Emerald Ash Borer

About the Emerald Ash Borer Pest

EAB or Emerald Ash Borer is an insect that only feeds on Ash trees (Fraxinus). The most destructive is at the larvae stage, feeding on the sugars within a tree and eventually killing the tree. This insect has wreaked havoc on millions of ash trees in North America and Canada. It is estimated that more than 53 million native ash trees have been killed by the year 2007 (Ecological Economics, Kovacs). EAB was first found in the United States in the 1990s, originally thought to be from ash wood pallets or packing material from Asia. EAB was first discovered in Boulder, Colorado in 2013. Since then, it has spread to Longmont, Lafayette, Lyons Superior, Broomfield, Westminster, Erie (2021), Arvada, and Thornton (2022). Below is a great resource page from the Colorado State Forest Service and that is being continually updated.  

Colorado State University resource on the Emerald Ash Borer

Why should you care?  

The Denver metro area has approximately 1.45 million ash trees, these trees provide an estimated $82 million annual services including stormwater mitigation, energy savings and increased property values. In the City of Lone Tree, there are an estimated 5400 ash trees, which make up 12% of the urban canopy. If all these trees were to die off there could be the same catastrophic impact on neighborhoods that Dutch Elm disease did starting in the 1930’s. Streets that were once lined with beautiful canopies and nice shaded landscapes wiped out. With the lack of mature canopy this leads to increasing surface temperatures, higher energy bills, more stormwater runoff, and increased pollution.  

What can I do now? 

The first step is to know if you have an ash tree on your property. How do you know if you have an ash tree? The key attributes to ash trees are compound leaves with 5 to 9 leaflets. Buds, branches, and leaflets grow directly opposite of each other. The bark also has diamond shaped bark ridges in mature trees. Below is a link helping with Ash tree identification.  

Colorado State University: How to Identify Ash Trees

The next step is to decide what to do, there are four options:  

1. Do nothing.
2. Removal of your tree, make sure to also remove the entire stump. Trees will have stored energy and start to sucker once cut. Suckers can harbor the beetle, and this will lead to more infected trees in the City.  
3. Chemical treatment. Treatment can be costly; it is around $9.00 – $13.00 per diameter. So, if you have a 10-inch diameter tree it will cost around $90.00 every 1-3 years depending on the rate used. Trees that should be treated should be large mature trees that are in good health and have a minimum of 8 inches in trunk diameter.  
4. Shadow planting: shadow planting is planting a tree near the location of the ash tree or on another location of your property. 

What to do if you think you find EAB 

If you believe you have EAB on your property a sample of larvae or beetle will need to be collected. This can be reported to the Colorado Department of Agriculture or Douglas County CSU Extension office. Don’t move firewood! Movement of firewood can spread the insect faster than it can fly, if the beetle is found infected wood needs to be burned within that year or double chipped.  

Beetle ID 

The beetle is a metallic green color and is half an inch in length. Adults are active from May through July while feeding on leaves as they lay eggs on the bark. Once the eggs have hatched the larvae tunnel into the bark to feed on the outer sapwood producing galleries that girdle and ultimately kill the tree. You can peel back the bark exposing the “S” shaped galleries and the exit wounds on the tree are “D” shaped from the adults emerging. There are other boring insects that can appear to be EAB, one such insect is the lilac borer that has more “O” shaped exit holes. For more information, check out this list of resources on the EAB reach out to City of Lone Tree City Forester Sam Waggener to go over options or next steps.