What's eating my hiba arborvitae?

Hiba Arborvitae (Thujopsis dolabrata) is susceptible to spider mites in hot, dry conditions, which cause browning and needle drop. Bagworms and scale insects are occasional threats, particularly in North American gardens. Deer and rabbits will browse foliage during winter. The tree is generally robust and pest-resistant in cool, humid climates.

Greyish-bronze stippling and fine webbing on foliage, especially interior; needles drop prematurely in dry summer heat. Water trees adequately to reduce heat stress. Spray foliage with water forcefully every few days. Apply miticide (bifenazate or neem oil) if infestation persists.

Conical bags constructed from foliage fragments hanging on branches; defoliation of enclosed shoots; branch dieback. Hand-remove bags before eggs hatch in late spring. Spray Bacillus thuringiensis (Bt) or spinosad targeting young larvae in early summer.

White encrusted scales on foliage and stems; yellowing and thinning of needle cover over several seasons. Apply dormant horticultural oil spray in late winter. Repeated applications of insecticidal soap during the growing season for crawlers.