Emerald Ash Borer Now Confirmed in Larimer County Colorado

The Threat of Emerald Ash Borer in Colorado

Update: Emerald Ash Borer has now been confirmed in Larimer County, just outside of Fort Collins and Berthoud. It has also been found in Boulder, Gunbarrel, Longmont, Lafayette, Lyons, Superior, Broomfield and Westminster. 2019 is the first year the insect was detected outside of the quarantine area.

The Emerald Ash Borer is quickly becoming the country’s most famous invasive pest. The Fish and Wildlife Service estimates that invasive species as a whole cost the United States more than $120 billion annually. This insect has infested Ash trees in more than 20 states. The sense of urgency is here to save the Ash trees of the US against this seemingly unstoppable predator.

emerald ash borer colorado


The Emerald Ash Borer or EAB is a type of beetle that can only grow inside of Ash trees. The beetle has distinct markings such as bright metallic green wings, purple underneath the wings, and a brown torso. The insect is about approximately 2 centimeters long and has a distinct bullet shape with a flat head.

ash borer colorado

How long has Emerald Ash Borer been in Colorado?

The EAB was confirmed in Colorado in September 2013 and as reported July 30, 2014, was noted to be spreading into different areas of Boulder and then Longmont. Boulder county was placed under a federal quarantine. Though now it appears the quarantine was a futile effort. There currently is no method of monitoring the spread of the insect. Colorado State University encourages homeowners to monitor their ash trees and look for telltale signs of the bug’s infestation. The EAB leaves distinct characteristics on the ash tree it is burrowing in.

How did the emerald ash borer get to Colorado?

It is thought that the beetle hitched a ride on firewood brought into the state.

How serious is this problem?

According to the Colorado State Forest Service, approximately 15% of the urban trees in Colorado are Ash. The majority of which are on private land. Here is a map of the known infestations of EAB in Colorado. The Colorado Department of Agriculture says that Boulder has approximately 98,000 Ash trees and the city of Denver has nearly 1.5 million.

When the emerald ash borer is a newly formed larva, it burrows under the layer of bark in the Ash tree. They feed by boring tunnels. These tunnels are easily noticed because the larvae leave them packed with excrement that looks like sawdust also known as frass.

As the EAB larvae grow, they burrow deeper into the tree and chew a hold in which they then turn into the full-grown beetle. Then the beetles chew their way out of the ash wood. When they exit, they leave a distinct ‚ÄúD‚ÄĚ shaped hole. It is important for homeowners to inspect their trees and contact a Fort Collins tree service or the Colorado Department of Agriculture so the tree can be further inspected if any suspicious larvae or bugs are seen on a tree.

Since the infestation begins at the upper canopy level, it is difficult to monitor for early detection except to keep watch for mature adult beetles.

EAB in Colorado

This is not a problem that shows symptoms within a month. The infected tree will not show signs of emerald ash borer infestation for at least 2-3 years. Then the upper canopy will begin to thin with leaves turning colors due to lack of water. Homeowners may soon see an increase in Woodpeckers which are natural predators of the larvae and beetles. As long as the tree is receiving water from the root system, it will still live. But as the larvae spread and cut off the water supply to the tops of the trees, the injection system of eradicating the larvae is too late to save the tree.

Where else is this invasive insect found?

It was first discovered in Michigan in 2002. EAB is a native of Asia and mostly likely came to the United States on pallets or packing material. The infestation of the EAB has increased to 20 states.

But areas just east of Colorado should provide a natural barrier as no Ash trees are found closer to the plains. The city of Boulder is still under federal quarantine. Firewood and lumber are not allowed to leave Boulder County.

In Indianapolis, it is estimated that 30% of the trees in that urban forest areas are Ash. It is also estimated that they will all be dead within 8-12 years.

If the Emerald Ash Borer moves to the East Coast, the devastation could easily intensify and increasingly drastic measures will have to be taken or the urban landscape of many states will be dramatically changed over the next few decades.

Can the Ash trees be saved from EAB?

The spread of emerald ash borer in Colorado is inevitable. In fact, the City of Fort Collins is already practicing sound urban forestry management by removing some city-owned ash trees and replacing them with a variety of different species. The goal is to have a more diverse urban forest to shield against a loss of a large percentage of the tree population due to a pest killing one certain species of tree. The more diverse the urban forest, the less it will be impacted by the loss of a single species.

According to the Colorado State Forest Service, the most important action homeowners all over Colorado can take now is to determine if they have ash trees.

Colorado State University and the Colorado State Forest Service, among others, have teamed up to form the Colorado EAB Response Team to attempt to manage the insect.

But what can be done to protect my Ash tree?

There is an effective EAB treatment that ash tree owners can employ to prevent the their trees from being invaded by this devastating insect.

The treatment I referred to needs to be applied every 2 years for the life of the tree. If a treatment cycle is missed, then the ash tree will be susceptible to EAB invasion and the previous years’ treatments (and money) will be a complete waste.

This is a long-term financial commitment that must be considered carefully. It is not an easy decision as it depends on whether or not the tree is even worth saving. There may be severe structural defects that make the tree unworthy. An arborist can evaluate your trees for good structure.

You have 2 other options:

  1. Remove the tree(s) now and start over with a new variety of tree. See my recommendations here.
  2. Enjoy your ash tree(s) until the beetle kills them and start over then.

When it comes to the Emerald Ash Borer in Colorado, there really isn’t any good news to share. We just have to make the best of the situation. Please share this information with people in your community so that all can be informed.

Image courtesy of emeraldashborer.info