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CURL GRUBS AND LAWN DAMAGE

So-called ‘curl grubs’ can wreak havoc with a well maintained lawn, leading to unsightly damage that requires professional attention in order to be rectified. 

Scarab (beetle) pests are a common lawn pest in Australia. Often called lawn grubs or curl grubs (because of the shape of their larvae), it is the larval stages of the beetles, especially the larger, later instars, that cause the most plant damage.

Most of the species eat decaying organic matter, also eating grass roots on occasions or damaging the roots whilst foraging. When present in significant numbers, the damage to the root system can be significant, such that whole areas of turf can be peeled back. Irregular discoloured areas of turf is a key indicator of their presence, which becomes more apparent under dry conditions. Birds digging up the turf to find these tasty morsels will exacerbate the damage.

There are five common pest scarab species in Australia.

African black beetle (Heteronychus arator)

A native to South Africa, the African black beetle (main picture above, image credit Paul Venter) is found primarily in coastal areas from southwestern WA around to the east coast and north into Queensland. In most areas, there is one life-cycle per year with the adults emerging in spring and summer, although it is believed there could be more than one life-cycle in warmer regions.

Turf affected: most varieties.

Scarab larva are often called curl grubs. The species can be identified by their raster – an arrangement of hairs near their anal opening

Argentinian scarab (Cyclocephala signaticollis)

The Argentinian scarab is an introduced pest found mainly in the southeastern coastal areas of Australia, up to southern Queensland. It has a one-year life-cycle with the adults emerging in summer.

Turf affected: most warm season varieties.

Argentinian scarab (Cyclocephala signaticollis)

Redheaded cockchafer (Adoryphorus couloni)

Redheaded cockchafers are a problem in the southern states from northern Tasmania into the tablelands of NSW – any area where there is rainfall in excess of 500 mm per year. This species is a little different from many other common scarab pests in that it has a two-year life-cycle. The adults emerge in early spring, with the larvae pupating around 15 months later. However, these emerging adults will remain in the soil until the following spring.

Turf affected: most cool season varieties.

Redheaded cockchafer (Adoryphonus couloni).Photo credit: JJ Harrison

Blackheaded cockchafer (Aphodius tasmaniae)

Blackheaded cockchafers are found in the southeastern states from South Australia to New South Wales and in Tasmania. It has a one-year life-cycle, with the adults emerging in summer. Their feeding pattern is different to the other scarab pests. Although the immature larvae feed in the soil on decaying organic matter, from autumn until spring, the growing larvae emerge at night to feed on turf, which they take back into their burrows. Small mounds of soil will surround burrows and the damage can become widespread over time.

The adult blackheaded cockchafer is similar in colour to the redheaded cockchafer. The cockchafers get their names from the head colour of their larvae, with the redheaded cockchafer having a red/brown head and the blackheaded cockchafer having a black head.

Turf affected: all turf types but mainly cool season varieties.

Pruinose scarab (Sericesthis germinate)

The pruinose scarab is a scarab native to the east coast of Australia from Victoria up to Queensland. With a one- year life-cycle, the adults emerge in early spring with large numbers often following warm, dry winters. The adult beetle is similar in appearance to the Argentinian scarab, although lacks the dark body markings common on Argentinian scarabs, and has small club-like antennae.

Turf affected: most varieties, but more commonly warm season turf.

Scarab populations can cause significant damage both directly on the grass roots and through birds searching for the larvae

Treatments for scarab pests are most successful when targeting the larval stages. Ideally, treatments should be timed when the larvae are small, as they are easier to kill at this stage. However, this requires turf inspections to see whether they are present (as damage is often not visible with immature larvae).

In the home lawn situation, it is more common that a treatment takes place when visible damage is obvious and later instar (mature larvae stages) are present. A range of non-repellent and pyrethroid insecticides are available for the various scarabs. Typically the pyrethroid products are more commonly used to control adults and the non-repellent chemistries are more effective on the larvae, with higher label rate applications often advised if targeting the later instar larvae. As the larvae are further down in the soil profile during this time, watering in the treatment after application will deliver the best results.