Lawn Grub Treatment: How to Identify and Control Lawn Grubs
Australian lawns · last reviewed
Lawn grub treatment only works if you treat the right insect at the right depth. Two very different pests get called lawn grubs in Australia. Curl grubs are the larvae of African black beetle, Argentine scarab and other beetles; they live in the soil and chew roots. Armyworm, cutworm and webworm are caterpillars that sit in the thatch and chew leaf and runners. Chlorantraniliprole — the active in both forms of Acelepryn — is registered for both, but the watering-in step is the opposite for each, so it is worth twenty minutes and a wet towel to find out which one you have before you spread anything.
How to tell if you have lawn grubs
Grub damage is regularly blamed on drought or poor soil, because the plant fails from the roots up and by the time patches show, the damage is already well underway. The symptoms split by which pest you have.
Curl grubs, feeding on the roots
- Turf feels spongy underfoot and lifts easily, like carpet.
- Patches brown off suddenly even though your watering and fertilising have not changed.
- The lawn feels loose or unstable rather than firm.
- Recovery stalls no matter what you put on it.
- Birds, wasps or other animals dig and peck the same spot over and over. They are responding to the grubs, not causing the damage.
Confirm it by lifting a section of turf, or digging at the edge of the damage, and looking for larvae in the top of the soil profile.
Armyworm, feeding on the surface
- An area that has simply stopped growing, fading out through less-healthy turf into healthy turf at the edge.
- Runners chewed back to the stolon. That one is close to conclusive.
- Nothing visible during the day — the caterpillars stay down in the thatch out of the heat.
The wet-towel test
Armyworm will not come up in the heat of the day, so give them night instead.
- Pick the edge of the damage, where the turf is still half healthy.
- Soak a towel. A sheet of heavy cardboard or thick paper works too.
- Lay it flat over the turf.
- Leave it about 20 minutes. Cool and dark underneath reads as night as far as they are concerned.
- Lift it. Grubs come up out of the thatch and start on the leaf, so you will see them on the surface.
Nothing under the towel is good news. It means the patch has another cause, and there are several worth ruling out before you reach for an insecticide — Patchy Lawns: Identifying the Causes works through them. If what you are looking at is a bleached or discoloured patch rather than physical damage, it may be a fungal disease rather than a pest — the lawn disease control guide covers Brown Patch, Dollar Spot and the other diseases LawnIQ treats for.
When grubs turn up in Australia
This is a warm-season problem. Beetle larvae are most active from spring through early autumn, and spring to early summer is the window that matters most: that is when eggs hatch and the larvae start feeding. Armyworm pressure follows heat and humidity — elevated temperatures and afternoon storms are the conditions to watch.
- Healthy lawns are targets. Warm, well-watered, fertilised turf is exactly where beetles prefer to lay. A grub problem is not evidence you have done something wrong.
- New lawns are the most exposed. Fresh fibrous shoots and a shallow root system leave nothing spare, so a new lawn is always susceptible to grub attack.
How to treat lawn grubs
The active to look for is chlorantraniliprole, which is what both forms of Acelepryn are built on — 2 g/kg in the granular, 200 g/L in the liquid. Both are described as giving up to three months of protection from a single application, and both are applied at a rate per 100 m², so the treatment starts with knowing your area.
Watering in is the step that decides it
- Root feeders (curl grubs): water in with about 6 mm immediately after applying, so the product moves down into the soil where the larvae are feeding.
- Surface feeders (armyworm, cutworm, webworm): the labels say to delay watering for 24 hours where the damage is caterpillars or visible surface feeding, so the product stays where the chewing is happening.
Apply in the evening — grubs are more active then, and the caterpillars come up out of the thatch after dark. In a heavy infestation a follow-up four to six weeks later may be needed to break the cycle.
