Even if you haven’t heard of Emerald Ash Borer before, it will soon be something you can’t ignore.

With as many as a quarter of our urban trees consisting of ash, the potential for losing a significant portion of our urban forest is very real. The Emerald Ash Borer is the most destructive tree insect we have ever seen.


Ash Tree Identification

Leaves are compound; meaning they usually have 5 to 9 leaflets on each stem. Leaves can be confused with walnut, tree of heaven, and hickory, but those trees are far less common around Fort Collins than ash.


White Ash Young white ash trees can have either diamond shaped bark or smoother bark with plates and cracks as in this photo. As the tree matures the trunk takes on the diamond-shaped bark. The color of the bark varies; it can be white, grey, and pink or orange. Autumn Purple ash are a type of white ash and have smooth-barked limbs.


Green Ash tend to have oblong diamond shapes in the bark, and bark tends to be ash grey in color.


Emerald Ash Borer Identification

Epicormic Growth are shoots coming up from low on the trunk and are one indication of Emerald Ash Borer damage.


Woodpecker activity is high in trees with a high population of EAB larvae.

Adult Beetles are only about a half inch long, shiny metallic green and may be found in early summer feeding on ash foliage. (pictured)


Bronze Birch Borer is a close relative of Emerald Ash Borer and exists in the Fort Collins area, and could easily be mistaken for EAB. Probably only an entomologist could tell the difference.

EAB Exit Holes can be found in the trunk and branches of an infested tree. They start higher in the canopy and only show up lower down as the infestation progresses. Holes are shaped like a capital letter D and are quite small.


EAB Background Information

Emerald Ash Borer is an invasive pest that originates from China and other parts of Asia. It probably hitched a ride to the States in packaging material used in shipping. It was first discovered in Michigan in 2002, and has since spread like wildfire. Adult beetles have been observed to fly a half a mile in their lifetime, however, people have helped it spread much faster by moving firewood and through transporting nursery trees.

In Colorado Emerald Ash Borer was first discovered in Boulder on September 27th, 2013 and a quarantine area was established around Boulder County. It is assumed to have been present for several years before first detection.

By 2019 it had escaped the Boulder quarantine and was confirmed in Broomfield, Adams and Larimer Counties.

In December 2019 the State of Colorado removed the quarantine around Boulder County, allowing infested ash wood to be freely transported within the state. The purpose of the quarantine was to slow the spread of EAB to allow governments and citizens time to prepare.

A federal quarantine is still in place, prohibiting ash trees and wood from leaving Colorado.

EAB Damage and Lifecycle

Life Cycle: Adults emerge in May and June and begin feeding on the foliage of ash trees. Females soon begin laying eggs on the bark of ash trees, and the eggs hatch a couple weeks later. Larvae bore into the tree (they are very small so we don’t see these holes) and begin feeding on the nutrient-rich tissue just beneath the bark. The larvae “molt” several times before overwintering in the wood and finish developing in the spring. As the flat-headed larvae chews it’s way out of the tree, it leaves its characteristic D shaped exit hole. At this point the larvae pupates and the adult beetle is formed.


Ash Trees in North America have no resistance to EAB, and so long as the insect’s population is sufficient, all untreated ash trees within an infestation area will eventually die. The process actually takes many years, as many as eight, but visually most of the damage takes place in about two years.

The First Year or two of infestation, the tree may have little or no outside visual symptoms. As things progress, you may notice the canopy of the tree will start to thin. Once the canopy has died back by 40%, treatments are no longer effective, and the tree will likely die within the next year or so. When a tree is heavily infested, there are many other signs as well: Heavy woodpecker activity, suckers growing at the base of the tree, and bark splitting vertically.

Planning Ahead for Emerald Ash Borer

Now is the time to make your EAB management plan.

Failing to plan is planning to fail

EAB is coming, if it's not already here, and it will eventually kill every untreated ash tree in the Fort Collins and Loveland area. The time to have a strategy in place is now, before it's too late. Homeowners and property managers have two options: treat or remove. Doing nothing means having hazardous dead trees standing.


Remove and Replace

One option is to plan to remove the tree, and replace it with a non-ash tree. This makes sense especially for young ash trees that don't yet offer all of the irreplaceable benefits that a mature tree does. It might hurt to consider replacing trees that were only planted a few years ago and are just now getting established but you will probably be better off; treating for EAB is a big commitment.

If this is what you decide to do- NOW  is the time to remove the tree. Waiting for it to die from EAB could be a mistake as at that point you will likely be on a multi-year waiting list to have the tree removed and the stump ground out, and removing a (large) dead ash tree costs more than removing a live one. Also, the sooner you remove the tree the sooner you can get started on growing a new tree.

Emerald Ash Borer in Northern Colorado is inevitable, and it will kill your tree if it is untreated (Only exception I can think of is maybe if you are on an acreage far outside of the metropolitan area EAB may not make it out to your property).

Preventative Treatment

The other option is to consider protecting your tree against Emerald Ash Borer.

There are a few treatment options available. The most powerful is a trunk injection treatment that should be done by an arborist (you can request to get a quote from ArboRx). There is also a soil-applied treatment available to the homeowner but it's not as effective.

Treating a tree or two is generally affordable but it's a long term commitment- perhaps 20 years or more. Treating more than a few trees can get expensive.