True wireworms

Consultant, Geoff Pitson, has reported grubs which have been attacking wheat crops around Temora in the south west slopes of NSW. They have been identified by Senior Technical Officer, Ken Henry (SARDI), as true wireworms. Geoff says some wheat plants have been chopped off completely below ground level, while others have had holes chewed into the underground stem. Up to 20% of the cereal plants are affected in the area.

Wireworms are the larvae of several species of Australian native beetles which are commonly called "click" beetles, coming from the family Elateridae. Click 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. 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 extensive crop damage in some areas because they feed on underground roots, seeds, and stems. They attack the 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.

True wireworm larvae tend to be less common than false wireworms in broad-acre cropping regions, although always present. They are generally associated with wetter soils than that of false wireworms, requiring high soil moisture and organic matter for survival. 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 can be distinguished from false wireworms which are hard bodied, cylindrical and fast moving. False wireworms are the larvae of another group of beetles, the Tenebrionidae.

Wireworms and false wireworms can only be controlled if they are detected in the seedbed before sowing. Insecticide can be applied to the soil with fertiliser, or seed can be treated. At this time of the year, however, control options are extremely limited. 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. Suitable crop rotations may also limit increases in population numbers.