Curl grubs: signs your lawn has them and what to do
Curl grubs are the plump, C-shaped white larvae of scarab beetles — African black beetle and Argentine scarab among the pest species, native Christmas beetles among the harmless ones — and the damage they do happens underground, chewing through grass roots until a section of lawn lifts away like loose carpet. The clearest signs are brown patches that don't green up no matter how much you water, turf that peels back easily when you tug it, and magpies or ibis digging at the lawn to get at them. If you're anywhere in southern Victoria, September–October is the best window to treat preventatively, before eggs hatch into root-feeding larvae; if damage is already showing, December–February is the next best time, while the grubs are largest and easiest to kill.
One thing worth knowing before you reach for anything: not every curl grub you dig up is a problem. More on that below, because it changes how aggressively it's worth treating a lawn that's otherwise doing fine.
What exactly is a curl grub?
"Curl grub" isn't one species — it's the common name for the larval stage of several scarab beetles, all of which share the same basic look: a soft, creamy-white to pale body up to about 25 mm long, six legs clustered near the head, and a habit of curling into a tight "C" shape when disturbed. The main culprits in Victorian lawns are African black beetle and Argentine (sometimes spelt Argentinian) scarab, both introduced species whose larvae feed on grass roots through the warmer months. Native Christmas beetle larvae look almost identical and turn up in the same soil.
The adults are what you'll notice flying around outdoor lights on warm evenings from spring through summer — African black beetle adults are small, shiny and jet-black; Christmas beetles are larger, often coppery or metallic-green.
Signs your lawn has curl grubs
| Sign | What to look for |
|---|---|
| Brown, dying patches | Don't recover with watering or fertiliser; often start small and spread |
| Turf lifts like carpet | Roots have been eaten through, so a section peels back easily by hand or foot |
| Spongy or soft ground | The lawn feels loose or springy underfoot in the affected area |
| Bird activity | Magpies, ibis or currawongs pecking, digging, or leaving small holes in the lawn |
| Beetles at night | Small black or coppery beetles gathering around porch lights, mostly September–November |
Any one of these on its own could be something else — dog urine, a fungal disease, or a dry patch under a tree can all cause similar browning. It's the combination, especially turf that lifts easily and bird activity together, that points specifically to grub damage. In a buffalo lawn it's also worth ruling out other causes of yellowing before assuming grubs are to blame — our buffalo grass care guide covers how to tell grub damage apart from Buffalo Grass Yellowing and other common problems.
How to check before you treat
The soapy-water or wet-towel flush test that's often recommended for lawn grubs generally works best on surface feeders like armyworm and cutworm, which live near the top of the soil and come up quickly when irritated. Curl grubs live deeper and feed on roots rather than leaf blades, so they're less reliable to flush out this way. The more accurate check for curl grubs specifically is a small dig: cut a square of turf roughly 30 cm by 30 cm at the edge of a damaged patch, a few centimetres deep, and peel it back to look at the roots and soil underneath.
There's no widely agreed number of grubs per square metre that means "treat now" — get a feel for scale instead. A couple of isolated grubs in an otherwise thick, healthy lawn usually isn't worth spraying for. A five-minute dig turning up a grub every few centimetres, with roots visibly chewed through, is a different story and explains why the patch is dying.
Not every curl grub is a pest
Australia has well over 2,000 native scarab beetle species, and Christmas beetles are among them — their larvae live in lawns and garden beds the same way the pest species do, and there's currently no easy way for a home gardener to tell a native grub from an African black beetle or Argentine scarab larva just by looking at it. Christmas beetle numbers have declined in many parts of Australia over recent decades, largely from habitat loss, and their larvae do some genuine good in the soil — aerating it and helping break down organic matter, much like earthworms.
The practical takeaway is to treat based on how much real damage your lawn is actually showing, not on the mere presence of grubs when you dig a test patch. A lawn coping fine with a light population doesn't need spraying; one with spreading brown patches and turf lifting away does.
When curl grubs do the most damage
African black beetle, the most common lawn pest of the group, runs on roughly a one-year cycle. Adults overwinter in the soil and emerge to lay eggs from around August through to November, with a single female laying up to 80 eggs. Those eggs hatch within two to five weeks, and the young larvae start out feeding on decaying organic matter before moving on to living grass roots as they grow — meaning larvae are typically present and feeding from around October through to March. Damage is worst from December onward, once the larvae are larger and eating the most, before they pupate in late summer or autumn and emerge as the next generation of adult beetles, usually after rain.
