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Pasture cockchafers

There have been reports of several species of pasture cockchafers causing damage. Agronomist, David Mitchell (Landmark), reports that yellowheaded pasture cockchafers (Sericesthis harti) have been observed around Crookwell, in the Southern Tablelands of New South Wales. David reports the cockchafers have been observed in both lucerne and pasture, with concentrated ‘hot spots’ of 10-15 m in size within some paddocks. Agronomist, Daniel Withers (Elders), has reported redheaded pasture cockchafers (Adoryphorus couloni) in several pasture paddocks around Ballarat, in the Western district of Victoria. Daniel says that many paddocks have suffered extensive feeding damage, with large bare patches. Upon digging in the affected areas, anywhere between 5-10 grubs have been found per shovel. Due to the high numbers, paddocks being sown to crops this season have been cultivated, which can reduce pest populations.

The yellowheaded pasture cockchafer grub is “C” shaped, creamy-grey in colour, with 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 brown beetles about 10-15 mm in length. Redheaded pasture cockchafer adults are stout, shiny black beetles about 15mm long. Larvae are “C” shaped, whitish in colour with three pairs of yellowish legs and a hard, reddish brown head capsule. Newly hatched larvae are only 5 mm long but when mature grubs reach up to 30 mm in length. Click here for images of the yellowheaded cockchafer.

Redheaded and yellowheaded cockchafers are primarily root feeders. To check for cockchafer grubs, 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 over summer by flying, usually at dusk on warm evenings.

Control of the yellowheaded and redheaded pasture cockchafers is complicated. There are no synthetic insecticides that give effective control of yellowheaded and redheaded cockchafers because of their subterranean feeding habits. Re-sowing areas made bare by cockchafer damage using a higher seeding rate is often the most effective strategy.

Non-chemical control practices, such as sowing non-preferred pasture species (e.g. phalaris and cocksfoot) have been shown to reduce cockchafer numbers. Rotating pastures with a cereal, particularly oats, is a viable cultural control option. Experiments conducted in Western Australia have shown that treating seed with chlorpyrifos powder (0.5kg/125kg seed) can be effective, however this is only recommended in severe cases.

Predatory invertebrates and insectivorous birds also play an important role in keeping cockchafer populations in check. However, large-scale land clearing has destroyed many nesting and roosting sites of non-migratory birds and has reduced food sources for parasitic wasps. To improve biological control, existing on-farm native vegetation should be preserved, and more breeding habitats for these birds and parasitic insects should be created. Daniel reports that birds have been frequently seen in the affected paddocks around Ballarat.

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