Tree and shrub services in Portland, Maine.

All of Cumberland County is inside Maine's emerald ash borer quarantine. The Maine Forest Service notes that every native ash species is susceptible, that infested trees become brittle, and that property owners should find out whether EAB is a concern for their trees. On an ash, pruning decisions now start with its health and whether keeping it makes sense. The agency also points out that mountain ash is a different genus and is not attacked, which is worth knowing before a healthy tree is written off by name alone.

Winter moth is established along the coast from Kittery to Bar Harbor and feeds on oak, maple, apple, elm, ash and cherry. Three or more years of heavy defoliation can cause branch dieback. Browntail moth webs can be clipped from low branches between October and March, and the Forest Service says anything off the ground or near hazards is work for a licensed arborist.

Portland's pesticide ordinance, which otherwise bans synthetic products on private property, carves out exceptions for treatments for heritage elms and for controlling emerald ash borer, hemlock woolly adelgid, browntail moth and other insects the Maine Forest Service identifies as invasive.