Why the codling moth is such a persistent pest

The codling moth is the reason so many homegrown apples and pears end up with a brown tunnel through the core and a little heap of gritty frass at the eye end. The adult is a small, greyish-brown moth that flies at dusk, and it is easy to miss entirely. What you notice is the damage, usually in late July and August, by which point the caterpillar is safely inside the fruit and out of reach of anything you might spray on the surface.

Understanding the lifecycle is the whole game. The moth overwinters as a fully grown caterpillar in a silken cocoon, tucked into loose bark, fence posts, log stores or the leaf litter under the tree. Adults emerge from late May into June, mate, and the females lay single eggs on leaves and young fruitlets. The tiny caterpillars hatch, wander briefly across the skin, then chew their way in. They feed for three or four weeks, mostly on the seeds, then tunnel out and drop to the trunk to pupate. In a warm southern summer, a second generation flies in August and causes a second wave of damage. Anything you do to interrupt that cycle pays off.

Use pheromone traps to know what is happening

Before doing anything else, find out whether you have a problem and when the moths are flying. A pheromone trap — a small sticky card inside a weatherproof tent with a female scent lure — will catch male moths and give you a running count. Hang one in the canopy at about head height in mid-May, before you expect the first flight, and check it weekly.

• One trap is plenty for a small garden; three or four trees can share it.
• Reckon on action if you are catching more than about five to eight moths a week in a single trap.
• Sustained catches mean the second generation is building, so tighten up on hygiene in August.
• Replace the lure every six to eight weeks and keep the sticky base free of debris and other insects.

If you grow a fair number of trees in a reasonably sheltered spot, mating disruption dispensers are worth considering. These release a cloud of synthetic pheromone that confuses males searching for females. They work well in larger gardens and small orchards, but they need to be put out early and used across the whole area to be effective.

Encourage birds, earwigs and other allies

A garden with a healthy population of insect-eaters will always have fewer codling moths than a bare one. Blue tits and great tits are the stars here: they pick caterpillars and pupae out of bark crevices through the winter and take larvae from the tree in summer. Put up a couple of nest boxes by February and keep feeders topped up in spring, when the birds are feeding young.

Earwigs are a much-misunderstood ally. They are nocturnal hunters of moth eggs and small caterpillars, and they are easy to attract. Turn a small terracotta pot upside down, stuff it loosely with straw or shredded paper, and hang it in the branches from July onwards. Check and top it up each year.

• Avoid broad-spectrum insecticides entirely — they kill the predators as readily as the pest.
• Leave a wild patch or a hedgerow nearby for shelter and overwintering habitat.
• Wasps, despite their reputation, take caterpillars from fruit in late summer.

Collect fallen fruit — and check what you are collecting

This is the single most useful job in a British fruit garden, and the cheapest. A caterpillar that has finished feeding leaves the fruit and drops to the trunk, often on the same day the fruit falls. Leave windfalls lying about and you are simply rearing next year's moths.

Walk the tree every day or two from early July through to October, and pick up everything on the ground. Do not assume every fallen apple is infested: June drop in early summer is a natural thinning of unpollinated fruit and usually carries no larvae. Cut a few open and look for the tunnel before you decide.

Dispose of infested fruit properly. Burying it deep, drowning it in a bucket of water for a few days, or bagging it for the council green waste is fine. Adding it to a cool compost heap is not — the caterpillars will simply crawl out and pupate in the heap.

Trunk bands, bark cleaning and winter housekeeping

Corrugated cardboard bands tied around the trunk in July give caterpillars a tempting place to spin up. They will use it in preference to rough bark. Take the bands off in late autumn and burn or bin them — that single action can remove a large proportion of the overwintering population.

In winter, when the tree is dormant, go over the trunk and main branches with a stiff hand brush to remove loose, flaking bark where cocoons hide. Clear leaf litter from the base of the tree, remove any shrivelled, mummified fruit still hanging, and scrub out the corners of your fruit store, shed and boxes. If you have chickens, let them scratch under the trees through the winter; they will find pupae you cannot see.

There are also gentle biological controls worth using. Nematodes watered onto the trunk and around the base in autumn will seek out and kill overwintering larvae, and a codling-moth-specific virus product is available for garden use — check what is currently approved and follow the label carefully. Kaolin clay sprays, applied from June, put a chalky barrier between the caterpillar and the skin, though they need re-applying after rain and leave fruit looking dusty.

Pulling it all together through the season

No single measure will give you a completely clean crop, and you should not expect one to. The aim is to stack several small, sensible actions on top of each other until the moth population collapses to a level you can live with.

• May: hang pheromone traps, put up nest boxes and start weekly counts.
• June: begin kaolin sprays if you use them, and start daily windfall collection.
• July: fit cardboard trunk bands and hang earwig shelters.
• August: keep collecting fallen fruit relentlessly through the second flight.
• October: remove and destroy bands, apply nematodes, brush bark.
• Winter: clear litter, clean the fruit store, tidy boxes and crates.

Do this for two or three seasons and you will notice the difference. You will still lose the odd apple, and honestly, the odd one is a fair price for fruit you can eat straight from the tree without worrying.