Codling moth

What you are looking at

An apple picked in September has a small round hole in the side or at the eye end, sealed with a plug of wet brown crumbs. Cut it open and a tunnel runs to the core, the pips have been eaten, and the cavity is packed with dry frass. A pinkish-white caterpillar with a brown head may still be in there, up to about 2 cm long.

Some affected fruit colours and ripens ahead of the rest of the tree and falls early, which is worth knowing at the end of August when a few apples come down looking finished.

Pears get it less often and walnuts get it too, with the larva going into the developing kernel.

Codling moth or apple sawfly

Both put a maggot in an apple and the treatments differ, so the distinction is worth five seconds.

Apple sawfly attacks in May and June, when the fruitlets are small. Its larva often tunnels just under the skin first, leaving a winding ribbon-like scar that corks over and stays on the apple all season as a brown band. When it goes into the core the frass is wet, dark and smells strongly. Most sawfly-damaged fruitlets drop in the June drop.

Codling moth comes later. Eggs are laid from June onwards on fruit and leaves, and the caterpillar bores in and heads straight for the core. The entry hole is neat and round, the frass is dry and crumbly, and the fruit stays on the tree to be picked with the damage inside it.

A ribbon scar on the skin of a picked apple is sawfly. A frass-plugged hole is codling.

One generation, and where it spends the winter

Adults fly at dusk from late May or June through July, a grey-brown moth about 10 mm long with a bronze-coppery patch at the tip of each forewing. Britain gets one generation in most years and a partial second after a hot summer.

Eggs hatch within a fortnight and the caterpillar enters the fruit. It feeds for three to five weeks, leaves through a tunnel of its own making, and crawls down the branches to find a crevice. There it spins a tough silk cocoon, under a flap of loose bark, in a crack, behind a tree tie, or in a fruit crate stored in the shed. It sits there through the winter as a full-grown larva and pupates in spring.

Every control worth doing follows from that itinerary. Windfalls collected before the larva leaves, a cardboard band offered as the crevice it is looking for, nematodes sprayed into the real crevices in autumn, and tits working the bark all winter.

What to do about it

Tie a corrugated cardboard band around the trunk in July and burn it in late autumn.

Collect windfalls twice a week from August and bin the damaged ones.

Hang a pheromone trap from late May, and read it as a calendar unless your tree stands well away from other apples.

Spray nematodes over the trunk and main branches on a mild damp evening in early autumn.

Scrape loose bark and wash out the fruit crates in winter.

Put up a nest box.

Then accept that some fruit will be lost, because a garden apple tree in Britain has never produced a clean crop without a spray programme, and a clean crop is not what most people are growing one for.

What it gets mistaken for

Apple sawfly leaves a ribbon scar and wet smelly frass, and drops most of its fruitlets in June.

Brown rot turns the flesh brown and firm and grows rings of buff-coloured pustules on the skin. It commonly starts at a codling moth hole, so the two are found together.

Bitter pit shows as small sunken brown spots scattered under the skin with no tunnel and no insect, and it is a calcium transport problem rather than a pest.

Wasps enlarge existing wounds into open ragged craters and eat the flesh from outside. They rarely break intact skin.

Apple scab leaves black scabby blotches on the surface that crack the skin, with sound flesh beneath.