Cockchafers and African black beetle in canola and pastures

Cockchafer larvae and African black beetle adults, collectively known as scarabs, are causing considerable damage in pastures and emerging canola

Where have they been reported?

Reports of scarab larvae (cockchafers) and adults (beetles) causing severe damage have been unusually common in the past fortnight.

Cockchafers:  Either redheaded pasture cockchafer (Adoryphorus coulonii) or yellowheaded cockchafer (Sericesthis spp.) larvae damage has been reported in emerging canola and pastures. In the Lockhart region of the NSW Riverina, a heavy infestation of cockchafers has destroyed 95% of canola that was direct-drilled into old lucerne pasture. While south of Cowra in the NSW Central Tablelands, a population of approximately 5/m²  has been reported in a 70 ha crop of emerging canola. Also in the NSW Central Tablelands, a heavy infestation has caused severe damage in multiple paddocks of perennial grass pastures near Oberon. Typical of severe infestations, birds had been ripping up plants looking for the scarabs in the most severely affected paddocks. Further south near Beaufort, Central Victoria, exceptionally high densities (approximately 30/spade) of redheaded pasture cockchafers have been reported in both free draining and heavy soils across a 300-acre weedy paddock. 

African black beetle: An aggressive population of African black beetle (Heteronychus aratoris) adults has been observed in pasture paddocks east of Warranambool in South West Victoria. The beetles appear to be preferentially feeding on established phalaris but are also chewing endophyte ryegrass seedlings and stems at the soil surface level. Endophyte ryegrass is typically resistant to black beetles, however, as the endophyte fungus can take time to express itself, emerging ryegrass can still be at risk.

About scarab pests

Cockchafers: The yellowheaded and redheaded pasture cockchafers are creamy-grey and grow up to 30 mm long as larvae. Both their head colour, and their anal opening can help to distinguish between the two. The yellowheaded cockchafer has a ‘Y’- shaped groove at its rear end and yellow head colour. The redheaded pasture cockchafer has an open, horizontal groove at its rear end and red head colour. Both cockchafers are root feeders and do not come to the surface to feed, and are thus are not readily controlled with surface-applied insecticide. Redheaded pasture cockchafers commonly attack pasture, especially those with high clover content, and occasionally wheat. They tend to lay eggs in dry pasture residue in the previous spring. Yellowheaded cockchafers primarily damage cereal crops, but also pastures.

Larvae of the yellowheaded cockchafer (left) and redheaded pasture cockchafer (right) (Source: cesar)

 

African black beetle: Adult African black beetles are shiny black, slow moving and are approximately 12-14 mm long. The wing covers have lightly indented longitudinal striations. African black beetle damage is commonly found in pasture grasses, but cereal crops including wheat, barley and triticale are also at risk. Both adults and larvae are capable of causing damage, but it is the adults that are most active at the moment. Adults chew plants at or just beneath ground level and may chew right through the stem or cause ‘ring barking’ on larger plants; larvae prune or completely sever roots.  

Adult African black beetle showing indented striations on wing covers (Source: Melina Miles)  

Our advice

Poncho® Plus seed dressing is registered against both African black beetle and yellowheaded cockchafer in pastures. This can offer control for 3-4 weeks after sowing, but will not protect seedlings from heavy pest populations.

Chlorpyrifos is registered against African black beetle in maize in NSW, however, no other foliar insecticides are registered for its control in broadacre crops. There are no synthetic insecticides registered for the redheaded pasture cockchafer.

There are a range of cultural control methods for managing these pest beetles including intensive grazing, cultivation, higher seeding rates and sowing less favourable species. For instance, oats, cocksfoot, tall fescue and lucerne are thought to be less susceptible to redheaded pasture cockchafer damage. If practical, rolling of the infested pasture can be beneficial since this helps the sward re-establish contact with the soil, and reduces activity of the larvae.

For more detailed information about these pests, and for further advice on preventative strategies, go to African black beetle, redheaded pasture cockchafer or yellowheaded cockchafer within the PestNote series. 

 

Source of field reports of scarabs

Matthew Carracher – Agronomist, PGG Wrightson Seeds (South West

Victoria)

Karl Drever – Agronomist, Davies and Rose (Central Victoria)

Christine Haigh – Grower (Central Tablelands NSW)

Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)

Peter Watt – Senior agronomist, Elders (Central Tablelands NSW)