How to Get Rid of Curl Grubs
A widespread pest, curl grubs can cause havoc to a beautiful lawn in a very short space of time. They can feast on the roots of many different plants, but are a particular problem to grass. Curl grubs are also a favourite food of birds, and considerable damage can be caused by predators keen to dig them up from beneath the surface of the lawn.
What do curl grubs turn into?
Wondering what curl grubs turn into? Curl grubs belong to the Scarabaeidae family, and when mature become recognisable as scarab beetles. There are over 30,000 different species of scarab beetle worldwide, of which over 2,000 are native to Australia. Some of the most well-known species to appear in lawns include:
- Argentinian Scarab
- African Black Beetle
- Pruinose scarab
- Redheaded cockchafer
There are other types of lawn grub which are very damaging too:
- Billbug. These look in every way like a scarab beetle larvae, except that they are smaller at maturity, and do not have legs.
- Lawn armyworm. Brown-green in colour, rather than the pale colour of a curl grub.
- Sod webworm. Darker in colour, and not typically in a ‘C’ shape unless disturbed.
It is important to get rid of any lawn and curl grub infestations as early as possible, as they can quickly destroy vast swathes of grass.
How to identify curl grubs
Curl grubs can easily be distinguished from other types of lawn grub. Curl grubs have a:
- White or cream coloured body
- Grey rear
- ‘C’ shaped chunky body
- Set of six legs
These characteristics have earned them the nicknames ‘curl grubs’ and ‘white curl grubs’.
The following species of Scarabaeidae are known to damage lawns at their larval stage:
- African black beetle (Heteronychus arator). These reach about 25mm in length, with light brown heads.
- Argentinian scarab (Cyclocephala signaticollis). The moth of this insect can lay a huge number of eggs, and hundreds of larvae may be present in a square metre. Very similar to African black beetle as larvae.
- Pasture cockchafer (Aphodius tasmaniae). Grey after hatching, but maturing to a pale cream colour with a black head.
- Pruinose scarab (Sericesthis germinate). The larvae is cream coloured, up to 20mm in length with a light-brown head. This species is native to Australia.
- Redheaded cockchafer (Adoryphorus coulonii). Light grey and small when young, but quickly growing to 30mm in length and developing a reddish head.
Although they are hard to differentiate at larval stage, as adult beetles their appearance can vary significantly.
Other types of scarab beetle larvae are less of a problem to lawns, but may attack other plants:
- Christmas beetle (Anoplognathus spp.)
- Elephant and Rhinoceros beetle (Xylotrupes ulysses)
Understanding the lifecycle of a curl grub beetle is helpful in knowing when and how to successfully treat the pest:
- Early-mid Spring (September and October). Beetles emerge from pupae. They fly, mate, and return to lay eggs in the soil.
- Late Spring & Summer (November to February). Eggs hatch, larvae emerge and feast on plant material, such as grass roots.
- Autumn & Winter (March to August). Larvae return to soil to pupate, before emerging as beetles in early Spring.
It is at the larval stage when most lawn damage is done, so be particularly vigilant from November through to February, when curl grub larvae are very active at the grass roots.
Recognising the symptoms of curl grubs
Tell-tale symptoms of curl grubs in a lawn include:
- Brown patches, where the grass is dying
- Grass which is light and spongey to walk on, where the soil has been disturbed and loosened by larvae
- Birds pecking at the lawn, to retrieve and eat the larvae
If you suspect that curl grubs are present, check for larvae in the soil by watering the ground in the evening, covering, and then checking in the morning. If curl grubs are at the surface when removing the cover, it is time to take action.
How to kill curl grubs
There are many ways to get rid of curl grubs. A synthetic curl grub killer will provide a fast solution to the problem, and can be used in granular or liquid form.
Natural ways to get rid of curl grubs include:
- Hand-picking curl grubs from the soil surface. This is a low-cost and very environmentally friendly way to control the problem. However, it is unlikely that all grubs will be found, and must be done regularly. To do this effectively, water the lawn in the evening, apply a cover, such as a piece of cardboard, and then return a few hours later or the next morning to collect them from under the covering. Dispose of them away from the garden.
- Applying nematodes. Specifically, Heterorhabditis zealandica, which will kill the grubs. These microscopic nematodes target curl grubs, entering their bodies and releasing bacteria which then feed on the grubs. Nematodes need to be used soon after purchasing, so buy them at a suitable time of year and closely follow the supplier’s instructions.
- Spraying the lawn with neem oil. This is an extract from the neem tree (Azadirachta indica), and makes the grass unpalatable to curl grubs as well as repelling adult scarab beetles.
Once the curl grub problem has been resolved, feed the lawn to help the grass recover to full strength. You may need to reseed or turf areas where damage was particularly bad.
The lifecycle of a curl grub can be anything from one to three years, depending on the species. Be alert to the problem recurring from year to year and retreat if necessary.
How to prevent curl grubs
Maintain your lawn well, by scarifying regularly to remove thatch where eggs may be laid. A healthy, vigorous lawn will be able to recover more quickly than one which is battling other problems.
Feed the lawn with a fertiliser which is suitable for your lawn type. We recommend Scotts Lawn Builder™ All Purpose Slow Release Lawn Fertiliser for most lawns, applied using Scotts® EasyGreen Broadcast Fertiliser Spreader.
Do not mow the grass too short - doing so makes it easier for adult beetles to reach the soil surface in which to lay eggs.
If laying a new lawn, use a buffalo grass variety, as it is less susceptible to curl grub damage and can recover more quickly.
Avoid lighting up a lawn in the evenings, as adult beetles will be more attracted to the garden.
Above all, monitor for indications that a curl grub problem may be brewing. Early warning can make treatment much easier.