Invasive insect noticed on local aspens |

Invasive insect noticed on local aspens

Lauren Glendenning
Vail CO Colorado

EAGLE COUNTY, Colorado – The mountain pine beetle isn’t the only insect infecting local trees – there’s an insect that takes a liking to aspen trees, too, and it can be deadly.

While the insect, known as the aspen scale, has nowhere near the far reaching devastation to aspen trees that the pine beetle has had to lodgepole pines, the tiny bug is still concerning.

Edwards resident Raymond Bleesz noticed something odd affecting the barks of the aspen trees in his yard this summer and began to research what he was looking at. The trees look sickly, he said, so he contacted the Colorado State University Extension office in Eagle.

“I’ve lived here since 1990 and I have over 40 aspens on my lot,” Bleesz said. “Over the years, I’ve never seen anything like this. It’s not pleasant to see or touch.”

Bleesz brought samples of the sickly trees to a master gardener at the Eagle extension office, who then got in touch with Bob Hammon, an extension agent in Grand Junction who has done extensive research on aspen scale.

Hammon has researched the insect in Aspen and in Vail and said it’s an urban insect, meaning it’s not going out into the native stands in the forest, but rather staying in and around mountain towns. He said the problem appears to be more severe in Aspen.

It attacks a tree’s trunk, and just because one aspen tree in a stand has the insect, it does not mean others in the stand will necessarily suffer.

“It’s on street-side trees, landscaped trees, not on forest trees,” Hammon said. “And on trees that are under stress.”

The aspen scale is a little, round insect that kills trees that are under stress, Hammon said. It doesn’t look like an insect at all to the naked eye, and it’s also very difficult to control.

“Keep your trees healthy is the best way to prevent it,” Hammon said.

There are some ways to control the insect with insecticides, but timing is critical, he said.

The scale has a round, hard covering, like a shell. The tree itself will look like it’s generally unhealthy, but the scale itself is limited to the bark of the tree.

When scale eggs hatch into a mobile form, called a crawler, they move and then settle down and create that hard covering. Once it settles, it doesn’t move again for the rest of its life.

“You have to target the crawler stage to treat it, which is at the end of June and early July,” Hammon said. “Timing is critical for control. … Scale insects have a pretty relatively complex life cycle.”

While the insect can kill weaker trees, healthier trees can recover from an infestation if it’s caught and controlled at the right time, Hammon said.

Bleesz is concerned it could spread to more trees in Eagle County. He said of the 40 or so aspens on his property, there are at least three trees that have aspen scale.

“I have not run into anybody as of yet who has it in their immediate yard around me,” Bleesz said.

Community Editor Lauren Glendenning can be reached at 970-748-2983 or

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