Cockchafers

Agronomist, Mick Duncan (Northern Agriculture), reports finding a significant amount of cockchafer activity around Armidale, in the Northern Tablelands district of New South Wales. The cockchafers have been found in cocksfoot and tall fescue pastures and have destroyed large areas in several paddocks by attacking the plant roots. Mick says both yellowheaded cockchafers (Sericesthis spp.) and redheaded white grubs (Dasygnathus spp.) are commonly found in the area and may occur in mixed populations. Redheaded pasture cockchafers (Adoryphorus couloni) have been found in large numbers in a recently sown oat crop near Kilmore, in the North Central district of Victoria. The affected paddock has loamy-light clay soils and prior to this season, was a long-term pasture paddock.

Grower, Aaron Worcester, has reported a high number of blackheaded pasture cockchafers (Acrossidius tasmaniae) around Rosedale in the West and South Gippsland region of Victoria. They appear to be most prevalent across a sandy belt where many large bare or almost bare areas have been found. Aaron says 10 grubs were found in a shallow shovel full of soil and estimates there may be over 200 per square metre in the worst affected areas. Alpha-cypermethrin has been used for control and Aaron says a high number of dead grubs were found post-spraying. Agronomist, Tim Paramore (Tim Paramore Agronomic Services), has also reported blackheaded pasture cockchafers suspected of causing damage to a wheat paddock near Albury, in the South West Slopes district of New South Wales. Tim says the paddock, which was also sown to wheat in 2009, has not experienced problems with cockchafers in the past.

Cockchafer larvae are “C” shaped, creamy-grey in colour with three pairs of yellowish legs. They have hardened head capsules that vary in colour depending on species. Redheaded and yellowheaded cockchafers are primarily root feeders. Larvae of blackhead pasture cockchafers live underground in tunnels but come to the surface to feed on foliage. They typically surface at night in response to rains and heavy dews. Cockchafer larvae feed on cereals, clovers, grasses and some weeds.

Control of redheaded and yellowheaded cockchafers is complicated. There are no synthetic insecticides that provide effective control 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. Re-sowing with soil disturbance is recommended. Other control practices, such as sowing non-preferred pasture species (e.g. phalaris) 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, and should be encouraged.

For further information on yellowheaded cockchafers refer to PestFacts Issue No. 2. Click for images of blackheaded pasture cockchafers and redheaded cockchafers.