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African black beetle

Production manager, Bruce Saxton (SeedGrow), reports that African black beetles (Heteronychus arator) have been problematic around Holbrook, in the South West Slopes of New South Wales.  Bruce says considerable areas of perennial grasses have been attacked by larvae over the summer months, with many plants being completely killed. Damage to triticale has also been observed. African black beetles are normally associated with damage to long-term pastures and grasses, and some horticulture crops. Feeding damage to cereals is relatively uncommon, although there have recently been isolated reports in South Australia and Western Australia.

The African black beetle is a soil dwelling insect that favours pastures, particularly newly-sown ryegrass and also summer-dormant perennial grasses. Adults are 12 - 14 mm long, cylindrical and glossy black in colour. Larvae are ‘C’ shaped with a brown head, 3 pairs of legs and can grow up to 25 mm long. Most damage is caused by adults, which emerge in autumn to early winter. Larvae are present only from late spring to mid-summer.

Populations of beetles are known to be greater in higher rainfall areas where there has been an abundance of summer grasses. However, adult beetles can also fly into paddocks in late summer from nearby breeding areas dominated by perennial grasses.

Adults chew plants at or just beneath ground level, leaving frayed parts. Ryegrass seedlings and grasses may have roots damaged by large populations of adults and larvae. Adults either chew right through the stem or ‘ring bark’ bigger plants.

As with most other soil-dwelling pests, the African black beetle is difficult to control and insecticide sprays are often ineffective. Increasing seeding rates is a useful option in paddocks where the pest is anticipated to cause damage. If chemical control is required, spraying just prior to rain or late in the day may be better as beetles often come to the surface at night.  Bruce reports that chlorpyrifos and alpha-cypermethrin usually provide adequate control.

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