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 York 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 is established in Southern Maine. It was first confirmed in Portland, Maine’s “Forest City,” in 2019.[3] Any ash tree in York should be considered at risk.
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.
Protecting York ash trees, step by step
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]
What the proposed quarantine repeal means
In July 2026, the Maine Department of Agriculture, Conservation and Forestry proposed ending the state’s emerald ash borer quarantine rules. The state said the beetle has spread anyway and proposed shifting its focus to education and tracking the beetle’s spread.[7] Changing the rules does not change the risk: for ash trees in York, treatment is still the only way to keep a valuable ash alive.
Want the full picture? Read our complete guide to emerald ash borer treatment in Southern Maine.
Emerald Ash Borer help near York
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 York.
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 Public: Maine wants to end emerald ash borer quarantine (July 2026)
