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Emerald Ash Borer

Emerald Ash Borer

Adult emerald ash borer in bark


Boulder is the first location where emerald ash borer (EAB) has been found in Colorado. City of Boulder forestry staff identified an ash tree in northeast Boulder near the intersection of 30th Street and Iris Avenue, on Sept. 23, 2013, suspected of having been killed by EAB, a federally quarantined tree pest. Insects collected from the tree were submitted to the USDA Systematic Entomology Laboratory where the insect’s identity was officially confirmed.

EAB is a federally quarantined, invasive tree pest responsible for the death or decline of more than 50 million ash trees in 22 states since its initial discovery in Michigan in 2002. Since then, the small green metallic colored pest, originally from Asia, has spread from Michigan to 21 states, unfortunately now including Colorado.

EAB will cause a huge impact on the urban tree canopy for the Colorado Front Range. The EAB attacks only ash trees, and all North American ash species – including green, white, black and blue – are at risk. Ash trees, especially green and white ash, are popular shade trees in most Colorado communities.  Ash trees are relatively fast growing and several varieties produce brilliant fall colors. There are an estimated 98,000 total ash trees in Boulder alone; the Denver metro area has estimated 1.45 million ash trees. All susceptible ash trees will die from EAB if not treated with pesticides.

There are approximately 38,000 city park and public street rights-of-way trees under the jurisdiction of Parks and Recreation Urban Forestry; approximately 4,800 are ash trees (12.6% of the public tree population).   The 2013 United States Forest Service Metro Denver Urban Forest Assessment Report estimates there are 616,000 trees total in Boulder with an appraised value of $1.2 billion; there are an estimated 92,000 ash trees on private property within city limits.

Symptoms of EAB

Symptoms of EAB infestation include:

  • A general decline in the health of the ash tree
  • Dead branches
  • Crown thinning
  • Excessive sprouting
  • Serpentine “S”-shaped tunnels under the bark produced by the larvae
  • “D”-shaped adult exit holes on the bark surface
  • Woodpeckers often remove bark from infested trees and feed on the larvae; the damage from woodpeckers can be severe and can often be seen from the ground.

If you live within the city limits of Boulder and think you have EAB in your ash trees, or if you have any questions or concerns, or would like additional information, please contact the City of Boulder Forestry Division at 303-441-4406.

If you live outside the Boulder city limits and think your ash tree has EAB, please contact the Colorado Department of Agriculture at 888-248-5535 or email

Emerald Ash Borer Photos

EAB Adult in barkExcessive sprouting in lower branchesWoodpecker DamageWoodpecker Damage 3D shaped exit holeD shaped exit hole and bark splittingBark SplittingD shaped exit holes 2EAB Larvae and S shaped gallery under barkCrown Dieback in large ash tree

See all related photos in the Photo Gallery


EAB is a federally quarantined tree pest. US Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine (APHIS-PPQ) has jurisdiction over federally quarantined pests and works with state cooperators to detect, control and prevent the human spread of EAB. APHIS-PPQ has jurisdiction over the movement of firewood and other ash wood materials between states while the Colorado Department of Agriculture (CDA) has jurisdiction over movement between counties within Colorado. APHIS The goal of a quarantine is to contain the pest and prevent its spread to other states and Colorado counties.

To prevent the spread within Colorado, the CDA imposed and will enforce a quarantine on the movement of all ash tree products and hardwood firewood out of Boulder County. The quarantine took effect Nov. 12, 2013.  After discussions with the city of Boulder, Boulder County and local trash haulers, CDA also included small portions of Jefferson and Weld counties to include two landfills within the quarantine area to facilitate movement of flood debris and EAB-infested material.

The quarantine prohibits the movement of all untreated plants and plant parts of the genus Fraxinus (all ash trees) out of the quarantined area and includes, but is not limited to:

  • Logs and green lumber
  • Ash nursery stock
  • Chips and mulch, either composted or uncomposted
  • Stumps, roots and branches
  • Firewood of any non-coniferous (hardwood) species

The discovery of emerald ash borer in Boulder makes Colorado the 22nd state where this insect has been detected. In 2013, infestations were also found for the first time in Georgia, New Hampshire and North Carolina. The most current map of the EAB infestation across the United States can be found by clicking on the "EAB Map" link in the gray box.

Detection Survey

Because EAB is very difficult to detect in early stages, a detection survey was conducted to establish the boundaries of the area considered to be infested by EAB. The survey started on Nov. 4, 2013 and was completed on Jan.15, 2014. EAB larvae were found and positively identified in sampled ash trees within five of the grids (E3, F3, G3, H3 and H4), including on the University of Colorado East Campus (see map links on the right). Unfortunately, because EAB is very difficult to detect in early stages and adult beetles can easily fly one half mile or more, it is likely that EAB is present at low levels in other areas within the city of Boulder. Monitoring efforts by City of Boulder Forestry staff in 2014 will focus in those grids adjacent to where EAB was detected in the survey.

For the detection survey, Boulder was divided into plots or grids of one-square mile each.  Crews removed two small branches from each of 10 ash trees near the center of each plot. The branch samples were peeled and examined closely for the presence of emerald ash borer life stages. Any EAB life stages were positively identified by entomology staff at Colorado State University. The survey was conducted cooperatively by staff from the City of Boulder Forestry Division, Colorado Department of Agriculture (CDA), Colorado State University Extension, U.S. Department of Agriculture Animal Plant Health Inspection Service (APHIS), the Colorado State Forest Service, the U.S. Forest Service, University of Colorado and forestry staff from nine Front Range cities. Branch sampling protocols were developed by the Canadian Forest Service (CFS); they found by performing random branch sampling on asymptomatic trees with this technique, they were able to detect EAB several miles away from the original location before trees become symptomatic.

City of Boulder EAB Management Plan

The results from both the updated public ash tree inventory and the delimitation survey will be analyzed and used to develop a City of Boulder EAB Management Plan to manage the infestation within the city and potentially slow the spread to nearby communities. 

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