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Caterpillars chomping Glenwood’s oaks

Donna Gray
Vail, CO Colorado
Kelley Cox/Post IndepedentA linden looper caterpillar inches its way up the branch of a tree near the Roaring Fork River in Glenwood Springs.
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GLENWOOD SPRINGS ” What’s with the brown trees downtown?

Anyone who drives Midland Avenue between 8th and 28th streets in the last week may have seen a dramatic change in the oakbrush that lines both sides of the street. The shiny green leaves on many of the trees are now dead brown and there are fine threads woven in among the branches.

The critter behind the stripping of the oakbrush on the west side of town is the linden looper, a caterpillar that is attacking trees with a vengeance this year. The caterpillars were also responsible for an infestation of oakbrush in Rulison last year.



The good news is, “they’re usually short-lived,” said Pat McCarty, Colorado State University Extension Agent for Garfield County.

As caterpillars, or larvae, they can attack and defoliate trees and shrubs for one to three weeks in the spring. Then they will fall off the trees and go into their pupa phase after burrowing underground. In the fall they’ll emerge as moths.

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The caterpillar is primarily associated with hardwood trees in the Midwest. “

Why we have it here I don’t know,” McCarty said.

Unlike many species of caterpillar that feed on specific plants, the linden looper doesn’t discriminate. “It’s very devastating to everything above the ground,” he said.



In this area, McCarty said he’s seen them go after oakbrush and serviceberry.

In this first year of infestation, the oak brush should bounce back and regrow leaves. But if the trees get hit a second or third year, it can kill them, McCarty said.

How many years they’ll be around is anybody’s guess.

“They do blow up occasionally and can last several years,” said CSU extension entomologist Bob Hammond. The longer the caterpillars stay around the more damage they do.

“There seem to be more of them this year,” he said.

He suggested if people see the caterpillars on the same trees a second year, they should spray. He recommends spraying Bacillus thuringiensis, a bacterium that kills the caterpillar but does not affect humans or pets.

There are other options. Ed Berkheimer, owner of Earthwise Horticultural in Glenwood Springs, which offers insect and disease diagnosis and treatment for trees, said two chemical insecticides are also effective. Pyrethroid spray is a synthetic insecticide based on the pyrethrum daisy. Neem is a botanical spray extracted from the neem tree. Both are effective on caterpillars.


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