Wireworms
Agriotes spp.
Slender orange click-beetle larvae that tunnel into roots and tubers, worst in beds newly made from lawn. Lift maincrop potatoes early and cultivate to expose larvae to birds.
How to know it
Thin, stiff, shiny orange-brown larvae 15–25 mm long with three pairs of tiny legs at the front — unmistakable once seen, and quite unlike the fat white C-shaped grubs of chafers and weevils. The adults are the click beetles that snap into the air when turned onto their backs.
What you'll see
- Narrow round holes bored straight into potato tubers, often several per tuber.
- Carrots and beetroot tunnelled, then rotting from the wounds in store.
- Seedlings and young plants wilting and dying, with the stem eaten through below ground.
- Slim orange larvae turned up whenever the bed is forked.
- Damage worst in the first two or three years of a bed made from old grass.
Where it comes from
Click beetles lay in grassland and weedy ground in spring; the larvae live in the soil for four to five years before pupating, feeding on roots the whole time. That long larval life is why a bed dug from lawn stays wireworm-ridden for several seasons and then quietly stops being a problem.
Newly cultivated grassland, weedy plots and permanently mulched beds. Numbers fall steadily under regular cultivation and rise again if ground is left under grass or weeds.
Dealing with it
- Lift maincrop potatoes as soon as they are ready — most of the tunnelling happens in the last few weeks in the ground.
- Fork the bed over in autumn and winter and let the birds follow you down the row.
- Bury pieces of potato or carrot on skewers as traps, lifting and destroying them every few days.
- Grow salads, brassicas and legumes rather than root crops on new ground for the first few years.
- Keep the plot weed-free and cultivated; grassy ground is the nursery.
Keeping it out
- Give a bed made from lawn two or three years of cultivation before growing maincrop potatoes or carrots in it.
- Grow early potatoes, which are lifted before wireworm damage peaks.
- Avoid thick permanent mulch on infested ground for a few seasons.
- Encourage ground beetles, frogs and birds — all take wireworms readily.
- Do not leave patches of rough grass beside the vegetable beds.
What it goes for
Potatoes above all, plus carrots, beetroot, onions, brassicas, lettuce and any seedling in newly broken ground.
Trouble it brings with it
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.
- CentipedesChilopoda Flat, fast, one pair of legs to a segment — and a predator, unlike the slow round millipede it is constantly confused with. It hunts slugs, cutworms, springtails and woodlice by night under mulch and stones. Learn the difference and leave this one alone.
- Frogs & toadsAnura A resident toad works the beds every night for slugs, cutworms, and weevils. Recruit them with water — even a sunken basin pond — plus damp shade and an upturned-pot toad house; skip the slug pellets that poison their prey.
- Ground beetleCarabidae Fast, glossy night hunters that patrol the soil surface for slugs, cutworms, and root-fly larvae. Give them daytime cover — thick perennial edges, stepping stones, a log — and skip the tillage that wrecks their burrows. Grow to recruit it: Lavender,Mint,Thyme
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com