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After drought, bark beetles killing Denver trees

Bark beetles are killing pine trees in the Denver area following the 2021 drought.

CHERRY HILLS VILLAGE, Colo. — A homeowner in Cherry Hills Village noticed that his 90-foot spruce tree wasn't looking so good this spring. By August, the tree was almost completely dead.

Denver Commercial Property Services (DCPS) told him that insects had killed it and the tree should be removed to slow the lifecycle of the bugs.

"It's called an Ips Engraver -- a type of pine beetle," said Tony Hahn, arborist with DCPS. “It’s just hundreds and thousands of these little bark beetles that go after these trees.” 

Hahn said there is a major outbreak happening in the Denver metro area, and one of the worst-hit areas is near Cherry Hills Village. The beetles are mostly attacking spruce and Austrian pine trees. 

“One of the biggest reasons for this is the hot, dry, stressful weather,” he said. 

Hahn said when a tree gets weakened by drought stress, the beetles can actually smell it. 

“The chemical signal from the tree, the insects recognize it and whamo, they all just go,” he said. "By the time you notice there's something wrong with your tree, it's usually too late to save it."

It has been hot this summer in Denver, but at least there’s been some rain to go with it. Hahn said these trees were damaged by last year's drough, the warmest and driest last six months of a year in history. 

“It's fascinating how it takes trees several months to respond to a negative stress," he said. "And that’s what we are seeing.”  

He said bringing infested trees down can help slow the spread, but this outbreak in Denver could last for more than a year. 

“Some insects have just one generation a year, these guys have it all figured out. They have multiple generations," said Hahn. "And as long as the weather’s right, they just keep going.” 

He said that it's important to keep watering trees through the fall months because the tree roots of many species will have a growth spurt during the fall.

And it's best to use a device that gets water all the way down to the roots underground.  

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