ORGANIC CODLING MOTH CONTROL

© Frances Michaels

Everyone knows the old joke 'What is worse than finding a worm in your apple?' Answer 'Half a worm' which refers to the larva of the Codling moth (Cydia pomonella), which originated in Europe but is now found in most countries that grow apples. It also attacks pears, quinces, and occasionally walnuts and stone fruits.

LIFECYCLE:
In early spring the moths emerge about the time the fruit trees are in full bloom. The adult moths are about 10 mm long with a 20 mm wingspan, the wings are grey with fine brown bands. There is a metallic copper-coloured patch near each wingtip and the hind wings are fringed. Tiny, pinhead-sized eggs are laid by each female moth after dusk, usually on leaves, once the temperature is 15°C or higher. The eggs hatch in about 10 days. The tiny caterpillars may feed for a while on leaves before moving into the fruit. The caterpillar chews its way into the fruit core, where it feeds for 3-5 weeks. When it leaves the fruit and moves down the trunk and branches it searches for a suitable place to spin a cocoon. This might be under loose bark, in a crevice or in the ground. As the weather begins to cool down the last larvae do not pupate immediately but remain in their cocoons for some months. There are usually 2-3 generations a year in Australia.

Codling moth photos courtesy of Denis Crawford of Graphic Science

BIOLOGICAL CONTROLS

• The most important natural enemy of the codling moth is the Trichogramma micro wasp, which parasitises the moth eggs, by laying its egg inside the moth egg. The wasp larva then feeds on the contents of the moth egg. One female wasp is able to parasitise over 50 moth eggs. Trichogramma wasps are commercially produced in Australia. The adult micro-wasp feeds on insect eggs, nectar, and pollen, a good food supply means it lives longer. Growing suitable plants under the fruit trees as a pollen and nectar source helps to maintain a population of these beneficial insects. Suitable plants include clover, buckwheat, mustard, Queen Anne’s lace, parsnip, daikon, alyssum, dill, coriander and cosmos.

• Other natural enemies of codling moth include tachinid flies, ichneumon wasps, braconid wasps, chalcid wasps, carabid beetles, earwigs and ants. Spiders eat codling moth eggs, moths and larvae.
• Night flying birds, tree frogs and small insectivorous bats will also reduce moth numbers.
• Design your orchard area to be a poultry forage system, the chooks will turn damaged fruit into eggs and help to control a wide range of pests including codling moth. Do not introduce poultry into a young orchard, as the poultry will scratch at the mulch, exposing the roots. Where it is undesirable to allow chooks free range, small demountable fences can be used under specific trees.

PHYSICAL AND CULTURAL CONTROLS

• The apple season is a peak time to work on your organic strategies for codling moth. Inspect the trees every 10 days, collect any fruit you find with small holes and destroy it by immersing it in water for several days. Alternatively place it in a sealed, black plastic bag in the sun, and then try feeding it to poultry.
• Remove loose bark and leaf debris from the crotch of the tree, to reduce hiding places for cocoons. Corrugated cardboard bands can be placed around trunks and limbs to trap caterpillars looking for a place to pupate. Inspect every 3 weeks and destroy any cocooned caterpillars. The most important trapping time is winter and spring but for effective control inspect the bands all year round.
• Open-mouthed jars can be filled with a variety of baits to attract codling moth. Try port diluted with water (1 part port to 9 parts water), fermenting apple juice, molasses or oil of cloves. Add a film of vegetable oil to the top to stop moths from escaping and prevent mosquitoes breeding. Hang them in trees in the warmest part of the orchard. Studies have shown codling moth prefer a bait 4-5 days old. Replace the baits every 2 weeks.
• Light traps, to attract the moths, can be made by suspending a light globe above a pan of water topped with a thin film of kerosene.
  Research has shown that using overhead irrigation from 7 to 11pm every night for 2 months during the period of intense moth activity reduced fruit injury by 90%. This was related to a climatic study that found rainfall increased larval mortality and decreased egg laying
• A good choice for the home gardener with only a few apple trees is to bag the fruit. Commercial exclusion bags are available in either waxed paper with a built-in twist tie or cloth with a drawstring. Bags should be placed over the fruit while it is very small, first thin the fruit to one piece. It is a good idea to spray before bagging to kill any small caterpillars already present. Bags should be removed 4 days before harvesting to allow the fruit to develop a stronger red colour. A big advantage to exclusion is it usually helps deal with bird and possum problems as well.
• A horticultural glue such as Trappit Barrier Glue or Tanglefoot Glue around the trunk of the tree will prevent the movement of some of the female moths from the ground into the tree, as they tend to crawl and flutter up the branches. It should be in place from the first moth sighting until mid-winter. Using the glue below the corrugated cardboard bands will also help to force the larvae looking for a pupation site into the cardboard bands, as it will make it more difficult for them to reach the ground.
   

LEAST TOXIC CHEMICAL CONTROLS

• Least-toxic sprays such as garlic or pyrethrum can be used to control the adult moths, once traps have shown that they are active and to kill tiny caterpillars before they enter the fruit. Spray in bark crevices and under the leaves where the moths will be hiding. There may be some damage to populations of beneficial insects with the use of pyrethrum sprays. A Pest Oil spray can be used to smother the moth eggs, it should be applied 4 to 5 times beginning at petal fall and then at 10 day intervals. Dipel contains Bacillus thuringiensis, or Bt for short; it is an organic bacterial control for caterpillars. To have any effect on codling moth caterpillars it must be timed carefully; once the caterpillars are safe inside the fruit, it will have no impact. Combining 1% Pest Oil with Bt may improve the effectiveness.

•  A pheromone is a non-toxic species-specific scent produced by the female insect to attract the male. Pheromones are a particularly useful control for codling moth as they do not travel very far, usually under 60 metres, and find each other entirely by scent. Synthetic pheromones are used in two different ways:

  1. Desire Codling Moth Traps are a new generation codling moth trap that attracts both MALE and FEMALE moths for the whole season. They are used to monitor the mating activity of codling moth and also will significantly help in control. They allow you to be aware of when codling moths become active and correctly time your control program.

  2. Pheromones are also used for mating disruption. By using Isomate twist ties the orchard area is saturated with pheromones making it extremely difficult for codling moths to find each other in order to mate. This technique is only suitable for larger blocks of at least 1 hectare; it is unlikely to work well in a small area.

   

  Suggested Products:

  Apple Pouch

  Codling Moth Trap

  Dipel®

  Horticultural glue

  Pest Oil

  Exclusion Bags