True wireworms

Agronomist, Tom Farran (West Wimmera Rural Services), has reported severe damage to a pasture paddock near Edenhope, in the Wimmera district of Victoria. Large areas of the paddock have been wiped bare and true wireworm larvae have been identified in high numbers in the affected areas. Tom says the paddock, which has a heavy (high moisture) soil type, has had a history of wireworm problems in the past. Some brassica crops around Edenhope have also recently been attacked by wireworms.  

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. 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 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.