Grey false wireworms

Seasonal conditions favours heavy infestations of grey false wireworms, particularly in the Wimmera soils of Victoria.

Where have they been reported?

False wireworm larvae, probably grey false wireworm (Isopteron spp.), have seriously damaged 10-20 ha of canola near Stawell in the Victorian Wimmera. The damaged area will probably need to be re-sown. The larvae have severed the hypocotyl of some plants just below the soil surface while chewing off cotyledons of others. The insect densities appeared to be high (about 8 larvae in a small shovel). The paddock had been burnt in March and subsequently cultivated.

Grey false wireworm habits and behaviour

The grey false wireworm, a native beetle, is an important pest of germinating canola in many parts of Victoria and southern NSW, particularly on fine textured soils high in organic matter. The species is less of a problem in cereals or pulse crops. 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 can be intensified when germination is slowed by dry weather. Anecdotal evidence suggests that stubble retention and minimum tillage contribute 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.

Our advice

Grey false wireworms often recur within the same area of a paddock from year to year. Paddocks with a history of wireworm issues that have been sown to canola should be monitored from late autumn onwards. The broad scale application of insecticides can adversely affect non-target organisms and kill predators such as carabid beetles. Consider spot spraying of pest areas or non-chemical options such as soil compaction, crop rotations and stubble management.

Control options

Chlorpyrifos is the only insecticide registered for grey false wireworm. The early identification of a problem will prevent the extra costs of reseeding damaged areas.

Description

Grey false wireworm larvae grow to about 10 mm long and 1.5 mm wide, with a robust, shiny black-brown exoskeleton with paler under parts. They have powerful mouthparts and a characteristic pair of black, up-turned spines on the last body segment.

 

* Source of field reports of grey false wireworm

Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)