Plants affected
Apples, pears, and less frequently, quinces, walnuts.
Symptoms
The maggot's exit hole is often visible in the side of the
ripe fruit or at the 'eye' end, (opposite to the stalk). When
the fruit is cut open you can see the frass-filled core and
tunnel where the maggot had been feeding.
Cause
Adult codling moths emerge in late May and lay eggs on or near developing fruits from June to mid-July. After hatching, the small white, brown-headed caterpillar bores into the fruit and feeds in the core region. This pest overwinters as non-feeding caterpillars under loose flakes of bark and they pupate in the following spring.
Control
Codling moth caterpillars can only be controlled on apple and pear before they enter the fruit. On trees small enough to be sprayed, the newly hatched caterpillars can be killed by using bifenthrin (Scotts Bug Clear Gun, Doff All-In-One Garden Pest Killer or Bayer Sprayday Greenfly Killer Plus). Use one of these in about the third week of June with a second application about three weeks later. In some years egg hatching may be earlier or later due to the weather conditions. It is not worthwhile spraying quince or walnut as the level of infestation in these fruits is rarely significant, and bifenthrin is not approved for use on these plants.
A pathogenic nematode (Steinernema carpocapsae) is available by mail order from some suppliers of biological controls. This is a microscopic worm-like creature that enters the bodies of caterpillars and infects them with a fatal bacterial disease. The nematode should be sprayed on the trunk and branches, and also the soil under the branches, in September-October, after the caterpillars have left the fruit. This treatment gives no protection next year against female codling moths flying in from nearby gardens and so may not be worthwhile in areas where apples and/or pears are widely grown.
Pheromone traps
More accurate timing of spray applications can be achieved using a codling moth pheromone trap, which is available from most garden shops. This consists of an open-sided box that is hung in the tree in early May. The bottom of the box has a sticky sheet on which the pheromone pellet is placed; this exudes a scent similar to that produced by virgin female codling moths to attract mates. Male moths are lured into the trap and get stuck. By counting the trapped males every week and following the instructions that come with the trap, the best time to spray can be calculated. A pheromone trap on its own cannot control codling moths, but on isolated trees it may catch enough males to reduce the females' mating success, resulting in fewer fertile eggs being laid. Pheromone traps sold by Agralan are designed to prevent birds entering the trap and getting caught by the sticky sheet.