Yellowheaded cockchafers

Agronomist, Tim McNamara (McNamara’s Country Store), reports finding yellowheaded cockchafer larvae (Sericesthis spp.) in a wheat paddock near Rutherglen, in the Northeast district of Victoria. The grubs found ranged from 5-15 mm long, and despite the high numbers (up to 8 grubs per shovel) they do not appear to have caused any damage to the crop at this stage. The crop established with excellent vigour, however, Tim says there is some concern about potential damage given the high numbers of grubs present and the lack of alternative vegetation in the paddock.

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.

There are no insecticides that provide effective control of yellowheaded cockchafers due to their subterranean feeding habits. Cultural control methods including pasture renovation, re-sowing bare areas using a higher seeding rate, and cultivating affected areas prior to sowing may be the best methods for control. Predatory invertebrates and insectivorous birds also play an important role in keeping cockchafer populations in check.

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.

Click here for images of yellowheaded cockchafers.