Signs of Emerald Ash Borer (EAB)

One in six trees in Denver are ash trees and, if we do nothing, it’s just a matter of time before they’ll ALL be devoured by the emerald ash borer (EAB). 

EAB feasts only on ash trees (Genus Fraxinus), including the green and white varieties which are most common in the City and County of Denver.

How to identify an ash tree:

Diamond-pattern Bark

While this identification method may not be as helpful when it comes to young ash trees (they typically have smoother bark), the bark on more mature ash trees tends to have distinct diamond patterns.

Compound Leaves

A simple leaf is defined as a single leaf that has a bud at the base of the leaf stem. Conversely, a compound leaf (the sort you’re looking for on an ash tree) is defined as having more than one leaflet per leaf connecting to a stem that has a bud at its base. Ash tree leaves typically have 5-9 leaflets per leaf. This photo is showing one ash leaf, with 7 leaflets.

Opposite Branching

By opposite branching, we mean the branches protruding from tree limbs have a mate protruding from the exact opposite side of the same limb. Only ash, maple, dogwood and horse chestnut trees have opposite branching.

How to tell if an ash tree is infested with EAB:

There are several signs to be aware of. S-shaped tunnels can be seen on the trunk under the bark layer and tiny, D-shaped exit holes are often visible in the bark. Additionally, impacted trees show signs of thinning and bark shedding. Dying ash trees also attract Northern Flickers, a type of large, brown woodpecker. The tree takes time to show signs of stress and often dieback begins towards the top of the tree, so it can take 2-4 years for trees to show any signs of infestation.

What does the emerald ash borer look like:

It’s small enough to fit on a penny, so you are unlikely to get a chance to examine one individually. If you do, the adult EAB is identifiable by its dark, metallic-green color and coppery-red or purple abdomen, which can be seen under its wings.

What should you do if you have an ash tree or discover EAB? Go here for more information.