Bronzed field beetles

Agronomist, Warwick Nightingale (Delta Agribusiness), has found small beetle larvae in a seedling canola crop near Lockhart, in the Riverina district of New South Wales. These have been identified as the bronzed field beetle (Adelium brevicorne). Despite the beetles being relatively easy to find in the paddock, there has been no feeding damage observed. The crop has been sown into a brown manure pea stubble, and Warwick says there is a high amount of organic matter, which may be favouring the survival of beetles.

Bronzed field beetles are up to 11 mm long and shiny black in colour with a slight bronze appearance. The larvae are dark brown, up to 12 mm in length and 3 mm wide. They have twelve body segments, the last one having two distinct upturned spines. The larvae are often confused with the grey false wireworm, which is a serious pest in parts of southern New South Wales and Victoria.

Bronzed field beetles attack canola, but typically do not affect cereal and pulse crops. Most issues occur when canola crops are sown into heavy stubble. The larvae damage plants by chewing on seedlings at or above ground level, and will also feed on plant roots. However, larvae can be present in the soil with little or no damage to plant seedlings. This is because they also feed on dead organic matter and high numbers are required to cause serious crop damage. Larvae are typically found within the top 1 cm of the soil and can be found under plant material, clods of soil, rocks or wood.

To check paddocks for bronzed field beetles, place refuges such as terracotta tiles or carpet squares, in areas of high stubble or where previous damage has occurred. Leave these refuges in the paddock for several days before checking and counting the number of beetles present underneath.