‘Aggressive’ bark beetle likely already in Aspen

The Emerald Ash Borer, an invasive species of bark beetle that was discovered in Colorado in 2013 and has been expanding through the state, has the potential to damage the Colorado landscape. 

And Aspen, despite having a lower number of ash trees than other urban settings, isn’t out of the woods.

“In terms of the spread of EAB into the Aspen area, it’s not an ‘if,’ it is a ‘when,'” said Carrie Tomlinson, Urban and Community Forestry manager for Colorado State Forest Service. “That is the case for most places in Colorado. We’ve gotten at least six different communities in the last six months that are new to EAB.”  

EAB presence was detected in Carbondale in June 2023, the first time EAB was confirmed to have spread to western Colorado from the Front Range. In a CSFS press release at the time, CSFS wrote that EAB “is so aggressive that trees typically die within two to four years after becoming infested.”

While only about 3-4% of the city of Aspen’s trees are ash, according to City Forester David Coon, he and Tomlinson stressed that preparation with those trees is still key. The city of Aspen just deployed three EAB traps in public ash trees around town last month that can help detect the beetles early on. Homeowners who have ash trees on their properties should also start keeping an eye out now.

“If you can get ahead of it and think about your plan for managing your ash in your yard, then you can be prepared for it,” Tomlinson said.

Coon echoed Tomlinson’s sentiment.

“At this point, the city of Aspen’s phase of being prepared for EAB has to do with monitoring and spreading awareness about what tree owners can do to look for signs,” Coon said. 

The CSFS website confirms signs of EAB presence include gradual canopy thinning, early fall color, miniaturized leaves that appear smaller than normal, bark splits, increased woodpecker activity, ⅛ D-shaped exit holes in bark, among other symptoms.  

One of the primary mechanisms of spread is firewood, according to Tomlinson.

“The big thing is not moving firewood that is ash, even if the tree has been down for a while and it’s bone-dead dry,” Tomlinson said. “Moving that with bark intact is going to spread EAB, even if it’s chopped up. If it has its bark on it and it’s ash, you should not move it for firewood.”

While ash trees are not native to Colorado, they saw a boom in planting following the loss of a majority of elm trees in the state. Tomlinson said that in the 1950s and 1960s through the 1980s, Dutch elm disease wiped out a “very large percentage” of elm tree populations.

“As a result of that, people started planting ash as a replacement,” Tomlinson said. “But we didn’t quite learn our lesson in terms of managing for diversity, so we set ourselves up for EAB.”

Those who recognize any signs of EAB can get trees treated by a certified specialist with Emamectin Benzoate, a systemic insecticide, Tomlinson said. 

The city of Aspen is licensed in the state to treat its own trees, according to Coon — he also confirmed there is “very little risk” to people, pets, and wildlife when injecting this pesticide into the tree.

Treatment can also be used on healthy trees as a preventative measure, Tomlinson said. She also encourages tree owners to treat before removing their ash trees, which can be a huge cost saver in the long run.

Those looking to treat trees can call Coon at 970-429-2031.