Tree of heaven (Ailanthus altissima) is a Class C noxious weed in King County. Property owners are encouraged to control it; nurseries are barred from selling it. The species hosts spotted lanternfly, a feared invasive pest.
The King County Noxious Weed Control Board, operating under Washington RCW 17.10, classifies tree of heaven (Ailanthus altissima) as a Class C noxious weed. Class C means landowner control is encouraged but not mandated; nurseries cannot sell it under WSDA quarantine. The tree colonizes disturbed soil along I-5, alleyways, and abandoned lots. It is the preferred host of spotted lanternfly, an Asian planthopper not yet established in Washington but quarantined nationally; early ailanthus removal is a key prevention strategy. Removal requires repeated cut-stump or basal bark herbicide because the tree resprouts vigorously from roots. King County offers free identification visits. Seattle Tree Protection Code (SMC 25.11) does not protect noxious-weed species.
Class C: no automatic county fine, but selling or distributing is prohibited (WSDA penalty up to $1,000). Spotted lanternfly host material movement: state quarantine violations.
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