Why do my apples have a hole and a maggot inside?

Telling codling moth from apple sawfly by the damage they leave, and the traps, hygiene and timing that reduce the population without spraying a tree in flower.

Difficulty: beginner
Time: 45 min
Read: 5 min

Short answer

A single tunnel to the core, brown crumbly frass at the eye or the side, and a pinkish-white caterpillar means codling moth. Hang a pheromone trap per tree from mid-May, pick up and destroy every fallen and grubby apple, scrape loose bark in winter and put up grease bands or corrugated cardboard traps. There is no cure for an infested apple.

Codling moth lays its eggs on developing fruit and leaves from late May to July. The caterpillar bores into the apple, feeds around the core, and leaves through a hole plugged with frass before pupating under loose bark or in leaf litter to overwinter. Because the damage happens inside the fruit, everything you do is about reducing next year's population and knowing when the moths are flying, not about rescuing this year's crop.

What you'll need

Codling moth pheromone traps
Bags for infested fruit
Corrugated cardboard for winter trapping (optional)
Wire brush for loose bark (optional)

Step by step

Confirm it is codling moth and not sawfly.Codling moth: a single tunnel to the core, entry hole plugged with brown crumbly frass, damage found at picking time, caterpillar pinkish-white with a brown head. Apple sawfly: a ribbon-like scar winding over the skin, a wetter darker frass, damage in June, and the caterpillar smells unpleasant when the fruit is opened.
Hang pheromone traps from mid-May.One trap per tree, or one per five metres in a small orchard, hung at about head height on the sunny side. They catch male moths and, more usefully, tell you when the flight is happening — a run of catches means eggs are being laid.
Pick up and destroy fallen fruit weekly through summer.Each infested windfall contains a caterpillar that will leave and overwinter successfully if you leave it there. Bag it or bury it deeply; do not compost it in a cool heap.
Take grubby fruit off the tree when you spot it.A fruit with a frassy hole is already lost. Removing it before the caterpillar leaves takes that individual out of next year's population.
Trap overwintering caterpillars in autumn.Tie bands of corrugated cardboard, ridged side inwards, around the trunk and main limbs in late summer. Caterpillars pupate in the corrugations. Remove and destroy the bands in winter.
Scrape loose bark in winter.Flaking bark and old wounds are where they overwinter. A wire brush over the trunk and main limbs on a dry winter day, with a sheet underneath to catch what falls, removes a lot of them.
Encourage the things that eat them.Blue tits eat overwintering caterpillars, so a nest box near the tree genuinely helps. Bats take the adult moths.
Treat chemical control as a last resort and check the current label.Any product must be approved for edible fruit and used exactly as directed, and timing has to match the egg hatch, which is why the pheromone trap matters more than the spray. Never spray a tree in flower — it kills pollinators, and there is no fruit to protect yet anyway.

Tips

Pheromone traps are a monitoring tool first. On a single garden tree they also reduce mating enough to make a real difference; in a neighbourhood full of apples they will not eliminate the problem.
Damage is usually worse in a warm dry summer, which allows a partial second generation in the south.
Early varieties are often picked before the worst of the damage. Late keepers take the brunt.
A grubby apple is perfectly edible once the tunnel is cut out — it simply will not store, so use those first.
Codling moth also attacks pears and, occasionally, quince and walnut.

Common mistakes

Leaving windfalls under the tree — Every infested one releases a caterpillar to overwinter and come back. Picking up fallen fruit weekly is the single most effective control there is.
Spraying at blossom time — There is no fruit for the moth to lay on yet, the eggs have not been laid, and you kill the pollinators the crop depends on.
Composting infested apples in a cool heap — The caterpillar simply completes its life cycle in the heap. Bag them, bury them deep, or use a hot heap.
Confusing codling with sawfly and timing control for the wrong pest — Sawfly damage happens in June and is controlled by removing damaged fruitlets early. Codling damage shows at picking. The two need action in different months.

If it doesn't work

Hole plugged with dry brown frass, tunnel to the core, at picking time

Cause: Codling moth — Fix: Traps from mid-May, destroy fallen and grubby fruit, cardboard bands in late summer, scrape loose bark in winter.

Ribbon-shaped scar across the skin, or a wet frassy hole in June

Cause: Apple sawfly — Fix: Pick off and destroy affected fruitlets in June before the larva moves on to a second fruit. Damaged fruit that survives is scarred but edible.

Small maggots and rotting flesh around a wound

Cause: Secondary invaders after wasp or bird damage — Fix: Deal with the original wound source; the maggots are following, not causing, the damage.

Every apple affected, year after year

Cause: High local population and untidy overwintering sites — Fix: Combine all the cultural measures at once for two seasons, and get neighbours with apple trees to pick up their windfalls too.

Questions people ask

Are apples with codling moth safe to eat?

Yes. Cut out the tunnel and the frass and the rest of the fruit is fine. It will not store, so use damaged fruit first.

When do codling moths fly?

From about mid-May to July in the UK, with a partial second generation in warm southern summers. A pheromone trap tells you what is happening in your own garden, which varies year to year.

Do pheromone traps actually work?

As monitoring, reliably. As control on an isolated garden tree, they help noticeably. In an area full of apple trees they will not solve it alone, and the hygiene measures do most of the work.

What is the difference between codling moth and apple sawfly?

Sawfly damage appears in June as a winding ribbon scar on the skin, often with wet frass, and the caterpillar smells strongly. Codling damage is found at picking, with a single clean tunnel to the core and dry crumbly frass.