Wireworms are the larvae of click beetles. Some species live in the soil and feed on plant roots, they usually only cause problems when grassy areas are converted to vegetable beds.
Plants affected Roots of various plants
Main symptoms Roots eaten
Caused by Larvae of click beetles
Timing All year
What are wireworms?
- Wireworms are the larvae of click beetles. Some species of wireworm can be a problem vegetable gardens, especially those recently converted from grassed areas
- Of the more than 70 species of click beetle in Britain about half have larvae that are predatory and feed in dead wood, the rest develop in soil. Only a handful of those that feed in soil damage the roots of garden plants. More information on click beetles from UK Beetles
- 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 of a few species of click beetles (mostly in the genus Agriotes) can 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 click beetles can take up to four years to complete before the grubs pupate and develop into brown elongate beetles
- Wireworms are most frequent 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
- Tolerate the presence of some wireworms, low numbers won't cause much damage and in some areas of the garden such as those turfed or grassed they don't often affect plant growth
- The adult click beetles prefer to lay eggs where there is a dense vegetation cover, and so they occur in the largest numbers in 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
- Encourage predators and other natural enemies in the garden such as birds, wasps, hedgehogs and ground beetles
- 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, the nematode Heterorhabditis bacteriophora is sold as a control for wireworm. These are available from some biological control suppliers (pdf document). To be effective the nematodes need to be watered into moist soil while soil temperatures are in the range of 12-20ºC (54-68ºF). 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. The nematodes may also affect other insects in the soil and so should be used in a targeted manner.
There are currently no pesticides available to home gardeners for the treatment of soil invertebrates.
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