Wireworms are a classic problem in new gardens and in beds that were recently lawn. You plant potatoes or carrots, and at harvest you find narrow tunnels bored through them, sometimes with a thin, hard, orange-brown grub still in residence. They are slow-developing soil pests with a multi-year life cycle, which makes them frustrating but also predictable. The good news is that the conditions that create a wireworm problem, mainly recently grassy ground, are exactly the conditions you can plan around.
How to identify wireworms
You usually find wireworms either as damage to roots and tubers or as the larvae themselves while digging.
The grub itself is distinctive: hard, shiny, and orange-brown, much firmer than a soft white grub or a cutworm. Narrow, clean tunnels into tubers and roots, especially in a bed that was lawn a year ago, are the giveaway. Compare the damage with colorado potato beetle, which defoliates potato tops rather than tunneling the tubers.
What causes wireworms
Wireworms are the larval stage of click beetles. The adults lay eggs in the soil, especially in grassy areas, and the larvae then feed on roots, seeds, and tubers for several years before maturing. Because the larvae live in the soil for a long time, a population builds up slowly and persists, and it is tied closely to grass.
The factors that favor them:
- Recently broken sod or lawn. Grass roots are wireworms' preferred food, so new beds made from lawn often start with a high population.
- Grassy weeds. Beds and edges full of grassy weeds sustain wireworms.
- Multi-year life cycle. Larvae live in the soil for several years, so a problem does not clear up in a single season.
- Susceptible root and seed crops. Potatoes, carrots, and other root and tuber crops, plus large seeds, are prime targets.
- Moist, undisturbed soil. Wireworms favor settled, moist soil where they can feed undisturbed.
How to manage wireworms
There is no easy home spray for wireworms, so management is cultural: avoid the conditions that create them, knock the population down before planting, and limit exposure of susceptible crops.
Managing wireworms
Do not plant after sod
Wait a year or two after breaking lawn or sod before growing potatoes, carrots, or other root crops in that ground. This single habit prevents most serious wireworm damage.
Keep grassy weeds down
Wireworms feed on grass roots, so controlling grassy weeds in and around beds reduces their food and their numbers.
Trap before planting
Bury pieces of cut potato or a cup of moistened seed a few inches down, mark the spots, and dig them up after several days to collect and destroy the wireworms that gather. Repeating this lowers the population before you plant.
Cultivate the soil
Working the soil before planting exposes larvae to birds, weather, and drying, and disturbs the settled conditions they prefer.
Harvest promptly
Dig potatoes and pull carrots as soon as they are ready. The longer mature roots sit in infested soil, the more wireworms tunnel into them.
There is no product fix worth recommending here for the home garden; wireworms are a soil, rotation, and timing problem, so the work is in your planning and your bait traps rather than in a bottle. The highest-leverage decision by far is simply not planting potatoes or carrots in ground that was grass last year.
How to prevent wireworms
- Wait one to two years after breaking sod before growing root and tuber crops in that ground. This is the single most effective rule.
- Rotate susceptible crops and avoid keeping potatoes or carrots in a known-infested bed.
- Control grassy weeds in and around beds to remove their food source.
- Bait-trap and cultivate before planting to detect and reduce larvae.
- Harvest root crops promptly so they spend as little time as possible in the soil.
- Plant less-susceptible crops in newly broken or known-infested ground while the population declines.
- Time plantings well. Use the planting calendar so root crops can be harvested promptly rather than left sitting in infested soil.
Which plants get wireworms
Wireworms most damage root and tuber crops and large seeds. The classic targets are potato, carrot, sweet potato, and onion, along with hollowed-out seeds and seedlings of many crops including beans and corn. Less-susceptible crops, and crops you harvest as foliage rather than roots, are a better choice for ground that was recently lawn or is known to be infested while the wireworm population declines over a season or two.
What are wireworms and what do they look like?
Wireworms are the soil-dwelling larvae of click beetles. They are slender, hard-bodied, shiny orange to brown grubs up to about an inch long, with a tough, wiry feel that sets them apart from soft white grubs. They live in the soil for several years, feeding on seeds, roots, and tubers, before maturing into the click beetles that snap and flip when placed on their backs.
Why are wireworms worse after lawn or sod?
Wireworms feed heavily on grass roots, so lawns and grassy ground build up large populations. When you convert that ground to a vegetable bed, the existing wireworms turn to your root and tuber crops. That is why the standard advice is to wait a year or two after breaking sod before planting potatoes or carrots there, and to keep grassy weeds down in the meantime.
How do I get rid of wireworms in the garden?
There is no easy home spray, so use cultural control. Avoid planting susceptible root crops in ground recently in sod, control grassy weeds, bait-trap with buried potato chunks or soaked grain to collect and destroy larvae before planting, cultivate the soil to expose them, rotate susceptible crops away from infested beds, and harvest promptly. Over a season or two of these practices and growing less-susceptible crops, the population declines.
Are potatoes with wireworm holes safe to eat?
Yes. Wireworm damage is narrow tunnels bored into the tuber. Cut away the affected channels and the rest of the potato is fine to eat. The main downside is quality and storage: tunneled tubers are blemished and can rot more easily in storage, so use damaged ones sooner rather than later.
Wireworms reward planning over reaction. Keep root and tuber crops out of recently grassy ground, control grassy weeds, bait-trap to knock back the population before planting, and harvest promptly, and you protect your potatoes, carrots, and onions from these slow, persistent soil pests.
