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]
The City of South Portland treats selected city ash trees with trunk injections to protect them from emerald ash borer.[3]
How to tell if a South Portland ash tree has emerald ash borer
First, make sure the tree is a true ash. All true ash trees are susceptible to emerald ash borer, but mountain ash is not a true ash and is not affected.[4] Early infestations are hard to spot because the damage happens under the bark. Look for these signs, especially near the top of the tree:
- Thinning leaves and dead branches, starting at the top of the crown
- Small D-shaped exit holes in the bark, about 1/8 inch across
- Patches of light-colored bark where woodpeckers have flaked away the outer bark to reach larvae
- Shoots sprouting from the trunk or base of the tree
- Vertical splits in the bark with S-shaped tunnels underneath
Protecting South Portland 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.[5]
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.[5]
- 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.
Want the full picture? Read our complete guide to emerald ash borer treatment in Southern Maine.
Ash trees and tree care in South Portland
Emerald Ash Borer help near South 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 South 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
- City of South Portland: Notification of city ash tree treatment
- Maine Forest Service: Emerald ash borer
- North Central IPM Center / Michigan State University: Insecticide options for protecting ash trees from emerald ash borer (E3075)
- City of South Portland: Emerald Ash Borer news release (2024)
- City of South Portland: Emerald Ash Borer news release (2024)
- City of South Portland: Tree Protection (2024)
- Maine Forest Service: Project Canopy – Tree City USA
