Wireworm Holes Through My Leek Shaft

At harvest, trimming a leek and finding one or more narrow, perfectly round holes bored through the shank — sometimes with the thin, orange-yellow larva still inside — is wireworm damage. Wireworms are the larvae of click beetles (Agriotes species), and they live in the soil for three to five years before pupating into adult beetles. They bore through the stems and roots of many vegetables, and the long white-to-orange, wiry-feeling grubs are unmistakeable when found in soil or plant tissue.

What wireworm looks like

Wireworm larvae are 15–25 mm long, hard-bodied, and orange-yellow or golden-brown in colour. They have a distinctly wiry or rigid feel compared to soft white grubs like chafer or vine weevil larvae. They are slow-moving and curl into a slight crescent shape when disturbed. The holes they bore through leek shanks are typically 2–3 mm in diameter, cleanly round, and may pass completely through the shank or stop part-way. Secondary bacterial rot sometimes develops inside the tunnel.

Why it is worst on new ground

Wireworm populations are highest in ground that has recently been converted from permanent or long-term grassland. Grass roots provide ideal food and habitat for click beetle larvae over many years, and populations can be very high in the first two to three years of cultivation on previously grassed ground. Regular cultivation — digging, rotovating, and general soil disturbance — exposes the larvae to birds and desiccation, reducing populations progressively. Ground that has been cultivated for five or more years typically has very low wireworm pressure.

Reducing wireworm damage

There is no approved chemical treatment for wireworms in the home garden. Practical measures include regular deep digging in autumn to expose larvae to frost and birds; leaving freshly dug soil for birds to forage through; avoiding very wet, compacted soil that provides the best wireworm habitat; and, where populations are very high, planting susceptible crops like leeks in beds further from the wireworm hotspot. Trap crops (potato pieces buried in the soil) can be used to concentrate larvae for removal, though this requires diligent checking and removal.

Are wireworm-damaged leeks edible?

Yes — trim away the tunnelled area, wash the leek thoroughly, and the rest is perfectly edible. The tunnel itself is the extent of the damage; the surrounding tissue is clean and unaffected unless secondary rot has developed inside the tunnel, in which case trim that away as well.