Wireworms are the larvae of click beetles. They bore small round holes into tubers and make them unsaleable. Two extension services, AHDB in the UK and the University of California IPM programme, publish practical guidance with clear numbers.

A long life in the soil

The larvae live for years. According to AHDB, they feed for 4–5 years. UC IPM says common species need 3–4 years to complete their life cycle. This long cycle explains why grassland builds up populations.

The risk is highest right after grass. AHDB says crops sown within 2 years of ploughing out permanent pasture are at highest risk. UC IPM advises avoiding potatoes immediately after clover, grass, pasture or weedy alfalfa.

How to measure the risk

Low numbers can already cause damage. AHDB states that a single wireworm in 20 soil cores of 10 cm diameter can represent a significant risk. That equals about 60,000 wireworms per hectare.

UC IPM links sample numbers to field size. It uses these thresholds:

  • 10 acres (about 4 ha): 30 samples, threshold 1 wireworm.
  • 40 acres (about 16 ha): 60 samples, threshold 2 wireworms.
  • 160 acres (about 65 ha): 120 samples, threshold 5 wireworms.

Timing matters. Bait traps work when soil at 10–15 cm depth reaches about 10°C (50°F). Soil sampling should be done in spring when soil at 15 cm is 7°C (45°F) or warmer. In late summer, samples are taken at 45 cm depth, UC IPM says.

What control options exist

Chemical options are limited. UC IPM notes that the soil must be at least 10°C when ethoprop is applied. Wireworms bore up to about 1.3 cm into the tuber, but do not tunnel all the way through.

Cultural control is central. AHDB advises avoiding infested fields and considering an early harvest when damage is expected.

Why it matters

Wireworm damage is mainly a quality problem. Holed tubers can lead to rejected loads for fresh markets or processing. Both sources point to prevention through field choice and monitoring as the main tool.

Growers should sample before planting potatoes after grass. If numbers exceed thresholds, choosing another field or harvesting early usually costs less than rejected loads.

Prevention & control · Editorial note

Wireworms (Agriotes spp.): what growers can do

  • Prevention: avoid potatoes in the first two years after grassland, cultivate the soil in late summer and lift the crop as soon as it is mature.
  • Monitoring: use bait traps or soil samples before planting to estimate the risk.
  • Chemical protection: imidacloprid (IRAC 4A) and fipronil (IRAC 2B) are used as tuber or furrow treatments in some countries — check the national register of your country. They are not approved in the EU and the UK.
  • Resistance management: do not use the same IRAC group on seed tubers and on the crop in one season.

This note is provided by the potatoes.news editorial team for information only. It is not a recommendation of any company and is not mandatory. Use only plant protection products authorised in your country and follow the label. Product names and registrations differ between countries; consult a local agronomist.

Photo: Click beetle larvae (wireworms) (illustrative). ZATRIPPIT / Wikimedia Commons, public domain