The emerald ash borer has made its way to Thornton, according to city officials. 

 

Thornton Parks, Golf and Forestry Superintendent Paul Burkholder said experts from Colorado State University Extension positively identified the insect in Park Village Park.

 

This is the first time it’s been found in Thornton.

 

“It's probably been here for so many years,” he said. “Trees don’t show infection until several years prior to the visibile dieback.”

 

According to the Colorado State Forest Service, the emerald ash borer is an insect that has killed tens of milions of ash trees in North America. As a non-native insect, it lacks predators to keep it in check. It is considered the most destructive tree insect ever in Canada and the United States. 

 

The Colorado State Forest Service's website states the emerald ash borer has been confirmed in unincorporated Larimer County and in the cities of Boulder, Gunbarrel, Longmont, Lafayette, Lyons, Superior, Broomfield, Westminster, Erie and Arvada. And now, add Thornton to that list. 

 

The emerald ash borer only infects ash trees, and three in Park Village Park were identified as infected. 

 

Although the emerald ash borer has only been identified in that park, Burkholder suspects it has made its way to other places around Thornton due to the park’s central location. 

 

He said the bug was first found in Boulder in 2013, but Colorado’s municipal forestry departments have been preparing for an infestation for years. The pest was first discovered in the U.S. in Michigan in 2002 and has been detected in Boulder, Gunbarrel, Longmont and Lafayette since 2013.

 

The state forest service began a quarantine around Boulder County in 2013 to help prevent the human-assisted spread of the pest. But the borers broke quarantine four summers ago when pests were found near 136th Avenue and Main Street in Broomfield in August 2018.

State agriculture officials said they didn’t know if it spread there naturally — the insects can spread a half-mile each year on their own — or if it was brought in by people accidentally on firewood or infected ash bark used to decorate yards and gardens.

 

The bugs were found in Westminster in 2019 and Arvada in 2020. Westminster had about 69,000 ash trees in the city limits at the time the infestation was first discovered.

 

Once a tree becomes infected, there is no cure to save it. Thornton began treating ash trees to prevent infection in 2021, which means the emerald ash borer has been in the city for several years, Burkholder said. 

 

By the time the insect can be identified, 30% of dieback has already occurred. It takes between two and five years for the tree to be completely gone. He said it’s impossible to get rid of the insect, and it will affect the tree canopy. 

 

Currently, Thornton manages 1,600 public ash trees. 

 

Emerald ash borers will lay their eggs in the ash trees, and once the larvae hatch, they eat on the inside of the tree bark, cutting off moisture and food supply for the tree. They start in the canopy and make their way down.

 

Property owners with ash trees should be on the lookout for thinning of leaves in the upper tree canopy, 1/8-inch D-shaped holes on the bark and vertical bark splitting with winding S-shaped tunnels underneath. People that find suspicious trees should report them by calling the Colorado Department of Agriculture at 1-888-248-5535 or filling out an EAB Report Form at the department's website.

 

The best treatment is emamectin benzoate, an insecticide that was invented in 2001. For a simple treatment, tree owners can put the poison on the ground around the trees, where it will get absorbed into the trunk of the tree or they can drill into the trunk itself to inject the pesticide.