What's eating my korean arborvitae?

Korean Arborvitae is a less commonly cultivated species and relatively pest-resistant, but shares the Thuja vulnerability to spider mites and scale. Bagworms are a threat where this species is grown ornamentally. Its naturally compact, slow-growing habit means pest damage is slow to recover. Deer will browse if no preferred food is available.

Fine webbing and dusty bronze discolouration on foliage; older interior growth drops first; compact growth habit means infestations can rapidly discolour the whole plant Apply horticultural oil before bud break; insecticidal soap or bifenazate miticide during active infestations in spring or autumn; ensure adequate soil moisture throughout summer

Foliage-and-silk bags attached to branch tips; larvae feed on foliage within bags; small or slow-growing specimens can be significantly set back by even moderate infestations Hand-remove bags in winter before eggs hatch; spray Btk at larval hatch in late spring; spinosad or bifenthrin for heavier pressure

White-grey armoured scales on foliage and stems weaken the plant; yellow discolouration and sparse foliage result from sustained sap loss; sooty mold may follow Horticultural oil at crawler stage in late spring; systemic imidacloprid soil drench; prune out heavily infested areas and monitor annually