Redheaded pasture cockchafers

Agronomist, Matt Mahoney (PGG Wrightson Seeds), has reported high numbers of redheaded pasture cockchafers in a pasture paddock southeast of Mansfield, in the Northeast district of Victoria. Matt says up to 6 larvae are present under a single clump of ryegrass. The paddock is a perennial pasture, containing a mixture of ryegrass, cocksfoot, sub clover and other brome grass species. The ryegrass roots are being completely pruned, and Matt reports being able to easily pull out whole plants. In the worst affected areas, only the cocksfoot & subclover are surviving. We have also received a report of cockchafers causing some issues in a paddock that was previously an old lucerne stand, near Lockhart in the Riverina district of New South Wales.

Redheaded pasture cockchafer (Adoryphorus coulonii) grubs are ‘C’ shaped, have a red-brown head capsule and grow up to 30 mm in length. They are primarily root feeders and most damaging to shallow-rooted plants such as ryegrasses, subclovers and barley grass. Adults are stout, shiny black beetles and are approximately 15 mm long. Redheaded pasture cockchafers differ from other scarabs; they have a two-year lifecycle. In some instances this may mean damage only occurs every second year, however overlapping populations are often present meaning damage can still occur every year.

In autumn, increased soil moisture stimulates grubs to move closer to the soil surface to feed on plant roots. In severe cases where populations are high, pasture becomes patchy and can be rolled back like a carpet. Damage is typically most serious from March to June. Low soil temperatures over the winter period slow down feeding activity. To check paddocks for cockchafers, dig in the affected areas. Crops sown into long-term pasture paddocks are vulnerable to attack.

Refer to PestFacts Issue No. 1 for further information on redheaded pasture cockchafers.