Diamondback moth

Scientific name: Plutella xylostella
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Pest of all brassica crops
  • Found throughout New Zealand
  • Moths are small – around 10 mm long
  • Moths have diamond shaped patterns on their wings while at rest
  • Caterpillars feed on underside of leaves
  • Colour varies from yellowish green to grey green.

  • Diamondback moth is common throughout the country and is a common pest of brassicas
  • The adult moths are small slender insects with a wingspan of about 10 mm. At rest the wings are held above the body and a line of yellowish diamond shaped markings become apparent hence the name
  • The moths are primarily nocturnal
  • Diamondback moth development is driven largely by temperature and one life cycle may be as quick as 12 days or as long as 126
  • Females lay their 0.5 mm eggs on the underside of brassica leaves singularly or in groups of up to 20. The moths live for about 14 days and each female is capable of producing up to 450 eggs
  • In summer these eggs usually hatch in 12 days but it can be as short as three days or in winter as long as 40
  • In warm weather the caterpillars take about 14-17 days to pass through five larval stages and grow to their final size of 10 mm long
  • They pupate on the underside of leaves in characteristic loosely woven cocoons remaining as pupae for 2-3 weeks
  • In warmer areas of the country there may be 6-7 generations per year.

  • Diamondback moth caterpillars feed on all brassica crops
  • When the larvae hatch from the egg they burrow into the leaf and feed on tissue within
  • As they grow they emerge to feed on the lower leaf surface leaving the upper surface intact. This distinguishes their feeding from that of cabbage white butterfly caterpillars
  • They often cause damage to crops and scouting the crop will allow detection of caterpillars while they are small and allow treatment before damage reaches a high level.

  • Two insect biological control agents, the wasps Diadegma semiclausum and Diadromus collaris, and a fungus, Entomophthora spaerosperma, usually exert a high level of control of caterpillars in the North Island but are considered less effective in the South Island
  • Damage by diamondback moth caterpillars often appears in combination with that of cabbage white butterfly caterpillars. Either on its own or in combination with the latter application of an insecticide can be worthwhile. Several insecticides are registered for use against diamondback moth caterpillars in forage brassica crops. These should be applied as early as possible to prevent damage becoming extensive.

Insecticide

Application

Time of application

Chlorantraniliprole Spray No more than 3 applications/season
Diazinon Spray As required
Dichlorvos Spray Restricted use
Lambda-cyhalothrin Spray No more than 3 applications/season
Maldison Spray As required

Contact:
Graham Walker
Plant & Food Research
Mount Albert Research Centre
Private Bag 92169, Auckland 1142, New Zealand
Graam.Walker@plantandfood.co.nz