Beetles are killing millions of trees every year in Colorado, but the University of Denver has lost just seven trees in as many years.
Arborist Marc Hathaway says most of the damage in the state is caused by the mountain pine beetle, which attacks lodgepole and other pines. In Denver and the Front Range, the big problem is the ips beetle. One species attacks pine and another of the eight ips beetle species attacks spruce.
Ips beetles killed a pine and six spruce trees on campus, but Hathaway says those trees were already weakened because they were in a construction zone where irrigation had been cut off. And four of those trees died before the University began spraying trees with Astro, an insecticide that kills bark beetles, such as ips.
Twice each year since 2001, the University has preventively sprayed 300 campus pine and spruce trees to protect them from beetle attacks. The treatment costs about $9,000 per year, Hathaway says. The most recent treatment was in mid-March.
“This one is one of the best [treatments] in terms of cost and effectiveness,” Hathaway says.
Although Astro kills “good” insects as well as bad — and the chemical can kill fish if it gets into the water — it’s much safer, Hathaway says, than what was available in the past.
If spraying doesn’t work, Hathaway says a beetle infestation would be obvious.
“With spruce, the top would die. The needles would turn brown and fall out,” he says.
The tiny beetles make pinholes, usually in a weakened limb, and then burrow towards the trunk. They tunnel into the cambium layer — the strawlike vertical pipes that carry water up to the limbs — cut off the water supply and do massive internal damage. Pinhole exit wounds from larvae escaping are telltale signs of a beetle infestation.
By the time a tree starts to turn brown, it’s usually too late to save it.
“As soon as you can, you want to get it out,” Hathaway says, noting that felled trees must be removed from campus immediately.
Hathaway says homeowners should keep a watch for dying branches and either have an International Society of Arboriculture (ISA) certified arborist examine the tree or take a sample to the plant diagnostic clinic at the Jefferson County Cooperative Extension Office to determine if beetles are to blame.
Firewood, too, can harbor beetles. The Colorado State University Extension office recommends storing wood outdoors until needed, stacked so air readily flows through the pile. To avoid infested wood, they say to choose trees that have been dried for at least a year or that have noticeably loose bark. Covering woodpiles with a clear plastic tarp can kill insects.