Vegetable beetle

Agronomist, Darren Scott (Heinrich AGPlus), has reported adult vegetable beetles (Gonocephalum spp.) causing damage to several canola paddocks around Coleraine, in the Western district of Victoria. Darren says that six paddocks in particular have been extensively damaged, while many more have suffered some level of attack.

Adult vegetable beetles attack emerging canola and spring-sown crops. They chew on stems and growing points at or above the ground. In some cases, portions or whole paddocks have had to be re-seeded following attack by vegetable beetles. Adults and larvae will also feed on decaying organic matter, and are favoured by heavy stubble or large quantities of pasture residues.

The larvae, sometimes referred to as false wireworms, are soil dwelling. They grow up to 20 mm long, are cream, yellow or tan in colour and have two upturned spines on the last body segment. They are shiny, hard-bodied, cylindrical and segmented with a rounded head. The larvae are present from autumn to spring, but are not known to cause damage to canola. They are minor pests of winter cereal crops and bore into germinating seed and chew on seedling roots and shoots.

Adults are oval, 6-8 mm long and flattened. They are usually a dull grey, but sometimes appear brown or almost black in colour. Often they have soil or sand covering their back. Adults may be abundant and are usually found under plant material, wood and rocks.

Monitoring of paddocks for larvae before sowing is important because the most effective method of control is applying a seed dressing prior to sowing. Post-sowing rolling and increased seedling density can reduce the impact of vegetable beetles at crop establishment. Vegetable beetles can be difficult to control with foliar applications of insecticides. In experiments conducted in Western Australia, it has been found that vegetable beetles are very difficult to kill using chemical sprays aimed at other species, such as vegetable weevils.