What's eating my chinese arborvitae?

Chinese Arborvitae (Platycladus orientalis, formerly Thuja orientalis) is heavily targeted by bagworms and spider mites in cultivation. Scale insects and leafminers also occur. In warm climates, bagworms are the most destructive pest, capable of killing plants outright. Deer show moderate interest; rabbits may bark-strip young stems.

Larvae encase themselves in silk-and-foliage bags attached to branch tips; feeding strips foliage; heavy infestations rapidly defoliate and can kill Chinese Arborvitae, which tolerates defoliation poorly Hand-remove bags in winter before eggs hatch; spray Btk or spinosad at larval hatch (late May–June) for best efficacy; bifenthrin or permethrin for large infestations on mature trees

Scale-like foliage turns dusty bronze or grey-yellow; fine webbing on branch interiors; needles drop prematurely from the centre outward; worst in hot, dry conditions Horticultural oil dormant spray; insecticidal soap or miticide (bifenazate) during cool growing-season windows; regular irrigation reduces stress susceptibility; avoid overhead stress in summer

Larvae mine inside foliage sprays, causing tan-to-brown tip dieback that can be mistaken for drought; interior dieback progresses outward if multiple seasons of mining occur Spray spinosad or insecticidal soap in late May–June targeting newly hatched larvae; prune and destroy mined sprays; imidacloprid systemic treatment for recurrent infestations

Tiny white-grey armoured scales coat foliage and stems; sucking reduces plant vigour; foliage turns yellow then brown; sooty mold may develop on honeydew from adjacent soft scales Apply horticultural oil at crawler emergence in late spring; systemic imidacloprid soil drench; prune out and destroy heavily scaled stems; introduce natural predators where feasible