How to treat curl grubs
Preventative treatment (September–October)
The most reliable option is a granular lawn insecticide containing chlorantraniliprole, such as Yates Grub Kill & Protect for Lawns, applied before or right at the start of egg hatching. It binds to soil and gives roughly six months of protection against curl grub and several other lawn pests. As of mid-2026, the 2.5 kg pack sells for around $69 at Bunnings and covers up to about 333 m², with a smaller 750 g pack available for smaller lawns. Water it in well straight after applying, or apply just ahead of rain, following the label rate for your lawn size.
Curative treatment (December–February)
If damage is already visible, a faster-knockdown granule containing bifenthrin, such as Richgro Lawn Beetle and Grub Killa, is aimed at actively feeding larvae rather than prevention. Water it in immediately after application, and always check the label for re-entry times for kids and pets before letting anyone back onto a treated lawn.
Organic option: beneficial nematodes
Products containing the beneficial nematode Heterorhabditis bacteriophora, sold under brands such as Nemassist, are a non-chemical alternative — they're mixed with water and applied as a drench, then work their way into the grubs in the soil. They need warm, humid soil to be effective and don't reliably persist over winter, so a fresh application is usually needed each season. Expect to pay roughly $15–$50 per application depending on lawn size and brand. Don't combine nematodes with a chemical insecticide in the same treatment window — most products that kill curl grubs will kill the nematodes too.
Whichever product you choose, follow the label. It will tell you the correct rate for your lawn size, how soon pets and kids can go back on the lawn, and whether the product needs watering in immediately or can wait for rain.
Not sure if it's curl grub damage or something else?
Regular mowing visits across the Mornington Peninsula are also a chance for us to spot problems like grub damage, fungal disease or dog urine spots early, before they spread across the lawn. Free, obligation-free quotes. Brown patches that peel back off the soil like a loose carpet, spongy turf that gives underfoot, and magpies or ibis methodically pecking at the same spots are the classic signs of curl grubs — the C-shaped white larvae of scarab beetles feeding on your lawn's roots just below the surface. Confirm it with a simple soapy water or spade test before you treat anything, since drought stress and other pests can look similar from a distance. Once you've confirmed grubs, a granular insecticide containing chlorantraniliprole applied while they're young controls them reliably, and the best window for it in Victoria is spring, not once the damage is already showing.
What are curl grubs?
Curl grubs are the larval stage of scarab beetles (family Scarabaeidae) — cream to white, with a brown head and a darker grey rear end, growing to around 25mm long and curling into a tight C-shape when disturbed. In Victorian lawns the two most common culprits are the African black beetle (Heteronychus arator), an introduced species, and the Argentine scarab (Cyclocephala signaticollis), first established in Sydney in the 1940s and now widespread across many parts of the country. Native Christmas beetle larvae can also turn up in lawns, though the adults do more damage to eucalypt foliage than the grubs do to turf. All of them live just under the surface and eat exactly the same thing: grass roots.
Signs your lawn has curl grubs
The damage curl grubs cause is root damage first, and everything else follows from that. Grass with no roots left to hold water or nutrients dies from the top down, and a lawn with no roots left to hold it to the soil comes away in your hand.
- Brown or dead patches that peel back like carpet. This is the giveaway sign — if you can lift a section of dead turf and it rolls back with almost no resistance because the roots have been chewed through, that's curl grub damage rather than drought or disease.
- Spongy, soft turf underfoot, even in patches that haven't browned off yet — a sign roots are already compromised before the surface shows it.
- Increased bird activity. Magpies, ibis and crows probing or pecking repeatedly at the same patches of lawn are often hunting grubs just under the surface, and can do a fair bit of digging damage of their own in the process.
- Grey-brown beetles or moths active at dusk from October through summer, which points to adults laying the next batch of eggs rather than an active infestation yet — worth noting the spot and treating before larvae hatch.
- Patches that look drought-stressed despite regular watering, since a lawn with damaged roots can't take up water no matter how much you give it.
