorado State Forest Service
Emerald ash borer larva

As spring weather gets warmer and plants start to bloom, it’s also the time for insects living within Colorado trees to awaken and emerge. One of these in particular, the invasive, tree-killing emerald ash borer is especially concerning to foresters since the insect’s target – the ash tree – is widespread along the Front Range.

Because the pest can go virtually undetected for the first few years of an infestation, forest authorities want the public’s help in containing the spread.

Update 4.14.2015 via Colorado Department of Agriculture:

EAB has been confirmed in 11 grids covering an area of 11 square miles within the City of Boulder. 2014-2015 new detections include portions of the University of Colorado campus and grid sections directly adjacent to the original 5 square miles where EAB was detected in 2013. To date, EAB has not yet been detected outside of the City of Boulder.

Credit USDA
Updated map as of April 2015 for the emerald ash borer in Boulder.

Our original post continues below:

The emerald ash borer has killed millions of ash trees in 25 states, especially in the Midwest and near the Great Lakes. It was confirmed in Boulder in September 2013, where officials quickly established a quarantine and began removing about a half-dozen trees.

So far EAB hasn't been detected outside the Boulder city limits, but that hasn't stopped Loveland from preemptively removing their ash trees.  Dr. Dan West, an entomologist with the Colorado State Forest Service, noted that trees can be infested for up to three or more years without showing signs.

"This is a very difficult pest to detect early on, and when populations are low or they’re first starting to build like they would be in and around Boulder, it’s very difficult," West said. "That’s part of why we’re trying to get the message out."

An estimated 15 to 20 percent of urban and community trees are ash, and many Front Range yards have them, too.  West - who is also part of the Colorado EAB Response Team - says now is the time for homeowners to determine what they want to do about any ash trees they may have on their property.

"I would have a plan in place before emerald ash borer showed up in my neighborhood," West said, "so that perhaps when [it] does come through, my landscaping or my yard is more resilient or in an area where it would come back if that ash tree were lost."

Credit Courtesy of Colorado State Forest Service
Courtesy of Colorado State Forest Service
D-shaped exit holes made by the emerald ash borer

The first step to creating a plan is to identify ash trees [.pdf]. Next, evaluate the tree’s condition for signs of EAB infestation:

Does it have dead branches, fading foliage, thinning around the crown, or issues around pruning wounds?

Are there serpentine tunnels made by larvae under the bark, or D-shaped exit holes?

Are there new green sprouts on lower branches or lower trunk, or vertical splits in the bark?

Any increased woodpecker activity?


After that, West recommends considering the value a tree provides [.pdf] before making a decision to preemptively remove it.

"Trees provide all kinds of services for us," West said. "Most of us love trees here in the arid West because they provide shade in the summertime. They help cool our homes or cool our environment, which usually means we use less water on our yards. So I would determine whether that tree is in a location where it would be detrimental if that tree was lost."

What homeowners choose to do may depend on how close they are to the known infestation area in Boulder.

West says strategies range from simply monitoring trees for signs of EAB, to treating them with insecticides, to removing and replacing ash trees with other types of trees.

As the host of KUNC’s new program and podcast In the NoCo, I work closely with our producers and reporters to bring context and diverse perspectives to the important issues of the day. Northern Colorado is such a diverse and growing region, brimming with history, culture, music, education, civic engagement, and amazing outdoor recreation. I love finding the stories and voices that reflect what makes NoCo such an extraordinary place to live.
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