Emerald Ash Borer – The Scourge of the Ash Tree World – Updates Below!

By Valerie Podmore, CSU Extension – Denver Master Gardener since 2020

With spring fast approaching (can you believe we are already in the middle of February?!), our thoughts are turning to those garden tasks needed to ensure all our plants grow healthy, strong, and beautiful. Unfortunately, that includes the not so fun task of looking for and hopefully pre-empting attacks by pests intent upon killing our ash trees…you know who I’m talking about. The emerald ash borer insect, or EAB for short.

What is EAB?

Emerald Ash Borer Adult by David Capered, Bugwood.org

The emerald ash borer is an insect native to Asia, inadvertently introduced in the US in the 1990’s probably via wooden shipping pallets or packing material. This small but deadly tree predator is a green metallic beetle, the adult being approximately one-half inch long with a metallic green head and back; the abdomen is coppery-purple in color. The larvae are up to one-half inch long, have prominent bell-shaped segments and are creamy-white in color. It lacks predators to keep it in check and is now considered the most destructive tree insect pest ever to be introduced into North America and is known to kill all true ash trees.

It was first detected in Colorado in Boulder County in 2013 and even with a quarantine in place (more on that in a minute), the insect has been confirmed to have spread to Westminster and Broomfield and unincorporated Larimer County near Berthoud in 2019. The most recent confirmed detections have been in Erie (June 2021) and Thornton (June 2022). Since approximately 15% of the Colorado urban area tree population are ash tree species susceptible to being killed by EAB, it’s important to do whatever necessary to prevent this pest from spreading even more.

EAB Quarantine

In this highly informative article from 2017 “Emerald Ash Borer: To Treat or not to Treat”, the plant-pest quarantine manager for the Colorado Department of Agriculture and lead member of the Colorado Emerald Ash Borer Response Team, Laura Pottorff stated: “While we can tell you definitively where EAB is known to be in Colorado, and where treatments of high-value, healthy ash are now necessary, it’s impossible to tell you where EAB isn’t located.”

With these confirmed detections of EAB outside of Boulder County, the Colorado Department of Agriculture lifted the quarantine from that location in December of 2019, removing restrictions on the transportation of firewood and other wood supplies across counties (but don’t go crazy bringing firewood from outside your county…as they say “burn it where you buy it”). As this press release from the Department of Agriculture explains, the quarantine helped by slowing down the spread enough to allow for treatment options and or replacement of trees to occur.

So, what does all this mean for you? Since the eradication of this pest is really going to be impossible as noted in this article by The Colorado Sun, and it takes two to three years for the effects of EAB to be evident on an ash tree, it means we who live along the front range and have trees need to be vigilant and take the steps necessary to protect or replace our ash trees (I know…SAD).

Ash Tree by Gary Fultz, unsplash.com

EAB Tips for Front Range Residents

Take a look at this checklist from the Department of Agriculture:

• Determine now if you have any ash trees. Identifying features of ash trees include compound leaves with 5 to 9 leaflets; leaflets, buds and branches growing directly opposite from one another; and diamond-shaped bark ridges on mature trees. More information about ash tree identification, including a helpful app.
• If you have an ash tree, start planning. Decide if the overall health of the tree and the benefits it provides merit current or future treatment, or if it would be best to remove and replace it with a different species. If you are not sure, contact an ISA Certified Arborist. If you do plan to treat the tree, the Colorado State Forestry Service (CSFS) offers recommendations for selecting a tree-care company.
• Plant trees. Replace ash trees in poor health with diverse species. The Colorado Department of Agriculture (CDA) offers a database of registered nurseries and landscape contractors.
• Recognize signs of EAB infestation. Property owners with ash trees should be on the lookout for thinning of leaves in the upper tree canopy, 1/8-inch D-shaped holes on the bark and vertical bark splitting with winding S-shaped tunnels underneath. Report suspect trees by calling the Colorado Department of Agriculture at 1-888-248-5535 or email CAPS.program@state.co.us.

D shaped holes damage by Daniel Herms, The Ohio State University, Bugwood.org

An additional note from the Colorado State University Extension office is that drought and general urban stress of Colorado’s ash trees may mimic EAB symptoms. If in doubt, contact an arborist to know for sure.

If you want to learn even more (and let me tell you it is VERY possible to spend a good chunk of time reading about this pest!), there are great suggestions on this page from Colorado State Forestry Service, and this resource page from CSU Extension. Finally of course there is the group “Be A Smart Ash” whose website is full of information like this as just a start.

S shaped tunnels damage by Daniel Herms, The Ohio State University, Bugwood.org

While this whole subject can be disheartening, especially as we love trees and want to keep them alive for many years, the reality is that we might lose a beloved ash tree. However, with some planning and proactive care, we also might be able to continue to enjoy the beauty of these trees (or alternates) for many years to come, and who knows, maybe the EAB will experience some sort of insect pandemic that wipes it out! One can dream.