Serious Pest - Emerald Ash Borer

Please join me in your sympathy and concern for residents in Boulder County battling emerald ash borers (EAB). In the long term this serious pest won't remain in Boulder County. It's not a matter of "if" it is "when" they will reach other areas along the Front Range. 

Photo from City of Lenexa, KS

As serious pests, the harm they are causing to ash trees is devastating, but it is even more than that. Their presence leaves a sense of hopelessness and loss because there is no stopping it. Once infested, EAB can kill an untreated ash tree in 3-5 years. The emerald ash borer spreads easily from tree to tree - they can fly a half mile. They also spread by infested nursery stock, or firewood carried into uninfested areas. Boulder County has a quarantine on moving any ash wood out of quarantined areas.

Emerald ash borers are silent yet deadly to its host - all ash trees in the fraxinus genus. This includes the attractive autumn purple ash tree that causes driver double takes each autumn. It has been planted by many homeowners seeking and finding great satisfaction with brilliant fall red to purple leaf color. Finding replacement trees with equally fine fall color is possible, but it won't be easy saying good bye to these once easy-care trees. Emerald ash borers do not infest mountain ash trees which are in the sorbus genus. 

Emerald ash borer was first found in 2002 in southeastern Michigan and is now in 27 states plus parts of Ontario and Quebec Canada.  It was found in the City of Boulder in September of 2013.  It is considered the most destructive forest pest in North America, causing millions of ash tree death - those numbers will rise as the insect spreads to new areas, states and provinces. Follow the spread of EAB on this timeline.

Adult borers emerge from spring to summer to feed on leaves, mate and lay eggs in crevices and cracks of ash tree trunks. Eggs hatch in about two weeks, then the new larvae tunnel through the bark into the cambial region of the tree - this is the thin layer of cells just inside the trunk that grows wider each year.  The larvae feed on the sugars in the phloem (inner bark) of the tree, and long term the feeding causes the tree to weaken and eventually die. Adults are most active in the heat and sun from mid-day to early evening.  Males live for about a month, females up to two months and lay from 50 to 150 eggs during this time.

Tree damage is most noticeable on the main upper limbs and large branches.  Look for thinning in the crown of the tree and branches with yellow leaves. Sucker growth on limbs and trunks are indicators. Woodpecker activity is another sign of EAB presence, they peck and leave light colored patches of bark as they feed on larvae. The tell-tale D-shaped exit holes on ash trees are more visible proof of an EAB invasion. The outer sapwood of an infested tree (not visible from the outside) will reveal etched larvae galleries or s-shaped tunnels.

EAB infested trees Boulder, CO summer 2014

Tree industry professionals, City and State agencies and universities are doing all they can to educate the public on identifying ash trees, spotting the insect as an adult or damage left by the tunneling larvae. And most important in the education process are the spray or injection options for treating valuable ash trees and planting recommendations for replacing or adding new trees near ash trees. 


Read all about these options at Be a Smart Ash. Denver residents are eligible for free replacement trees in public right-a-ways, click here for more information - apply for a tree.  At only 1/2 inch long and 1/8th inch wide, Emerald ash borers have generated a tremendous amount of time, attention and dollars. 

D-Shaped Exit Hole

The City of Denver and surrounding counties have done an exceptional job in getting ready for the eventual arrival of EAB with monitoring and planning strategies. Click on any of the links below for additional information. 

Be a Smart Ash 

City of Denver Trees and Natural Resources 

Colorado Department of Agriculture 

City of Boulder 

Emerald Ash Borer Information Network