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.
How to know it
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.
What you'll see
- 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.
Where it comes from
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.
Dealing with it
- 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.
Keeping it out
- 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.
What it goes for
Apples and crab apples above all, then hawthorn, plums, cherries and occasionally pears.
Who hunts it for you
- 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
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com