Grey false wireworms

Agronomist, Luke Maher (AGRIvision Consultants), has reported finding grey false wireworms in a newly established safflower crop near Swan Hill, in the Mallee district of Victoria. Some chewing damage was evident on the stems of plants just below the soil surface. Although grey false wireworms are most problematic in canola, they may attack other crops if there are no alternative food sources.

Grey false wireworm (Isopteran spp.) larvae are shiny brown-grey on top and paler underneath. They grow up to 9 mm long and have two prominent upturned spines protruding from the last body segment. The adult beetles are dull grey-brown, approximately 8 mm long and do not feed on crop plants.

Although grey false wireworms are relatively widespread in south-eastern Australia, they are only a sporadic crop pest and are generally associated with cracking clays or grey clay soils. They damage crops by chewing plant stems and roots, as well as ring-barking seedlings and in some cases severing the stems completely. Seedlings can die through dehydration or disease infection, and affected areas appear as bare patches within a paddock or missing sections of crop rows. Grey false wireworms can survive in continuous cropping situations by feeding on stubble mulch when crop plants are unavailable.

Controlling false wireworms is somewhat complicated as larvae spend most of their time underground. Chlorpyrifos is registered as a foliar spray against false wireworms in certain broad-acre crops in some states. Incorporating insecticides into the soil either mechanically, or with rainfall, is reported to improve efficacy against false wireworms. Although too late for most crops this season, post-sowing compaction with a rubber tyre roller can improve seedling vigour and remove soil cracks, which will restrict the movement of grey false wireworms. Other cultural control methods include the removal of stubble from paddocks, increasing sowing rates, and sowing a less susceptible crop such as a pulse or cereal into paddocks where grey false wireworms are a known problem.