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Vegetable beetle

Vegetable beetles (Gonocephalum sp.) have been identified for agronomist, Jim Cronin (Landmark), from a late-tillering wheat crop at Forbes, in the Central West Slopes and Plains district of New South Wales. They are in high numbers in the paddock, which has self-mulching grey/black soil and quite a strong insecticide history. Jim says they do not appear to be damaging the crop at this stage. Vegetable beetles generally feed on decaying organic matter, however in some situations they turn their attention to feeding on plants and can cause extensive damage to crops when present in high numbers. Typical damage includes chewing seedlings at or above ground level, ring barking plants or completely cutting stems.

In recent years there has been an increase in reports of vegetable beetles attacking crop plants in many regions of south-eastern Australia. It is unclear exactly what has triggered this increase although it may be related to dry periods in early winter. High populations (> 100 per m²) can often be associated with patches of previously high plant residues. Factors including temperatures > 20°C, moisture stressed crops, and light, dry soils have been associated with cases where vegetable beetles have been found attacking crops.

Vegetable beetles (sometimes referred to as ‘false wireworms’) have one generation per year, with adults emerging in spring. Common species are 6 – 10 mm long, and have a dark grey-black coloured body, which is oval-shaped and often covered in soil. Larvae are elongated, hard-bodied, cream, yellow or tan in colour, with three pairs of legs just behind the head. The body is cylindrical and up to 20 mm long.

Click here for images of vegetable beetles.

Controlling vegetable beetles is difficult as they can tolerate high rates of many insecticides. Cultural methods such as suitable crop rotations and clean cultivation over summer may be the best means of preventing the build-up of both adults and larvae in problem areas. 

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