What's eating my common box?

Common box faces three serious threats: box tree moth caterpillars can completely defoliate plants in weeks, boxwood leafminer causes blistered leaves year-round, and box blight fungal disease causes rapid dieback. Boxwood psyllid and spider mites add pressure. Regular monitoring, pheromone traps for the moth, and prompt treatment are essential.

Lime-green caterpillars with black stripes window the leaves and skeletonize foliage, progressing to complete defoliation. Webbing inside the plant is a diagnostic sign. Can kill plants if left unchecked. Check plants regularly from spring onwards; remove caterpillars by hand or use an approved insecticide (spinosad, lambda-cyhalothrin, or pyrethrin). Use pheromone traps to monitor adult moth flight. Multiple treatments per season are needed.

Larvae mine between leaf surfaces, producing blistered, discoloured, pale-green or orange patches on leaves. Heavily infested foliage drops prematurely. Apply a systemic insecticide (imidacloprid, thiamethoxam) in spring at egg-hatch, or spray foliage with bifenthrin timed to adult fly emergence in May–June. Prune out and destroy badly affected growth.

Immature psyllids cause cupped, stunted shoot tips in spring. Affected leaves are slightly sticky with honeydew and visible waxy white secretions. Damage is mainly cosmetic. Clip off cupped shoot tips in late spring after adults have dispersed. Spray with insecticidal soap or pyrethroid in early spring when nymphs first appear. Not usually worth treating unless aesthetic impact is high.

Feeding causes fine pale stippling and bronzing of the upper leaf surface. Damage accumulates over the season; not always noticed until plants look dull and off-colour. Apply horticultural oil or a miticide in spring. Encourage natural predators (phytoseiid mites). Avoid dusty conditions and water stress, which favour mite population build-up.