Wireworms
Slender, hard, yellow-brown grubs that tunnel into potatoes, carrots and seedling roots in soil that was recently grass.
Also known as: Click beetle larvae
Symptoms and identification
Small, narrow, round holes and tunnels appear in potato tubers and carrot roots, and seedlings wilt and die as their roots or stems are cut. The grubs are shiny, thin and tough, 2 to 3 cm long, and found in the soil near damaged plants.
Causes
The grubs are the larvae of click beetles. They live in soil for 2 to 5 years, particularly in grassland and weedy ground, and move up to feed when the soil is warm and moist.
Organic treatment
Bury pieces of potato or carrot on sticks as traps and remove them every few days with the grubs. Grow a mustard or other green manure to help reduce numbers.
Prevention
Avoid growing susceptible crops in newly dug turf for the first year, and dig regularly in summer to expose the grubs to birds. Lift potatoes as soon as they are mature.
Chemical treatment (use with care)
Soil insecticides are available in some countries but have limited approval in home gardens. Check local advice.