Pasture cockchafers

Agronomist, Mick Duncan (Northern Agriculture), has reported observing high numbers of cockchafers in established pastures near Walcha, in the Northern Tablelands district of New South Wales. Mick says that both redheaded pasture cockchafer (Adoryphorus coulonii) and the yellowheaded cockchafer (Sericesthis spp.) larvae are present.

The paddocks are predominantly cocksfoot/tall fescue pastures, and the larvae can be easily found just below the soil surface causing damage to the roots. The larvae are attracting a large number of birds that are somewhat compounding the feeding damage by turning over grasses looking for larvae. Given the lack of reliable chemical control options, Mick has recommended over-sowing the affected areas to accelerate pasture renovation. 

Redheaded pasture cockchafer grubs are ‘C’ shaped, have a red-brown head capsule and grow up to 30 mm in length. They are primarily root feeders and most damaging to shallow-rooted plants such as ryegrasses, sub-clovers and barley grass. Adults are stout, shiny black beetles and are approximately 15 mm long. Redheaded pasture cockchafers differ from other scarabs; they have a two-year lifecycle. In some instances this may mean damage only occurs every second year, however overlapping populations are often present meaning damage can still occur every year.

Yellowheaded cockchafer grubs 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. Like redheaded pasture cockchafers, yellowheaded cockchafers are also primarily root feeders and do not come to the surface to feed. They mostly attack cereals, but will also cause economic damage to pastures.

Control of yellowheaded and redheaded pasture cockchafers is complicated. Insecticides are largely ineffective because of their subterranean feeding habits. 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. 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.