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Box tree caterpillar tops the list of garden pests

Posted on Saturday 26th March 2016
close up of the Box tree caterpillar on box leaves

The RHS has revealed the top ten pests for 2015 based on reported enquiries to the RHS Gardening Advice Team during that year.  Box tree caterpillars have emerged as the number one pest, followed closely by slugs and snails.  Box tree caterpillars, which cause severe defoliation of box plants, are prevalent in the South east of England but it’s predicted that the problem will gradually spread to other parts of the UK.

About the Box Tree Caterpillar:

  • Box tree caterpillars are the larvae of a moth (Cydalima perspectalis) that is native to East Asia. The moth typically has white wings edged brown and a 4cm wing span.
  • The female moth lays sheets of yellow eggs on the underside of the box leaves.
  • Newly hatched caterpillars are greenish-yellow with black heads reaching up to 4cm in length as they mature and developing black and white stripes along the length of the body.
  • The pupae are surrounded by a cocoon of white webbing.
  • Several generations of caterpillars may be produced between April and October.
  • Young caterpillars will overwinter in the box plant, well concealed by webbing.

    The moth of the Box tree caterpillar moth

    The moth of the Box tree caterpillar

Symptoms:

  • The affected box plant becomes defoliated as the caterpillars feast on the leaves
  • The plant becomes partly or wholly covered in webbing.
  • Some dieback of the plant may also occur.

Non-chemical control

  • Box plants should be regularly monitored for symptoms.
  • Caterpillars and webbing should be removed and disposed of.

Chemical control

  • Serious infestations may require careful chemical control.
  • Spray in calm dull weather conditions to avoid spray drifting on to nearby flowering plants and their insect pollinators.
  • Spray very early in the morning or late in the evening when beneficial insects are least active.
  • A total chemical coverage of is essential and repeated applications throughout the season will be necessary.

Recommended chemicals:

The RHS Top Ten Pests 2015

  1. Box tree caterpillar
  2. Slugs and snails
  3. Aphid
  4. Large Cabbage White butterfly
  5. Vine weevil
  6. Cushion scale
  7. Lily beetle
  8. Rosemary beetle
  9. Fuchsia gall mite
  10. Woolly aphid
Barbara Cartwright