How to check for curl grubs before you treat
Confirm before you spend money on treatment, because brown patches alone can just as easily mean drought stress, dog urine, fungal disease or a mowing problem. Two simple checks:
The soapy water test
Mix a few tablespoons of dish soap into a bucket of water and pour it slowly over a one-square-metre patch at the edge of a suspect area — not dead centre, since grubs there may have already moved on once the roots gave out. The soap irritates anything living in the top of the soil, and curl grubs typically surface within five to ten minutes if present.
The spade test
Dig up a section of turf roughly 30cm square and 5–10cm deep, right at the edge of a damaged patch, and count what you find. This is the more reliable check in cooler weather, since grubs sitting deeper in cold soil don't always respond to the soapy water test the way they do in warmer months.
Different Australian lawn care sources put the treatment threshold anywhere from around 10 to 25 grubs per square metre, and there isn't a single agreed number — a healthy, well-established lawn tolerates more grubs before it shows visible damage than a lawn that's already under stress from heat, shade or poor soil. If you're finding a handful and the lawn otherwise looks fine, it's reasonable to hold off and recheck in a few weeks rather than treat automatically.
When curl grubs are active in a Victorian lawn
Adult beetles emerge and fly in spring and summer, roughly October to February, mating and laying eggs in moist soil. Those eggs hatch into small larvae that feed lightly at first, then do the bulk of their root damage as they grow through summer and into autumn — peak visible damage in Victorian lawns typically shows from December through to April. As soil cools into winter, grubs move deeper and feeding slows right down, which is roughly where things sit through the middle of the year: existing grubs are dormant rather than gone, and there's little point spraying a curative treatment on inactive larvae sitting deep in cold soil. They'll be back on the move as soil warms in spring, which is exactly why spring is the treatment window that actually works — see our Victorian lawn care calendar for how curl grub treatment fits alongside fertilising, mowing and weed control through the rest of the year.
How to treat curl grubs
Chemical treatment
Granular insecticides containing chlorantraniliprole — sold in Australia as Yates Grub Kill & Protect for Lawns, and as Acelepryn-based products such as Lawn Solutions Australia's Grub Guard Ultimate — are the standard control, applied with a spreader and watered in afterwards so the granules move down to where the grubs are feeding. They work best against young larvae, so applying in spring (roughly September–December) gets far more reliable results than treating an established late-summer infestation. As of mid-2026, a 750g bag of Yates Grub Kill & Protect runs around $25 at Bunnings and treats somewhere between roughly 100m² and 330m² depending on the application rate you use — always check the current label for the exact rate on your lawn size. Always follow label directions, and keep pets and children off treated turf until it's watered in and dried, per the product label.
Beneficial nematodes (organic option)
Nematode-based products (species such as Heterorhabditis bacteriophora, sold in Australia under names including Nemassist and Ecogrow) are microscopic organisms that seek out and infect grubs in the soil, offering a chemical-free alternative. They need warm, moist soil to survive and work — generally spring through early autumn — and are less forgiving of application timing and soil moisture than a granular chemical treatment, so they suit gardeners happy to follow the product's storage and application instructions closely rather than a set-and-forget approach.
Not sure if it's grubs or something else?
We spot curl grub damage, drought stress and other lawn problems as part of our regular mowing and maintenance visits across the Mornington Peninsula, and flag anything that needs attention before it spreads. Free, obligation-free quotes.
Get my free quoteReducing curl grub damage long term
A thick, well-maintained lawn shrugs off a light grub population far better than a stressed one. Mowing at the correct height for your grass type keeps roots deeper and stronger — see our lawn mowing height guide for the right setting by grass type — and deep, infrequent watering rather than frequent shallow watering does the same. Keeping an eye out during the September–October egg-laying window is the single most useful habit, since it's the point where a preventative treatment does the most good for the least effort; our Victorian lawn care calendar lays out that timing alongside everything else worth doing month by month.
Frequently asked questions
Do all curl grubs turn into Christmas beetles?
No. Curl grub is a catch-all name for the larvae of several scarab beetles, and Australia has more than 2,000 native scarab species, including many Christmas beetles, alongside introduced pest species like African black beetle and Argentine scarab. Pest and native larvae look very similar, so it's genuinely hard to tell them apart by eye — treat based on how much real damage your lawn is showing rather than killing every grub you find.
What's the difference between a curl grub and an armyworm or cutworm?
