What's eating my japanese arborvitae?

Japanese Arborvitae faces the same core pest threats as other Thuja species: bagworms, spider mites, and scale insects. In its native Japan and in UK cultivation, the green spruce aphid and leafminers may also occur. Deer readily browse this species. It is considered moderately pest-resistant compared to Thuja occidentalis.

Spindle-shaped bags attached to branch tips; larvae strip foliage from within bags; repeated defoliation weakens and can kill branches or smaller specimens Hand-pick bags in winter; apply Btk or spinosad at larval hatch; bifenthrin spray for heavy infestations; destroy removed bags off-site to prevent re-infestation

Foliage bronzes and takes on a dull, dusty appearance with fine webbing on branch undersides; needle drop progresses inward; worst in cool, dry spring and autumn weather Dormant horticultural oil spray; insecticidal soap or miticide at early infestation; overhead watering helps suppress mite populations in dry conditions

Soft brown scales on stem bases and foliage produce honeydew leading to sooty mold; heavy infestations cause yellowing, flagging, and eventual dieback of affected branches Dormant oil spray in late winter; insecticidal soap at crawler emergence in June; dinotefuran systemic treatment for persistent scale; prune heavily infested shoots