The emerald ash borer (EAB), which feeds on ash trees and is now the most destructive forest pest in U.S. history, has arrived in Colorado, and it’s knocking on Denver’s door. That fact is overwhelming in its own right.

But you might find yourself even more overwhelmed by all the treatment options available to protect your ash tree from EAB. That’s where we come in.

For starters, there are four treatment options that have been examined at length as part of a multi-state insecticide study from Colorado State, Ohio State, Michigan State and Purdue universities: trunk injection, soil drench, bark spray as well as ash tree removal and replacement.

Below is a breakdown of each option, with a little help from our Friendly Neighborhood City Forester and superhero, The Smart Ash — who just so happens to be the spitting image of our Denver City Forester, Rob Davis.

EAB Treatment Option: Trunk Injection
  • Who applies treatment: Licensed pesticide applicators
  • Treatment process: A licensed pesticide applicator will drill through the bark and into the outer sapwood of the ash tree, where they will inject the insecticide
  • Frequency: 1-3 years, depending on selected product
  • Effectiveness: When properly administered by a licensed tree care professional, some trunk injections have shown to be 90 percent effective at controlling EAB, making this treatment the most effective method by far
  • Drawbacks: Cost and potential drilling wounds. While the most effective, trunk injections that last multiple years are typically more expensive than other EAB treatments.
EAB Treatment Option: Soil Drench
  • Who applies treatment: Licensed pesticide applicators, or property owners (if ash tree is under 12” diameter at chest height)
  • Treatment process: Though soil drenches vary, they’re typically applied in the form of liquid or as granules that are then watered into the soil around the tree after the area beneath the tree has been cleared, thus allowing the soil drench to take hold in the roots of the tree
  • Frequency: The ideal frequency varies by product and the size of the ash tree being treated. But soil drench treatments should not be applied more than once a year.
  • Effectiveness: Inconsistent. In some trials, EAB control was excellent, while others yielded poor results. That said, soil drenches administered by tree professionals proved to be more effective.
  • Drawbacks: Effectiveness and environmental impact. While they proved to be better EAB control than no treatment, soil drenches are significantly more likely to fail than trunk injections. They’re also more likely to impact plants, insects or animals that may be near the tree.
EAB Treatment Option: Bark Spray
  • Who applies treatment: Licensed pesticide applicators
  • Treatment process: This formulated insecticide is sprayed on the bottom five to six feet of the ash tree using a common garden sprayer. That insecticide then penetrates the bark and is transported systemically throughout the tree.
  • Frequency: Once a year
  • Effectiveness: Inconsistent. The results of effectiveness testing on bark sprays have yielded similar results when compared to the testing on soil drenches.
  • Drawbacks: Effectiveness and environmental impact. Pesticide can blow onto adjacent plants, potentially impacting plants, insects or animals nearby.
EAB Treatment Option: Remove & Replace
  • Who applies treatment: Licensed tree care professionals
  • Treatment process: While some property owners may be savvy enough to plant a tree on their own, removing a tree is a complicated process that requires a tree professional – often times for permitting reasons
  • Frequency: Just once
  • Effectiveness: 100 percent. While getting a new tree to take hold presents its own challenges, removing and properly disposing of an ash tree is 100 percent effective at controlling the spread of EAB.
  • Drawbacks: Losing a tree that may have intrinsic value to the property owner