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Consultant, Roger Garnsey (Roger Garnsey Agronomy), has observed yellowheaded cockchafers (Sericesthis spp.) in a tall fescue pasture paddock, near Holbrook, in the South West Slopes district of New South Wales. The paddock was sown about 12 months ago, and has experienced significant feeding damage this season. There has been substantial thinning of tall fescue plants. Upon digging in the affected areas Roger found up to 6 yellowheaded cockchafer larvae per shovel. Roger has also observed adult African black beetles (Heteronychus arator) that maybe contributing to the loss of plants.

Yellowheaded cockchafers are primarily root feeders and prune the roots of germinating cereals and pastures. Moisture stimulates the larvae to move closer to the surface in autumn and winter to actively feed on plant roots or decaying organic matter. Third instar larvae cause the most feeding damage to crops and pastures during winter and early spring. The African black beetle is associated with damage to long-term pastures and cereals, with the adults causing most damage in autumn-early winter when they chew the plant right through the stem at or just below the soil surface.

When both these pests are found in combination within a paddock the pressure on perennial grasses is likely to be very strong and persistence can be affected. There is little chance a chemical option will control these pests effectively due to their underground lifecycles. Sowing less favourable pasture species such as phalaris, cocksfoot or oats and cultivating the paddock prior to sowing can assist in reducing their impact.

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