In managing utility forest vegetation, it’s important to understand the various threats to the plants. One of the most intense over the past two decades has been the emerald ash borer. As of 2020, it had affected more than half of the U.S. and Canada. Virtually any location with ash trees has either lost most of the population already or will soon face this ongoing threat.
 

What is the Emerald Ash Borer?

The emerald ash borer, often abbreviated EAB, is an exotic beetle that was unknown in North America before June 2002. Its Latin name is Agrilus planipennis and it is native to northeast Asia. The metallic green beetle is about half an inch long, but its larvae does the damage.

The beetle lays its eggs on the bark of the tree, starting at the crown. When the eggs hatch, the larvae burrow into the tree and feed on the inner bark and cambium. It leaves long, winding grooves under the bark, essentially detaching the bark from the tree and depriving it of nutrients. Eventually, it carves out a chamber in the inner bark where it pupates, emerging through the bark as an adult in the spring. The adults then fly to the next tree, restarting the cycle. Ash trees in its native Asia have evolved to resist the attack.

A tree housing EAB larvae typically dies in two to four years. The invasive pest feeds on all ash species: black, green, white, pumpkin, and blue. They appear to prefer larger trees and trees that are already stressed or weakened.
 

Where Did the Emerald Ash Borer Come From?

The EAB was first seen in southeastern Michigan near Detroit in the summer of 2002, although it’s unknown exactly when it arrived. It is presumed that it traveled to this continent on imported wood. Initially, Michigan, Ohio and Indiana suffered the consequences and hoped to limit the spread. Ash trees were proactively removed ahead of infestation to cut off the beetle’s ability to move to new trees. Unfortunately, it managed to spread beyond those three states by 2009.

Since then, the spread has continued and the EAB is expected to eventually destroy all ash trees in North America. The focus of vegetation management companies and government bodies is on managing and treating individual trees.
 

What Has Been Done to Stop the EAB?

Some work has been done with “trap trees” used to lure the pests to one location and eradicate them with pesticides. Another tack was to attract woodpeckers, which eat the EAB. No method has been able to eradicate the pest. Once they have started to feed on a tree, it is too late to save it.

The USDA has set up quarantines to limit the movement of ash wood from one place to another, especially across state lines. Public awareness campaigns have taken place to prevent the movement of firewood and to learn the signs of an EAB infestation.
 

How Has the Emerald Ash Borer Affected Utility Forests?

U.S. flora has experienced widespread destruction by pests in the past, but there is more critical infrastructure to protect today than ever before. Utility companies across the eastern half of the U.S. and Canada have had to adjust their strategies and budgets to address the threat of the emerald ash borer.

Damaged ash trees can lose limbs, typically within two years of infestation. They eventually lose structural integrity at the base and fall. Failure of limbs or entire trees can happen at any time, in any weather — it is not dependent on storms or seasons, as with other patterns related to managing a utility forest.

Dead or damaged ash trees pose three main types of threat:
 

•     Dropping branches on lines or equipment
•     Falling on lines or equipment
•     Harming the public or utility workers

In addition, working on these trees poses special threats to arborists, since unstable trees are unsafe to climb. They may require specialized equipment to access and remove the trees without climbing them.

Utility companies work with vegetation management experts to proactively remove or top trees before they fail. A certified arborist can identify and mark ash trees, dead or alive, within striking distance of power lines. Coordination must take place with property owners as well, to handle trees on private property and easements. Many utility companies have launched public information campaigns to educate their customers and earn their cooperation. Many seek to proactively inform their customers about the potential hazards caused by ash trees on their property.

While the EAB problem has been a challenge for budgets, the cost of preparation and prevention can outweigh the cost of a problem.