Curl grubs are C-shaped, six-legged beetle larvae that live below the surface and feed on roots, so the damage shows as dying patches and turf that lifts like carpet. Armyworm and cutworm are moth caterpillars that feed on leaf blades at or near the surface, usually at night, and are what the soapy-water or wet-towel flush tests are really designed to bring up.
Will curl grubs go away on their own?
Eventually, but not before the damage is done. African black beetle larvae pupate and emerge as adult beetles by autumn, so the current generation does move on — but the roots they've already eaten don't recover by themselves, and a fresh batch of eggs is usually laid nearby the following spring if nothing changes.
Can I use nematodes and a chemical insecticide together?
Not in the same season, generally. Beneficial nematodes are a living organism, and most broad-spectrum lawn grub insecticides that kill curl grubs will also kill the nematodes. Pick one method per treatment window rather than combining them.
Repairing the damage once grubs are under control
Treating the grubs doesn't bring back roots that are already gone, so a badly damaged patch still needs repair once the pest is dealt with. During the lawn's active growing season — spring through early autumn for buffalo, couch and kikuyu — topdress bare patches with a lawn-grade soil mix and overseed or lay in runners depending on your grass type, then keep the area consistently moist while new growth establishes. Mowing at the correct height for your grass while it recovers matters more than usual, since scalping a thin, re-establishing patch sets it back further — our mowing height guide has the right settings by grass type, and how often to mow by season covers frequency for a lawn that's actively trying to fill back in.
Reducing the chance of curl grubs coming back
There's no way to make a lawn immune to egg-laying beetles, but a dense, healthy lawn recovers from light grub feeding far better than a thin, stressed one, and is generally less attractive to females looking for somewhere to lay. Consistent mowing at the right height and frequency, a proper spring and autumn fertilising schedule, and deep rather than shallow watering all build the kind of root system that shrugs off a small grub population instead of showing it in brown patches. A preventative granular treatment applied every spring, before eggs hatch, is the more direct option if a lawn has had a bad infestation before — it's cheaper and far less work than repairing extensive damage after the fact.
Curl grubs or something else?
It's worth ruling out the other usual suspects before you commit to a grub treatment. Lawn armyworm are caterpillars that chew grass blades from above, leaving ragged, patchy leaf damage rather than turf that peels back like carpet, and they respond to a different class of insecticide entirely. Drought stress tends to show evenly across sun-exposed areas rather than in isolated patches, and green up again once watering catches up — curl grub damage doesn't. If in doubt, the soapy water or spade test above settles it in a few minutes rather than guessing from the symptoms alone.
Frequently asked questions
What does a curl grub actually look like?
Cream to white, with a brown head and a darker, greyish rear end, growing up to about 25mm long and curling into a tight C-shape when you dig one up or disturb it. They're the larvae of scarab beetles — commonly the African black beetle or Argentine scarab in Victorian lawns — living just under the surface, feeding on grass roots.
What's the easiest way to check if I have curl grubs?
The soapy water test: mix a few tablespoons of dish soap into a bucket of water and pour it over a one-square-metre patch at the edge of a suspect area. The soap irritates anything living in the top of the soil, and grubs typically surface within five to ten minutes. You can also dig a 30cm-square patch about 5cm deep with a spade and count what turns up, which is more reliable in cold soil when grubs are less inclined to move.
How many curl grubs per square metre means I need to treat?
There's no single agreed number — different Australian lawn care sources put the action threshold anywhere from around 10 to 25 grubs per square metre, and a healthy, well-established lawn tolerates more before it shows damage than a stressed one. Visible brown patches and spongy turf are the more reliable signal that numbers have crossed into damaging territory.
When is the best time to treat curl grubs in Victoria?
September to October, before eggs hatch, is the best preventative window. If damage is already visible, December to February is the next best time, while larvae are largest, feeding hardest and easiest for an insecticide to reach. Spring, roughly September to December, when beetle eggs are hatching into small young larvae close to the surface — the easiest stage to kill before they've grown large enough to do real root damage. By the time damage is visible in late summer or autumn, the grubs are bigger, deeper and harder to control.
Will my lawn grow back after curl grub damage?
Yes, provided the roots weren't completely destroyed and you deal with the grubs first. Once they're under control, topdress and overseed or runner in bare patches during the lawn's active growing season, and keep watering consistent while new growth establishes.