Box tree caterpillar in Wingham.
Box tree caterpillar (Cydalima perspectalis) is now a major threat to box hedges in Kent, alongside blight. The caterpillar was accidentally introduced from Asia via European nurseries in the mid-2000s and has spread rapidly. Greater London has been the epicentre; Kent, Surrey and Sussex are firmly inside the established zone. In a bad year a hedge can be stripped in weeks.
If you have box in Wingham, plan on the assumption it will be attacked. This is not "watch and wait" any more.
Life cycle to know
The moth has at least two generations a year in the UK, with damage running March to October. Two adult flights matter for control timing:
- From around June: first adult flight, laying eggs on box.
- Late summer: second flight. Timing varies by year, so a pheromone trap or regular checks help you catch it.
Adults are small white-and-brown moths with a dark border on the wings. Caterpillars are green with black stripes and a shiny black head, up to about 4cm at maturity. Damage shows as skeletonised leaves, webbing between shoots, dark green frass at the base, and rapid defoliation.
Inspection cadence
- Late March. First inspection. Look for overwintered caterpillars starting to feed. Any early activity is easier to control than a mid-season swarm.
- Mid-May. Second inspection. Small caterpillars easier to spot inside the hedge structure than the fresh outer growth.
- Late June. Third inspection, timed to the first adult flush. Look for eggs on the underside of outer leaves.
- Late July / early August. Fourth inspection at the second flush.
- September. Fifth check for late-generation activity before winter.
Control options
Hand-picking
Practical on a small hedge in the first few weeks of an infestation. Wear gloves: the caterpillars are not toxic but the frass is unpleasant. Drop into soapy water. Time-consuming but chemical-free.
Bacillus thuringiensis (Bt)
A bacterial spray ingested by the caterpillar, which disrupts its gut. Only effective on active caterpillars, so timing matters. It is not selective: it will also harm other butterfly and moth caterpillars on the plant, so spray only the box and check the product label and that it is approved for garden use. This is usually the workable middle ground for a garden hedge.
Pheromone traps
Attract male moths and reduce mating success. Useful as a monitoring tool to catch the flush dates in your specific garden. Limited effect as sole control: the moth population is large enough that trap-catches barely dent it. Best used to tell you when caterpillars are about, so you know when to inspect and treat.
Insecticide sprays
Broad-spectrum insecticides work but hit pollinators and wildlife. Not recommended on ornamental garden hedges unless nothing else has worked. Ineffective inside a dense hedge because they cannot penetrate the webbing where caterpillars actually live.
When to accept it and replant
If a hedge has been fully defoliated more than once in successive seasons, or if the caterpillar and blight are both present and hygiene management has not stopped decline, the honest call is to remove the box and plant a resistant alternative. Ilex crenata, dwarf yew or Euonymus japonicus 'Green Spire' all work. See the box blight guide for the replacement discussion.
What we do on box hedges
For clients with established box in Wingham gardens we can integrate an inspection routine into the annual maintenance visit: check for early caterpillar activity in March, June and August, advise on treatment timing, and follow a hygiene routine on clippings and tools. We are also happy to advise on replant timing if the hedge has passed the point where management works.
When to get a professional in
If you would rather have someone with the right kit and the local knowledge do it, send a postcode and a photo to hello@winghamhedges.co.uk or WhatsApp 07763 100 477. Fixed price, no charge if you don't accept the quote.
For other sap-sucking pests on CT3 hedges, including woolly aphid on pyracantha and cotoneaster, woolly beech aphid on chalk-side hedges, and euonymus scale on Japanese spindle, see the woolly aphid and scale insects guide.
Sources: RHS pest guidance on Cydalima perspectalis; Butterfly Conservation, advice note on box moth.