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Emerald Ash Borer Threatens Trees in East, Not Yet in CO

Adult Emerald Ash Borer

Small insects do a lot of damage to trees and our forests.  We’ve seen what the Mountain Pine Beetle has done.  And it’s moved into the trees in our Front Range communities.


Another insect that keeps our city foresters awake at night is the Emerald Ash Borer.  This critter was imported from China and eastern Asia.  It probably hopped a ride to North America in a crate. 

Emerald Ash Borer was first identified in Michigan.  The theory is the borer was doing damage to Michigan ash trees for eight or twelve years before it was officially identified.  It’s infested over five million trees covering 3,000 square miles.  It’s also been found in Ontario, Canada, Ohio and states along the east coast. 

This half inch long beetle has bright green metallic colored wings.  The adults emerge in June and July to mate and lay eggs.  The eggs hatch into a larvae that chews through the tree bark.  Under the bark the larvae continues eating and creating tunnels.  The tunnels cut off the flow of water and nutrients to the tree branches and eventually the whole tree. 

The insect is hard to detect because the damage occurs slowly over time.  Usually the top of an ash tree looks wilted and stressed.  The next season there are some dead branches.  Over three or four years the tree declines and dies.  This critter goes after young and mature ash trees, stressed and healthy trees.

After over-wintering under the bark a new adult emerges the following summer to start the cycle over again.  The Emerald Ash Borer has no North American predators.  Recently some chemical sprays have been effective in stopping the borer. 

Emerald Ash Borer usually stays close to the tree where it was born.  It only flies about one half of a mile.  But it has spread miles over multiple states.  Just as it came into North America, Emerald Ash Borer is being spread by people.  It hitches a ride on pallets, nursery stock, wood chips and firewood.

The Colorado Ag Department is active in stopping the Emerald Ash Borer from entering the state.  So far there isn’t a sign of infestation here.  All nurseries are inspected regularly.  Traps are set throughout the state to capture the insect.  Only a few insects have been captured and those areas are being monitored. 

We can help.  Don’t bring wood products from out of state.  The most mobile wood product is firewood.  Don’t buy or bring firewood home from out of state.


Tom has been offering garden advice on KUNC for almost two decades. During that time he has been the wholesale sales manager at Ft. Collins Nursery, Inc. Since January of 2005 he has been the owner and operator of Throgmorton Plant Management, LLC., a landscape installation and maintenance company as well as a horticultural consulting firm. He lives in northern Ft. Collins with his wife and two kids.