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Pasture cockchafers

Agronomist, Craig Drum (Tatyoon Rural), reports finding blackheaded pasture cockchafer grubs (Acrossidius tasmaniae) in a long-term pasture paddock southwest of Ararat, in the Western district of Victoria. Approximately 15 early instars were found in a 10 cm x 10 cm area, along with several carabid beetles. Both the adults and larvae of carabid beetles actively prey upon a variety of pests, including cockchafer grubs. Craig says the paddock will be monitored closely to determine what impact the carabid beetles (and other predators) are having on the grubs, prior to making a control decision.

Cream coloured scarabid larvae with yellow-brown head capsules have been reported by agronomist, Mick Duncan (Northern Agriculture), in an improved pasture paddock northeast of Armidale, in the Northern Tablelands district of New South Wales. These have been identified by senior technical officer, Ken Henry (SARDI), as Sericesthis spp. (yellowheaded cockchafers) and Dasygnathus spp. (redheaded white grubs). Damage was patchy and Mick says up to 50 grubs per square metre could be found in ‘hotspots’ throughout the paddock. In these areas the grass could be ‘rolled back like a carpet’.

Small, cream coloured grubs with yellow head capsules have also been reported in several newly sown crops near Forbes, in the Central West Slopes and Plains district of New South Wales. These are also likely to be yellowheaded cockchafers, or a closely related scarabid species.

Click here for images of the yellowheaded cockchafer,

Blackhead pasture cockchafers are pests of pastures and cereals in Tasmania, SA, NSW and Victoria. The grubs are creamy-grey in colour with a black head. When fully grown in winter they are about 15mm long. The grubs come to the surface at night in response to rains and heavy dews. They feed on clovers, grasses and some weeds, chewing plant material in their tunnels during the day. Small mounds of dirt surrounding holes on the soil surface are often the first sign of blackheaded pasture cockchafer activity. Other indicators are bare patches that appear in pastures from mid-autumn to late winter. Heavily infested areas may feel spongy underfoot. 

Blackheaded pasture cockchafers are the only cockchafer species that comes to the surface to feed, and several chemicals are registered for their control. Previous reports suggest that when chemicals are needed, alpha-cypermethrin generally achieves adequate control. If cockchafers are a continual problem, consider sowing tolerant pasture species such as phalaris and cocksfoot. Avoid short, open pastures and a high clover content, which favour pasture cockchafers.

Yellowheaded pasture 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 cockchafers, which come to the surface to feed, yellowheaded cockchafers are primarily root feeders.

Control of yellowheaded cockchafers is complicated; there are no insecticides that provide effective control because of their subterranean feeding habits. Pasture renovation is the key to controlling these species. 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 these 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. 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 around late November.

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