Box tree moth
Green-and-black caterpillars that strip boxwood hedges and topiary, leaving webbing and bare, brown patches. A major pest in the UK and Europe, now spreading in North America.
Also known as: Box tree caterpillar, Cydalima perspectalis
Symptoms and identification
Leaves are eaten, leaving only the midribs, with fine webbing and green droppings inside the plant. Patches of the hedge turn brown and bare, often from the inside out.
Causes
An invasive moth from East Asia that lays eggs on box leaves; several generations of caterpillars can feed from spring to fall.
Organic treatment
Pick off caterpillars and webbing by hand. Spray Bacillus thuringiensis (Bt) when young caterpillars are active, reaching inside the plant. Nematode sprays also work.
Prevention
Check inside box plants regularly from early spring. Use pheromone traps to monitor moths.
Chemical treatment (use with care)
Use an insecticide labelled for box tree caterpillar, following the label.