Emerald ash borer detected in Larimer County

The Colorado State Forest Service announced Oct. 2 that national and state experts have confirmed the presence of emerald ash borer (EAB) in Larimer County. Detection of the invasive, highly destructive tree pest near the town of Berthoud represents the first ever in the county, and the third confirmation of EAB in Colorado in less than two months outside the existing quarantine area.

An estimated 15 percent or more of all urban and community trees in Colorado are ash species susceptible to being killed by EAB – and a majority of these trees are on private land. EAB attacks and kills both stressed and healthy ash trees and is so aggressive that trees typically die within two to four years after becoming infested.

The infested ash was located on private property in unincorporated Larimer County, less than three miles southwest of Berthoud. Foresters are now in the process of conducting field inspections of ash trees on other properties in the vicinity, to determine the extent of observable EAB infestation.


Visit the Colorado State Forest Service’s “Green Menace” page to learn more about the insect, forest service efforts to manage the spread of EAB in the state and how to identify ash trees.

Colorado State University Extension’s website has a number of resources on emerald ash borer, including how to determine if your tree has EAB, identification of insects and ash tree management zones.

It is unknown whether this pest arrived in Larimer County by natural spread or via accidental human transport, such as in firewood or other raw ash material.

a chunk of wood from a tree affected by emerald ash borer
A piece of wood affected by emerald ash borer. Photo: City of Loveland

EAB was first confirmed in Colorado in 2013, in the city of Boulder. Since then, the pest has been confirmed in several other municipalities in Boulder County within the quarantine, as well as in Broomfield in late August, and Westminster in September. Experts have now detected EAB in four Colorado counties – all along the northern Front Range.

Staff with Larimer County and the City of Loveland recently helped to obtain insect samples gathered near Berthoud, after an arborist brought an ash log containing the insects to the Loveland recycling center. A Colorado State University Extension agent delivered the insects to an EAB expert on campus, who first confirmed it as being the pest; it was then confirmed a second time by a national EAB expert in Brighton, Michigan.

Quarantine to expire

This detection, like the other most recent Colorado detections in Broomfield and Westminster, occurred outside the existing EAB quarantine area, which primarily encompasses Boulder County. The quarantine was established six years ago in an effort to prevent or slow the insect’s spread via the movement of ash nursery stock, firewood and other wood that may contain the pest.

The Colorado Department of Agriculture and USDA Animal and Plant Health Inspection Service are now preparing to repeal the quarantine at the end of the year, with a formal process beginning last month, because the pest can move to new areas naturally, without transportation of infested wood.

CDA is removing the quarantine to allow affected communities more options for the disposal of removed trees, and because other means are now in place to help slow the spread of EAB in Colorado. These include the presence of chemically treated trees in affected communities, and biocontrols that prey on EAB now having established populations in Boulder.

General public information about EAB is available at csfs.colostate.edu/emerald-ash-borer. Larimer County residents with questions specific to EAB management on their property can also contact their local municipal forester; those outside a municipality with a forestry department can contact the county, CSU Extension or the Colorado State Forest Service:

  • Berthoud Parks and Recreation: (970) 532-1600, org/departments/parks-recreation/forestry
  • Fort Collins City Forester: (970) 221-6361
  • Loveland Parks Forestry Specialist: (970) 962-3459
  • Windsor Forestry Division: (970) 674-2440
  • Larimer County Forestry: (970) 498-5765
  • CSU Extension, Larimer County: (970) 498-6000
  • Fort Collins Field Office, Colorado State Forest Service: (970) 491-8348