Wireworms

Identifying wireworms

Wireworms are are orange brown in colour and have long, narrow, segmented bodies with three pairs of segmented legs behind the head. This gives them a wire-like appearance, hence their name. In size they are only 1-2cm long and 1-2mm across, so are quite hard to spot in the soil. In the UK wireworms are predominantly active from March to May and September to October. They can live for up to four years.

Find wireworms on...

Wireworms may eat the roots and tubers of many different plants. The damage caused by wireworms is visible on root vegetable crops, particularly potatoes, where wireworms tunnel into the root and cause brown or black areas. However, wireworms may not be the only culprit as other creatures such as slugs or carrot root fly may have made the initial holes, and the wireworms then enter the root or tuber. If there’s only small amounts of damage, simply cut out and discard these parts when preparing food for cooking, but do not store damaged roots as they will quickly rot. Lifting root crops as soon as they are ready is a good approach, rather than leaving them in the ground where they are susceptible to attack. Seedlings that collapse and die, and plants that lack vigour due to roots being eaten, may be caused by wireworms.

How to get rid of wireworms

Plants growing in ground that has recently been brought into cultivation from lawn or grassland are most likely to be at risk so, if possible, avoid growing susceptible root crops and seedlings in new ground in the first few years. You can control wireworms naturally by regular cultivation to reduce wireworm populations. The spherical translucent eggs, 0.5 mm across, are laid in clusters just below the soil surface, so light hoeing exposes eggs to air and sunlight where they dry out, to be eaten by birds and other wildlife. Encourage birds, hedgehogs, and other creatures, which feed on the larvae.

There are no chemical pesticides suitable for gardeners to use to combat wireworms. The best product to kill wireworms is a biological control: the nematode Heterorhabditis bacteriophora. As biological controls are living organisms, applying at the right time and according to instructions is important: generally, between spring and early to mid-autumn, when soil temperatures are between 12 and 20֯C. However, be aware that this control may be unnecessarily killing other harmless soil-dwelling larvae, so only apply if there is a clear problem with wireworms.