Emerald Ash Borer

Earlier this fall, Colorado Department of Agriculture confirmed the first sighting of an Emerald Ash Borer in Colorado.  This is the farthest west that this extremely destructive invasive pest has traveled. As we wait for more information from the state, there are some things homeowners should be aware of.  We've compiled this short guide to help you understand more about this invasive species. 

General Info

Emerald Ash Borer Agrilus planipennis is a small, metallic green beetle that is native to Northern China, Korea, Japan and Eastern Russia. Scientists are not sure how the borers came to America, but they were probably mistakenly transported in ash wood used as packing material.

Outside of their natural range, Emerald Ash Borers are extremely invasive and have been destructive to ash tree populations throughout the Midwest. Experts have called it the most destructive forest pest ever seen in the United States. 
Adult Emerald Ash Borers feed on the canopy leaves of ash trees between May and August and generally cause little damage. After a week of feeding, they mate and lay their eggs in the bark of the tree.  After 2-3 weeks, the larvae hatch and immediately start to tunnel into the bark of the tree and begin to feed on the tissue that transports water and nutrients from the tree's roots through the trunk to the crown. As they feed, the larvae create tiny meandering tunnels called galleries. These galleries disrupt the flow of water and nutrients, eventually killing the tree. The larvae feed through October and then go dormant as pupae over the winter. Starting in May they emerge as adults and continue the cycle. 

Symptoms and Signs of Emerald Ash Borer

There are some signs and symptoms that you can be on the lookout for. To report a suspected sighting, contact the Colorado Department of Agriculture at 888-248-5535 or email CAPS.program@state.co.us  

Canopy Die Off - The galleries dug by Emerald Ash Borer larvae disrupt the flow of water and nutrients to the top of the tree. Leaves will start to die in the top third of the tree.

Epicormic Shoots - Sprouts growing from the roots and trunk are the tree's way of compensating for damage to other parts of itself.

Woodpeckers - Many woodpeckers feed on Emerald Ash Borer. An increase in their activity can point to infestation. 

Bark Damage - Bark will split vertically exposing the larvae galleries just beneath.

Galleries - "S" shaped zig-zags that larvae cut while feeding. They run back and forth across the grain of wood. The galleries are also filled with a substance called "frass" which is a mixture of excrement and sawdust.

Exit Holes - Adult Emerald Ash Borers make distinctive "D" shaped exit holes when they emerge. This might be the best method of detection as no other ash borers in Colorado make marks like this. 

To see some pictures of the following symptoms, click here


Controlling insects that feed under the bark of trees is always difficult, but there are some things you can do to protect your trees from this invasive pest.

Tree Care - Although all ash trees are susceptible to the Emerald Ash Borer, they target weak and stressed trees first. Be sure to keep your trees well watered and remove any dead or damaged branches. 

Systemic Insecticides - Systemics have been shown to have some success controlling Emerald Ash Borer. The best systemic available to regular homeowners is imidicloprid, available under the brand name Tree and Shrub. You just mix the concentrate and pour it around the base of the tree. Tree and Shrub gives up to 12 months of protection.   According to the Coalition for Urban Ash Tree Conservation, treatment is most appropriate after infestation has been detected within 15 miles, and is most effective when applied before trees are infested. 

Click Here for a Frequently Asked Questions Dopcument regarding potential side effects of systemic insecticides used to control Emerald Ash Borer.


Transporting raw wood is the main way invasive species travel. As a result, authorities are asking the public to adopt a "Buy it where you burn it" policy to avoid a large scale Emerald Ash Borer infestation. Colorado State University recommends asking these questions before purchase.


Where was this wood cut? - Wood should not be brought in from other states, nor transported from distant cities.Leave any unburned wood at the campsite. Don't pack it home.


Is local wood available for purchase? - Look for Colorado Forest Products logo which means 50% of wood is from Colorado forests.


Is this wood treated - kiln dried or debarked? - Firewood should be dry and ready to burn. Bark should be off easily and be removed before transplanting.


What tree species is this wood? - Ash is high risk because of emerald ash borer.

Additional Info

Colorado Department of Agriculture - Colorado specific Emerald Ash Borer info.


Identifying Ash Trees - An easy guide to recognizing the ash trees in your landscape.


CSU Extension Fact Sheet - Info from Colorado State Extension Office, including native species often mistaken for Emerald Ash Borer.