4.30.19



Emerald Ash Borer.. to Treat or Not to Treat?







You may have heard of the latest scourge on Denver, and no it’s not just hipsters moving in from out of town this time. It’s worse. The threat is Agrilus planipennis, or more commonly known as Emerald Ash Borer (EAB) and it is quickly becoming one of the most destructive invasive pests of North America. As the name implies, this green beetle targets all varieties of ash trees. In the Denver area alone, about 1 of 6 trees are Ash. Infected trees are killed within 1-3 years of the first sign of EAB symptoms. This many Ash trees dying would be a dramatic loss for an urban forest like Denver.


We know all of this because it’s already happened elsewhere. Michigan, Ohio, Indiana, Illinois and other states have lost millions of ash trees. Right now, Colorado is the furthest West of the Mississippi to have detected EAB. In a way we are fortunate that it seems to be isolated, giving us an opportunity to wipe the population out or at least knock it down before it continues to spread, provided we all do our part. Since Ash is not native to Colorado, there are no natural Ash forests for the beetle to migrate into once it finds no suitable home in treated trees here, thus allowing it to move far away or die out.


These green beetles cause the most damage during their life stage as larvae feeding underneath the bark. As they feed, they restrict the normal flow of water and nutrient uptake by tunneling through the cambium, thus choking out the tree until it dies. Studies on the efficacy of many types of pesticides have been conducted , and based on the data we recommend two. A low invasive trunk spray and a trunk injection. Both applications operate systemically but vary in price.The trunk spray protects the entire tree for a year and the trunk injection has been found to be effective for roughly 2 years. For additional information on what may be best for you, contact us!








Ash trees are a beautiful and important resource that may even add value to your home or business property. Beyond that, they provide shade and are overall nice to look at. In most cases, investing in the treatment options mentioned above can help protect your Ash trees to keep them healthy for years to come. The alternative and more costly option is removal, which may become inevitable if the Ash tree becomes heavily infested with EAB. Every situation is unique and in some cases removing the smallest and weakest tree can be more cost effective than treating every single tree.


As with any tree related pest or disease, contact your local Arborist for more information and/or for an estimate on treatment. Always make sure you’re dealing with a reputable company, licensed in pesticide application by the Department of Agriculture.

Now that we’ve piqued your interest in the Emerald Ash Borer, here are some great resources to help you do your own research so you can make an informed decision on how to protect or treat your Ash Trees:


CO Dept of Agriculture EAB Decision Guide

CO State Forest Service Quick Guide to EAB

Denver's Be A Smart Ash Campaign