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True wireworms

Agronomist, Elissa Strong (Walkers AGnVET Services), has reported damage to several paddocks of wheat near Forbes, in the Central West Slopes and Plains district of New South Wales. Individual tillers have been attacked at the ground level, causing some plants to wither and die. Elissa says the damage is rather patchy, with low numbers of true wireworm (Family: Elateridae) larvae found in the affected areas. The paddocks have not had a history of wireworm problems in the past.

Wireworms are the larvae of several species of Australian native beetles, and are commonly called ‘click’ beetles. The beetles are small- to medium-sized beetles with elongated, flattened bodies that have blunt rounded ends. Larvae grow to 15-40 mm, are soft-bodied, flattened and slow moving grubs. Their body colour ranges from creamy yellow in the most common species to red brown; their head is dark brown and wedge-shaped.

Wireworms cause crop damage in some areas because they feed on underground roots, seeds, and stems. They attack pre- and post-emerging seedlings of all oilseeds, grain legumes and cereals. Fine seedling crops like canola and linola are most susceptible. Most damage occurs from April to August and adults emerge in spring. It is reported that wireworm problems are often associated with stubble retention and trash from previous crops, which is believed to provide a refuge that favours survival and breeding.

Wireworms are often confused with another group of beetles called false wireworms (Family: Tenebrionidae). True wireworm larvae can be distinguished from the larvae of false wireworms by a distinct flattened, serrated dorsal plate on the tail, which has two upturned spines. Wireworms are generally associated with wetter soils than that of false wireworms; requiring high soil moisture and organic matter for survival. Elissa says the dry weather conditions and slow crop growth appear to have exacerbated the feeding damage around Forbes.

Wireworms and false wireworms can only be controlled if they are detected before sowing. Insecticides can be applied to the soil with fertiliser, or seed can be treated. Control options are extremely limited post crop-emergence. In paddocks with a history of wireworm problems, cultivation before seeding may reduce the pest pressure. This creates a hostile environment for the larvae and few are likely to survive. Rotations, including continuous cropping or short pasture phases often limit population increases.

Click here for images of true wireworms.

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