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Yellowheaded cockchafers

Agronomist, Karla Whittaker (AGnVET Services), has reported yellowheaded cockchafers (Sericesthis spp.) in a paddock containing wheat stubble near Lockhart, in the Riverina district of New South Wales. Very high numbers were observed after digging in various parts of the paddock, which will be sown to canola this year. Yellowheaded cockchafers have also been identified for agronomist, Julian Mineham (Landmark). Julian says large patches of an emerging oat crop have been badly affected near Goulburn, in the Southern Tablelands of New South Wales.

Yellowheaded cockchafer larvae are “C” shaped, creamy-grey in colour and have a yellow head capsule. When fully grown in winter they are about 25-30 mm long. The grubs live in the soil until mid-to-late summer, where they emerge as yellow-reddish beetles about 10-15 mm in length. Unlike blackheaded pasture cockchafers, which come to the surface to feed, yellowheaded cockchafers are primarily root feeders. They mostly attack cereals, but will also cause economic damage to pastures. Click here for images of yellowheaded cockchafers.

Control of yellowheaded cockchafers is complicated. Insecticides are largely ineffective because of their subterranean feeding habits, although we have received reports that suggest some level of control can be achieved with insecticides when applied to light and fluffy soils, when cockchafer larvae are close to the soil surface and if significant rain occurs soon after application causing the chemical to leach into the soil. Non-chemical options are however preferred. Re-sowing bare areas using a higher seeding rate is often the most effective strategy. Cultivating the affected areas prior to sowing a crop can also help reduce pest populations as it exposes the grubs to predation by predatory invertebrates and insectivorous birds. To help facilitate biological control, existing on-farm native vegetation should be preserved, and more breeding habitats for birds and parasitic insects should be created.

To check paddocks for cockchafers, dig in the affected areas or look on the soil surface for tunnel entrances. Crops sown into long term pasture paddocks are vulnerable to attack. Be aware that if you did not have problems with cockchafers last year, it does not mean that you won’t have this year. Adult beetles achieve long distance dispersal by flying, usually at dusk on warm evenings in late spring-early summer.

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