Heteronychus arator

Other common names:

White curl grub, scarab beetle larvae, lawn beetle larvae or cockchafer.

White curl grub is sometimes incorrectly referred to as ‘lawn grub’ and ‘witchety grub’. ‘Lawn grub’ is a colloquial term for surface dwelling caterpillars such as sod webworm, army worm and cutworm, which become moths. The true witchety grub is the wood-feeding larva of two families of giant Australian moth.

Description:

White curl grubs have a characteristic ‘C’ shape and three pairs of legs (as shown in the images). They live underground, protected by soil. In subtropical areas, lawn injury is commonly seen from November through to January. The most common causal agent is African black beetle (Heteronychus arator), although a number of native and non-native scarabs that look similar and produce comparable damage. These include pruinose scarab (Sericesthis geminata) and Argentine scarab (Cyclocephala signaticollis).

Third instar African black beetle larvae grow to 20–25 mm in length before pupating in the soil. They have an orange-brown head capsule. Oval shaped, shiny black adults, 12–15 mm long, emerge during February, feeding on stems just below ground level. They are less active through winter and mate in spring after the female has reached sexual maturity.  

The late second instar and third instar phases of the beetle’s lifecycle are the most damaging to turf. These larger larvae are voracious feeders on roots and underground stems. The adults also feed on turf, but cause much less damage. What often differentiates white curl grub damage from other types of lawn dieback, such as that caused by drought or water repellent soils, is that the lawn starts to slip or roll up like a carpet. If few larvae are present, healthy turf is likely to outgrow the minor damage it will sustain. Under heat and drought stress, the problem may be exacerbated by poor rates of regrowth and smaller numbers of larvae can cause significant damage (Carson, no date).

Only one generation is produced each year. Deceptively, different larval stages are sometimes found in the soil. This is mainly due to eggs being laid at different times.

Control options:

• Pesticides: See available tabs below for registered products. Use as per label instructions.
• Integrated Pest Management (IPM):
  • Birds can control the pest; however significant damage to the turf surface is incurred by the bird(s) feeding.
  • Some white curl grubs are parasitised by the yellow (hairy) flower wasp (Campsomeris tasmaniensis) in southern Queensland. This 30 mm long hairy wasp with yellow and black banding on its abdomen can also act as an indicator of the presence of beetle larvae.
  • An entomopathogenic nematode (EN) Steinenema carpocapsae is available commercially for use in turf in Australia.  This species is an effective biological control agent against curl grub, when treatments are correctly administered.
  • Use a combination of approaches listed on this page.
• Cultural: Avoid using excessive nitrogen fertilisers and opt to use slow release turf fertilisers.
• Mechanical: Reduce thatch levels reducing favourable feeding and living conditions.

Disclaimer:

Turf Finder or its developer accepts with no responsibility for any consequences whatsoever resulting from the use of any information or product(s) listed herein. Products are to be applied as per label instructions.