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By Orla O’Callaghan, Colorado Master Gardener and Native Plant Master

The Emerald Ash Borer (hereinafter EAB) is a small beautifully colored emerald green beetle that is native to Asia.  It was first discovered in the U.S. in 2002, in Michigan.  It probably hitched a ride from Asia in infected wooden shipping or packing materials.  Since 2002, it has spread from Michigan to 22 states (as well as two Canadian provinces).  I am sad to inform you that as of September of 2013, the EAB has been in Colorado, having been first discovered in Boulder.  A federal quarantine area was established to try and prevent human spread of EAB from Boulder County and surrounds.  The quarantine zone efforts have slowed the spread of EAB to neighboring communities, giving them more time to plan and protect their urban ash trees.  Within the quarantine zone, later EAB infestations have occurred in Longmont, Lafayette, Lyons and Superior.   Unfortunately as of August 2019, the presence of EAB beetles has been confirmed in Broomfield and Westminster, which are outside the current quarantine zone.    

So why am I so sad that the EAB is in Colorado?  The EAB is a tiny but deadly insect.  It kills all species of ash (Fraxinus spp.) – white, green, black, blue and purple ash and their cultivars. The EAB larvae feed under the bark of ash trees causing S-shaped tunnels.  The tunnels damage the phloem and xylem tissue of the tree, interfering with the movement of water and nutrients within the tree, this is called girdling.   Damaged trees usually die within 2 to 4 years after the first appearance of symptoms.  EAB can infest all ash trees whether they are young (including saplings) or mature, healthy or stressed.  By the time you notice the symptoms of the larvae feeding, it’s often too late to save the tree.  Because EAB is an alien (non-native) insect, our ash trees have little to no natural resistance against their damage, and there are no native predators of EAB.  Emerald Ash Borers are hard to detect, the larvae are under the bark, and the adult beetles are tiny and only active from May through July. 

            So how big is the EAB problem?  It is huge.  After the Dutch elm disease killed so many elm trees in the 1960s, they were often replaced with ash trees.  It is estimated that ash trees makes up 15% or more of urban trees in Colorado, most of which are on private property. EAB infestations will have a great economic impact.  As an example, there are an estimated 1.45 million ash trees in the Denver Metro area.  The estimated costs of removal and replacement of those trees is over 1 billion dollars.  The cost of treating ash trees of high value in Metro Denver is unknown, but could cost as much as 36 million dollars a year for the life of the trees.  This is only part of the economic impacts that EAB infestations can cause.  Trees increase property values and their absence decreases that value, which decreases property taxes.  Trees reduce cooling costs.  Trees attract people and businesses.  With fewer trees to soak up storm waters, EAB infestations may affect urban storm water systems.  If large numbers of ash trees die, it will affect the amount of carbon dioxide being captured by those trees.  Standing dead trees will pose a threat to communities and will create liability issues.  There will be the huge issue of how to safely dispose of the dead ash trees and other infested materials.  EAB can survive in pieces of wood as small as 2”across.

So what should you do about the EAB? 

1. Don’t freak out.

I know that seems difficult given all I have told you thus far.  It is important to remember that EAB only move about a half a mile per year without help from humans.  Hopefully they will take a while to move from the currently infected Colorado cities to Pueblo.  Ongoing research is leading to some effective treatments.  We as individual and as a City-County have time to plan for EAB.  According to Mike Tate, of the City of Pueblo Parks and Recreation, they have inventoried the ash trees in our parks, and found around 700 ash trees.  They have assessed their size and health, to determine if, or when, to start EAB treatment.  Mineral Palace Park has some prized ash trees that he says may be 130 or more years old.  It is a good start to EAB management in Pueblo.

2. Identify whether or not you have any ash trees on your property. 

Ash trees have compound leaves with 5 to 9 leaflets.  The branches, buds and leaflets grow directly opposite of each other.  Mature ash trees have diamond-shaped bark ridges.   If you don’t have any ash trees you should be glad because the EAB feed on and live in only ash trees.

3. If you do have ash trees on your property you should make a plan of action – Now. 

Think about such issues as: Is the ash tree worth saving?  If so, how and when do I protect it?  People who apply EAB pesticide treatments must be licensed by the State as Commercial Pesticide Applicators.  Contact local arborists to determine who is so licensed.  If you determine your ash is not worth saving, decide when to get rid of it and decide what to replace it with.  If you are removing your ashes, you may want to do that before the EAB reaches Pueblo.  It will likely be cheaper and easier, and it gives more time for its replacement to grow.  Remember that it is best to have a diversity of tree species.  Think about planting native trees and shrubs that are suited to our climate.  Obviously, don’t buy or plant any more ash trees on your property. There is a good EAB decision guide on the Colorado State Forest Service website: 

4.  Learn how to Identify EAB.

The adult EAB beetle is very small at only 1/8” to ½” in length.  It has a slim body that is metallic emerald green.  Note that the Japanese beetle is also emerald green, but it’s bigger and has a rounder body shape.  There are also other beetles that are similarly sized and shaped as EAB but they are not emerald green.   

5.  Learn to identify the signs and symptoms of EAB

An ash tree can be infested with EAB for up to four years before visible signs of the infestation occur.  Watch for thinning leaves in the upper canopy of your ash trees, and 1/8” D-shaped emersion holes in the bark.  Look for vertical cracks or splits in the bark with S-shaped tunneling in the wood below.  Note there are other borers, like the lilac-ash borer, that may look like EAB or cause similar signs or symptoms as EAB.  If you have identified the tree and an ash and see signs of EAB infestation, report it to the Colorado Department of Agriculture at 1-888-248-5535.  If you are not sure, the extension office can help answer your questions.

6. Don’t spread EAB by moving infested firewood! 

EAB can travel farther faster, with the unwitting aid of humans.  You should never carry firewood or wooden packing materials, including palettes, outside of, or into the state, or from the EAB affected areas.  Buy firewood in the area where you are going to burn it, and don’t transport it outside that area. The EAB probably arrived in Colorado in infested firewood.  Pueblo may be at higher risk of EAB being introduced in firewood.  Lessons learned from other states with EAB, is that infected firewood is sometimes transported in horse or livestock trailers.  Given that we host the State Fair, we may be at a higher risk than other communities to have EAB introduced from firewood.   Do your part and don’t spread EAB. Stay informed of the spread of EAB in the state. 

I hope that now that you know about EAB, you will help look out for it.  The sooner we detect EAB, the better we can respond to safe our ash trees.

For more information about EAB, check out the Colorado State Forest Service website above.  It has excellent photos to help you identify ash trees, the EAB and the symptoms of EAB infestation. 

Sources: Colorado State Extension ( and the Colorado State Forest Service website (listed above).