Wireworms

Wireworms are the larvae of click beetles. They live in the soil and feed on plant roots, they usually only cause problems when grassy areas are converted to vegetable beds.

Wireworms in potatoes  but note that slugs can cause similar damage

Wireworms in potatoes but note that slugs can cause similar damage

Quick facts

Common name Wireworms
Plants affected Roots of various plants
Main symptoms Roots eaten, holes in potato tubers
Caused by Larvae of click beetles 
Timing All year

What are wireworms?

  • Wireworms are the larvae of click beetles and they can be a problem vegetable gardens, especially those recently converted from grassed areas
  • Wireworms grow up to 25mm long and they are thin, yellowish-brown larvae that have three pairs of small legs at the head end
  • Wireworms feed on seedlings, roots and the base of stems but the main damage is to potatoes where they tunnel into the tubers. This can be confused with the damage caused by keeled slugs. Slug damage is more frequent and characterised by small openings leading to cavities in the tuber, wireworms usually tunnel straight through the potato without leaving a cavity
  • The larval stage of the click beetle can take up to four years to complete before the grubs pupate and turn into brown elongate beetles
  • Wireworms are most troublesome in newly broken ground but become much less numerous with regular cultivation, this is because the adult beetles prefer to lay eggs in grassy ground

Symptoms

  • Heavy infestations of wireworms can cause affected plants to lack vigour and they may be killed
  • Root crops such as potatoes and carrots can be tunnelled. This damage should not be confused with other soil pests such as slugs or carrot fly.

Control

Non chemical

  • The adult beetles prefer to lay eggs where there is a dense vegetation cover, and so they occur in the largest numbers in neglected, areas or where turf has been dug up to make a vegetable or flower bed. Wireworm populations will usually decline within two years following cultivation
  • Cultivation of the ground can briefly expose the grubs to predators, such as birds
  • Remove larvae of wireworms from soil as they are found.
  • A mixture of nematode species for controlling vegetable pests is sold as Fruit and Vegetable Protection and is available from some biological control suppliers (Adobe Acrobat pdf document) and may have some effect on wireworms. To be effective the nematodes need to be watered into moist soil while soil temperatures are in the range of 12-20ºC (54-68ºF) as soon as possible after purchase/delivery. These temperatures occur between April and September. Nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions. It may be necessary to water the soil before and after application to ensure the soil is sufficiently moist for nematode activity and survival. Repeat application may be necessary.

Chemical

There are currently no pesticides available to home gardeners or the treatment of soil pests.


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