Emerald ash borer is a small, metallic-green beetle whose larvae tunnel under the bark of ash trees and cut off the flow of water and nutrients. Untreated ash trees usually die within a few years of becoming infested. All of Cumberland County is inside Maine’s emerald ash borer quarantine,[1] and in 2026 the Maine Forest Service reported ash dieback and mortality throughout the southern part of the state.[2]
Emerald ash borer was first confirmed in Portland, Maine’s “Forest City,” in 2019.[3]
Treat or remove? The 50% rule
Maine’s ash treatment guide does not recommend treating ash trees with more than half of their fine branches dead, and recommends removing ash that is dead or has more than 50% crown dieback.[4] Ash trees injured by emerald ash borer become brittle,[5] so waiting too long can turn a treatable tree into a hazard.
Our ash tree treatment in Portland
Injected treatments travel up through the tree’s vascular system, so they work best on ash trees with a mostly full canopy. Trees that are already declining may keep declining through the first year after treatment, then usually improve in the second.[6]
Is your ash worth saving?
A healthy, well-placed ash tree that shades a home or street is often worth protecting. Removing a large tree, replacing it, and losing its shade all have costs, and Maine’s treatment guide suggests weighing them.[4] A tree health assessment helps you decide which trees on your Portland property are worth treating.
Want the full picture? Read our complete guide to emerald ash borer treatment in Southern Maine.
Ash trees and tree care in Portland
Emerald Ash Borer help near Portland
Tree Medics is based in Biddeford and works throughout Southern Maine. We also offer emerald ash borer services in nearby towns:
See all tree care in Portland.
Sources
- Maine Forest Service: EAB found in seven more Maine towns, with York and Cumberland counties under quarantine (2020)
- Maine Forest Service: Forest & shade tree conditions, August 2026
- Maine DACF: Emerald ash borer discovered in Portland, Maine’s “Forest City”
- Maine Forest Service: Ash treatment guide
- Maine Forest Service: Emerald ash borer
- North Central IPM Center / Michigan State University: Insecticide options for protecting ash trees from emerald ash borer (E3075)
- Maine DACF: Emerald Ash Borer Discovered in Portland, Maine’s “Forest City” (2019)
- Maine Public: Beetle Connected To Ash Tree Deaths Found In Portland (2019)
- Maine Forest Service: Project Canopy – Tree City USA
- Maine DACF: 2023 Project Canopy Grants Announced (2023)
