Apple maggot
Rhagoletis pomonella
also called Railroad worm
A native fruit fly whose maggots tunnel brown threads through an apple, leaving the skin dimpled and the flesh unusable. Red sticky spheres, hung early, do real work.
A fly 5 mm long, smaller than a housefly, black with a white spot on the thorax and four dark bands across each wing arranged like a letter F. The maggot is a legless white grub inside the fruit; the tunnels it leaves are the narrow brown threads that give it the name railroad worm.
- Small dimples and pinprick punctures on the skin of a ripening apple.
- Winding brown tunnels through the flesh when the apple is cut, with no clean core hole.
- Apples dropping early and rotting quickly on the ground.
- Flies resting on the fruit and walking in slow circles on warm afternoons in midsummer.
- Hawthorn and crab apple nearby carrying the same damage.
It winters as a pupa in the soil under the tree and emerges from late June through August. Females lay single eggs under the skin of the fruit; the maggot feeds inside for several weeks, drops with the apple, and burrows into the ground to pupate. One generation a year, with some pupae lying over for two winters.
A native of hawthorn that moved onto apples, so gardens with wild hawthorn, crab apple or an abandoned apple nearby have the highest pressure. Late-maturing, thin-skinned cultivars suffer most.
- Hang red sticky spheres baited with apple essence in the tree from late June — one per 100 fruit, at head height on the outside of the canopy — and clean or replace them through the season.
- Pick up all dropped apples twice a week and remove them from the garden; the maggot is still inside and heading for your soil.
- Bag individual fruit with paper or nylon sleeves once they reach 20 mm.
- Do not compost windfalls in an open heap under the tree.
- Use damaged fruit promptly for cooking — the flesh outside the tunnels is sound.
- Remove or manage wild hawthorn and neglected apple trees within a hundred meters if you can.
- Grow early-maturing cultivars, which are often harvested before the worst of the flight.
- Keep poultry under the trees, or cultivate the surface lightly in autumn to expose pupae.
- Mow the grass under the tree short so windfalls are easy to see and gather.
- Hang the traps before the first fly appears rather than after — they are a control only if they are early.
- Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com