BERTHOUD, Colo. — Emerald ash borer (EAB) – an invasive, highly destructive tree pest – has been detected near the Town of Berthoud in Larimer County, according to the Colorado State Forest Service.

This detection represents the first ever in the county and the third confirmation of EAB in Colorado outside of a federal quarantine in less than two months.

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

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. 

Emerald Ash Borer in Larimer County tree
A tree in Larimer County infested with Emerald Ash Borer
Nathan Sewolt, A-1 Natural Arbor Care

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 this week by a national EAB expert in Brighton, Mich.

RELATED: First Colorado case of emerald ash borer outside of quarantine confirmed

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. 

This detection, like the other most recent Colorado detections in Broomfield and Westminster, occurred outside the existing EAB quarantine.

 The state quarantine boundaries will not change, however, due to plans for its repeal. The quarantine, which primarily encompasses Boulder County, 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.

RELATED: 2nd Colorado case of emerald ash borer outside of quarantine confirmed

The Colorado Department of Agriculture (CDA) and USDA Animal and Plant Health Inspection Service are now preparing to repeal it at the end of the year, with a formal process beginning last month. The repeal is largely due to the insect’s ability to naturally spread to new areas, without the movement of infested wood being the sole means for population expansion.

CDA is also removing the quarantine to allow already-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.

An estimated 15% 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, a release from the Colorado State Forest Service says.

EAB attacks and kills both stressed and healthy ash trees and is so aggressive that trees typically die two to four years after becoming infested, according to forestry officials.

RELATED: Be a Smart Ash: City of Denver prepares residents to battle destructive emerald ash borer

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. Many Front Range and Larimer County communities have been managing for EAB before its arrival, including Berthoud, Fort Collins, Loveland and Windsor.

Approximately 22% of all public-area and street trees within Berthoud are ash, but there is no current data on the percentage of private property ash in town. 

In preparation for EAB, Berthoud began selectively removing and replacing undesirable ash trees approximately three years ago, in addition to treating highly valuable ash. 

Town staff are advising Berthoud residents to act now; residents should first determine if their property has any ash trees, and if so, evaluate the condition of each tree now and in the upcoming spring. 

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 
  • 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

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