Your Questions Answered: What’s the threat of the Emerald Ash Borer in metro Denver?

The Emerald Ash Borer is an invasive insect that is responsible for the death or decline of tens of millions of ash trees in 21 states. (Photo:

The Emerald Ash Borer is an invasive insect that is responsible for the death or decline of tens of millions of ash trees in 21 states. (Photo:

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BOULDER COUNTY, Colo. — An insect known as the Emerald Ash Borer, which has devastated ash trees across the Midwest, has now triggered a quarantine in Boulder County.

But as experts work to keep it from spreading, homeowners are getting conflicting advice about protecting their trees.

The potential destruction that the Emerald Ash Borer could do to Colorado’s metro areas is huge.

There are nearly 100,000 ash trees in Boulder alone, and in the Denver area the number jumps to 1.45 million. Roughly 15 percent of all the urban trees in the state are ash.

“Our customers, obviously, are very concerned and are calling us for assistance,” said Steven Geist, plant pathologist for Swingle Lawn, Tree and Landscape Care.

For land owners who want to protect their ash trees at all costs, Geist says they recommend insecticide trunk injections if they live within 10-15 miles of the detection site in Boulder.

Though the insect is not yet known to be in the Denver area, Geist says they have offered a less-invasive, soil-injected insecticide. He says the treatment is offered as an option, if their customers are very concerned about certain trees.

“It will take a while for the insect to go throughout the entire area, but it’s good insurance to get your trees treated,” Geist said.

But Keith Wood, one of the experts with the Colorado State Forest Service, says landowners outside the quarantine areas shouldn’t panic and probably shouldn’t spend the money to treat their trees yet.

“I can understand the concern, definitely if you have a high value ash tree and it means a lot to your property there needs to be some concern and questions asked,” Wood said. “But we’re not recommending anyone treat their tree in the Denver metro area right now.”

Treating ash trees with insecticides can cost several hundred dollars a year. Regardless of whether you want to invest, experts say you’ll want to wait until spring, when the insecticides are proven to be most effective. By then a state team of experts will have its own treatment guidelines.

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