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Invasion of emerald ash borer spreads in Colorado

Ash trees on the Colorado Front Range are healthy as ever after a huge dose of spring rain, but emerald ash borer is still spreading.

DENVER — It’s estimated that 1 out of every 5 trees on the Colorado Front Range is an ash tree, and that species is being threatened by a destructive beetle.

The tree canopy shading the Denver metro is thick and green after a rainy spring – and trees can effectively defend themselves against most invaders when they are healthy. But the emerald ash borer continues to spread.

“There’s probably less trees at risk this year because they’ve all had that good moisture, but unfortunately it won’t translate to ash at all with emerald ash borer,” said arborist Michael Sundberg.

Sundberg said the emerald ash borer, or EAB, can kill any ash tree – even the very strong and healthy ones. That’s why even this summer, the beetle has spread.

“The insect doesn’t travel a great distance by itself," he said. "So a lot times, if it makes a jump from city to city, it's on firewood or a cut-down ash tree that gets driven around and dumped somewhere.”

The Colorado State Forest Service has been tracking the beetle on a map since it was first detected in Boulder 10 years ago. This year, there are now confirmed cases in the south metro area near Littleton, and for the first time, the insect has made its way to the Western Slope near Carbondale. 

The emerald ash borer can devastate a landscape. It's estimated there are close to 1.5 million ash trees in the City of Denver alone. The insect has not been confirmed in Denver yet.

“I mean, just thinking about heat-island effect, losing the shade," Sundberg said. "The property value hit of trees going out.” 

He said you don’t often see the tiny beetles themselves, but the exit holes left by their larva make a distinct D-shaped hole in the bark.

It's best to protect Ash before it gets attacked, Sundberg said. A direct root injection done by professionals can deliver a kind of EAB vaccine every other year.

“Then if that bug is going into the tree, it dies trying," he said. "It doesn’t have a successful attack, so that helps slow the spread."

The ash borer treatment can cost more than $150 per tree depending on the size and health of the trunk.

Credit: stock.adobe

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