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 is established in Southern Maine. It was first confirmed in Portland, Maine’s “Forest City,” in 2019.[3] Any ash tree in Cumberland should be considered at risk.
Protecting Cumberland 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.[4]
When to treat
- Mid-May to early JuneThe recommended window for emamectin benzoate trunk injection. In research, one injection controlled emerald ash borer for at least two years.[4]
- SummerA good time to look closely at ash canopies. Thinning at the top of the crown is often the first visible sign.
- Fall and winterPlan ahead: we can identify and measure the ash trees on your property before the next treatment season.
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.[5] A tree health assessment helps you decide which trees on your Cumberland 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 Cumberland
Emerald Ash Borer help near Cumberland
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 Cumberland.
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”
- North Central IPM Center / Michigan State University: Insecticide options for protecting ash trees from emerald ash borer (E3075)
- Maine Forest Service: Ash treatment guide
- Town of Cumberland: Subcommittee – Forestry (2024)