What to apply, and at what rate
Rates below are as published on each product page. Read the label before you apply anything, and treat the label as the authority if it differs.
| Product | Active | Rate per 100 m² | What its label covers |
|---|---|---|---|
| Acelepryn GR Granular | Chlorantraniliprole 2 g/kg | 0.75–1.5 kg | Lawn grubs and surface pests including African black beetle, Argentine stem weevil, billbug, lawn armyworm, cutworm, webworm, Porina and crane fly larvae |
| Acelepryn Liquid | Chlorantraniliprole 200 g/L | 6–12 mL in water | African black beetle, Argentinian scarab, billbug, lawn armyworm, cutworm, webworm and other root- and leaf-feeding pests |
| Monarch G Granular | Fipronil 0.5 g/kg (Group 2B) | 1.5 kg Argentine stem weevil · 1.2 kg nuisance ants · 0.6 kg mole crickets | Argentine stem weevil, mole cricket, ants and ant nests in lawns, playing fields and commercial turf |
Read Monarch G's rate table rather than its shelf reputation: what it is registered for is Argentine stem weevil, mole crickets and ants. Reach for it when the damage is ant mounds or mole cricket tunnelling rather than chewed leaf — it gives fast knockdown and moves into the soil profile after watering. For armyworm and curl grub, Acelepryn is the product.
Granular goes out over dry turf with a calibrated spreader; the liquid goes through a calibrated sprayer. Calibration is the whole difference between applying the label rate and guessing at it — calibrate your spreader or calibrate your sprayer first.
Acelepryn GR Granular Lawn Insecticide
A$116.95
Acelepryn Liquid Lawn Insecticide
A$54.95
Monarch G Insecticide Granular
A$68.43
Browse all weed, pest and disease products if you are dealing with more than grubs.
How much do I need?
At the full label rate, a 4 kg bag of Acelepryn GR treats about 266 m² and the 10 kg bag about 666 m². The 100 mL bottle of Acelepryn Liquid treats about 833 m² at full rate, which covers most suburban back lawns in one bottle. At the low end of each rate range those figures roughly double.
| Area treated | Acelepryn GR | Bag | Acelepryn Liquid | Bottle |
|---|---|---|---|---|
| 100 m² | 0.75–1.5 kg | 4 kg | 6–12 mL | 100 mL |
| 200 m² | 1.5–3 kg | 4 kg | 12–24 mL | 100 mL |
| 300 m² | 2.25–4.5 kg | 10 kg | 18–36 mL | 100 mL |
| 400 m² | 3–6 kg | 10 kg | 24–48 mL | 100 mL |
| 600 m² | 4.5–9 kg | 10 kg | 36–72 mL | 100 mL |
Measure the area you are actually treating rather than the whole block, and treat past the visible edge of the damage — the grubs are already working outwards. Above roughly 600 m², the granular needs more than one 10 kg bag at full rate. If you do not know your area, the plan builder steps you through working it out.
Watch: identification and treatment
The wet-towel test, what chewed runners look like, and which product suits which situation — three minutes, out on a Queensland lawn in grub season.
Full video page, with the transcript · Lawn Grubs: The Silent Destroyers Beneath Your Turf goes deeper on what the larvae do to the root system.
Repairing the damage
Killing the grubs stops the loss; it does not put the lawn back. Once roots are chewed through the plant cannot take up water or nutrients, so drought stress bites harder, weeds move in faster and disease pressure rises. Left alone, grub damage turns into bare patches and erosion.
Where the damage is widespread, the repair is a structured reset rather than more fertiliser: soil conditioners, stimulants and slow-release fertiliser over twelve weeks, timed to rebuild the root system instead of greening up what is left of it.
Lawn planLawn Recovery PlanBefore you give up, give your lawn a second chance.Common questions
What kills lawn grubs?
Chlorantraniliprole, applied at the label rate and watered in. It is the active in Acelepryn GR (granular) and Acelepryn Liquid, and its label covers both the caterpillars that chew leaf — armyworm, cutworm, webworm — and root feeders such as African black beetle.
How long does one treatment last?
Both Acelepryn products are described as giving up to three months of protection from a single application. In a heavy infestation, a follow-up four to six weeks later may still be needed to break the cycle.
When should I treat for grubs?
Spring to early summer is the key window for beetle larvae, because that is when eggs hatch and feeding starts. Watch for armyworm through the warm, humid part of the season. Evening applications suit both.
Granular or liquid?
Pick by the gear you own and the area you are covering. The granular spreads rather than sprays, which is easier over a large lawn if you have a spreader. The liquid needs a sprayer and suits a smaller area — the 100 mL bottle is sized for a small backyard, and the 750 mL covers a lot of ground while keeping well on the shelf.
Is it safe around kids and pets?
Acelepryn GR is described as having minimal impact on beneficial insects, pets or people, and Acelepryn Liquid as low-odour, solvent-free and safe for families and pets once dry. Those are the products' own published statements — follow the directions and any re-entry instructions on the label you are holding, which is the authority.