What's eating my winter gem boxwood?

Winter Gem Boxwood is a Korean boxwood (Buxus microphylla) cultivar with somewhat better disease tolerance than European boxwood but is still vulnerable to boxwood leafminer, boxwood psyllid, and box blight. Box tree caterpillar, spreading across the UK and parts of North America, is now the greatest acute threat. Voles chew roots and stems in winter.

Blister-like mines on leaves causing yellow-orange discoloration; premature leaf drop; plant vigor declines over successive seasons. Apply systemic insecticide at adult flight time in spring (monitor with yellow sticky traps). Prune affected shoots. B. microphylla cultivars have some tolerance but are not immune.

Rapid defoliation with silken webbing; green-and-black caterpillars strip foliage to bare stems in a matter of days. Inspect regularly; spray Bt (Bacillus thuringiensis var. kurstaki) or spinosad on young caterpillars. Remove webbing manually. Repeat applications every 2–3 weeks during the growing season.

Brown leaf spots, rapid defoliation, and black stem cankers — worst in warm, wet weather or overcrowded plantings. Remove all fallen leaves and debris. Apply preventive fungicide (tebuconazole, trifloxystrobin) in spring and autumn. Avoid overhead irrigation; space plants for airflow.

Gnawed roots and bark just below and at the soil surface in winter; plants wilt and collapse in early spring. Hardware cloth cylinders buried 15 cm (6 in) into the soil around the root zone. Reduce mulch depth next to stems. Rodenticide baits in enclosed bait stations where permitted.