Grey false wireworm

Agronomist, Jim Cronin (Landmark), has reported grey false wireworm (Isopteron punctatissimus) attacking canola crops near Temora, in the South West Slopes of NSW. Jim says that the stems of emerging cotyledons are being ring-barked or completely severed and that 2-4 larvae can be seen on damaged plants.

The grey false wireworm, a native beetle, is an important pest of germinating canola in many parts of Victoria and southern NSW. The larvae grow to about 10 mm long and 1.5 mm wide, with a robust black-brown exoskeleton and powerful mouthparts. They have a characteristic pair of black, up-turned spines on the last segment. This species is not reported to cause damage to cereal or pulse crops; however they are an important soil dwelling pest of canola, particularly on fine textured soils.

False wireworms chew into the seedling stem and roots, weakening the plant. The injury to the seedlings makes them susceptible to dehydration and infection by disease. Feeding damage is often most severe when germination is slowed by continued dry weather. There is anecdotal evidence suggesting that stubble retention and minimum tillage are contributing to the build-up of false wireworm populations.

Grey false wireworm damage can appear as large bare patches in paddocks 3-4 weeks after sowing. In heavy infestations, major establishment failures in canola can occur. Jim reports that the damage is most severe in parts of the paddock with heavier clay soils and where the affected paddocks have been pasture for several years prior to this season. Insecticide seed dressings will be used in those areas which require re-sowing.

Early identification will prevent the extra costs of reseeding damaged areas. Chlorpyrifos is the only insecticide registered for grey false wireworm; however the broad scale application of insecticides can adversely affect non-target organisms and kill predators such as carabid beetles. Consider non-chemical options such as soil compaction, crop rotations and stubble management.