Lawn Grubs & Pests in Melbourne: Identification & Treatment
Short answer: The three lawn pests that damage Melbourne lawns are armyworm (and the similar sod webworm), African black beetle larvae (curl grubs), and lawn armyworm in late summer/autumn. Signs are sudden browning, bare patches, birds feeding on the lawn, and moths at night. Act fast — a bad infestation can destroy a lawn in days. Confirm the pest, then treat with the right method at the right time.
There are few things more disheartening in gardening than watching a green lawn turn brown and patchy almost overnight. In Melbourne, late summer and autumn are when lawn pests do their worst — and because they work fast, knowing how to identify and respond quickly makes the difference between a quick recovery and a lawn you have to re-lay.
This guide covers the pests we actually see across the northern suburbs, how to identify them, and the safe, effective treatment options.
The main culprits in Melbourne lawns
1. Armyworm (and sod webworm)
The most destructive and the most common cause of "lawn disappeared overnight" calls.
- What they are: smooth-bodied caterpillars, around 25–40 mm long, often greenish-brown with stripes. Sod webworm are the larvae of the small moths you see flitting over the lawn at dusk.
- What they do: chew through grass leaves and stems at night. A heavy infestation can strip a lawn back to bare soil in 2–3 days.
- When: late summer to autumn (Jan–April) is peak. They're called "armyworm" because they march across the lawn in a front, devouring as they go.
- Signs: sudden brown patches that spread rapidly; ragged, chewed leaf blades; small green or black droppings (frass) on the soil; moths flying up when you walk across the lawn at dusk; flocks of birds feeding intensively on the lawn.
2. African black beetle (and curl grubs)
- What they are: the adult is a shiny black beetle ~12 mm long. The larvae are white curl grubs — C-shaped, cream-coloured with a brown head, up to 30 mm.
- What they do: the larvae eat grass roots just below the surface. Affected lawn lifts up like loose carpet (roots are gone) and browns off in irregular patches.
- When: grubs are most active in summer and autumn.
- Signs: lawn feels spongy; patches lift easily when pulled; birds (especially magpies and ibis) digging in the lawn; you can find the grubs in the soil under damaged patches.
- Note: some beetles and grubs in the lawn are harmless or even beneficial. Only treat if damage is occurring — presence alone isn't a reason to spray.
3. Billbug (weevil larvae)
- What they are: larvae of a small weevil; small, legless, white grubs with a brown head, inside the stems and crown of the grass.
- Signs: small round dead patches that slowly enlarge; stems easily pull away from the crown; fine "sawdust" (frass) at the base of stems.
- Often mistaken for drought or disease — if a patch isn't responding to water, suspect billbug.
4. Two-spined mite and other sap-suckers
Occasionally cause yellowing or stippling of leaf blades. Usually secondary to a stressed lawn. Improve lawn health and they usually resolve.
How to confirm which pest you have
Before treating, identify. Different pests need different controls and treating for the wrong one wastes money and can harm beneficial insects.
- The soapy-water flush (for caterpillars and grubs near the surface): mix a few squirts of dishwashing liquid in a bucket of water and pour over a 1 m² patch of the affected (edge of the damage, not dead centre) lawn. Wait 10 minutes. Pests will come to the surface to escape the soap. Caterpillars, grubs and weevil larvae will be visible.
- Peel back the turf (for curl grubs): at the edge of a damaged patch, grab the grass and lift. If it peels up easily and you find C-shaped white grubs in the soil, it's African black beetle larvae.
- Inspect stems (for billbug): pull on affected stems. If they break away from the base easily and you see fine sawdust, suspect billbug.
- Look at night with a torch (for armyworm): they feed at night. You'll often see them on the leaf blades after dark.
Treatment options
For armyworm and sod webworm (caterpillars)
These are the most urgent — act the day you confirm them.
Biological / low-toxicity (try first):
- Bacillus thuringiensis (Bt) — a naturally occurring bacterium that kills caterpillars but is safe for birds, pets, people and most beneficial insects. Available as a spray. Best applied in the evening (sun breaks it down) and repeat after 7 days.
- Spinosad — another low-toxicity biological option effective on caterpillars.
Chemical (if biological fails or infestation is severe):
- A registered lawn-grub or caterpillar insecticide (active ingredients such as chlorantraniliprole or beta-cyfluthrin). Apply in the late afternoon/evening because the grubs feed at night, and don't mow for a couple of days before/after so there's leaf to absorb the spray. Always follow the label.
After treatment: fertilise lightly and water well to help the lawn recover and regrow into the damaged patches.
For curl grubs (African black beetle larvae)
Biological:
- Beneficial nemodes (Heterorhabditis species) — microscopic worms that hunt and kill curl grubs. Applied as a soil drench, safe for everything except the grubs. Best in warm soil (spring–autumn) and needs moist soil to work.
Chemical:
- Registered lawn beetle/grub products. Apply in spring when larvae are small and near the surface — they're much harder to kill once mature. Water in thoroughly so the product reaches the root zone.
For billbug
Systemic insecticides (taken up by the plant and killing the larvae inside the stems) are usually needed. Timing matters — early detection is key. Improve lawn health to help it outgrow light damage.
General principles of safe pest control
- Confirm before you treat. Misdiagnosis is the most common (and most expensive) mistake.
- Try the least-toxic option first. Bt and beneficial nematodes are remarkably effective and don't kill the bees, ladybirds and earthworms that keep your lawn healthy.
- Follow the label exactly. Don't increase the dose, don't spray in wind or rain, and respect the withholding period (time before kids/pets should go on the lawn).
- Spot-treat where possible rather than blanket-spraying the whole yard.
- Don't spray flowering weeds or flowering lawn (clover in flower) — bees. Mow flowers off before treating or avoid treating flowering areas.
- Time it right. Caterpillars: evening. Curl grubs: spring, watered in deeply.
Prevention: a healthy lawn resists pests
Pests target stressed lawns. The best long-term defence is a thick, healthy sward:
- Feed and water appropriately (see our lawn care guide and fertilising guide).
- Mow at the right height — not scalped.
- Aerate compacted soil so roots are strong.
- Monitor in late summer — check for moths at dusk and look for early browning. Early catch is everything.
- Encourage birds — magpies, ibis and plovers eat huge numbers of grubs. A bird-friendly garden is free pest control.
Recovery after damage
If pests got ahead of you:
- Confirm they're gone (re-check with the soapy flush a week after treatment).
- Rake out dead, loose grass.
- Top-dress low/bare areas with a sandy lawn soil.
- Fertilise with a balanced feed to push regrowth.
- Water well and keep traffic off while it recovers.
- For large bare patches, sow seed or lay new turf in the appropriate season.
A warm-season lawn (Buffalo, Kikuyu, Couch) will usually runners back across bare patches within a few weeks if it's healthy and the grubs are gone.
Want help diagnosing or treating?
If you're not sure what's hitting your lawn, send us a photo — or we'll come and take a look. Misdiagnosing is the most common mistake and the most expensive; it's worth getting right.
Garden MC provides lawn care across Meadow Heights, Greenvale, Roxburgh Park, Coolaroo, Westmeadows, Attwood, Dallas, Campbellfield, Fawkner, Gladstone Park, Jacana, Mickleham, Broadmeadows and Tullamarine. Free quotes: 0448 215 297.
FAQ
How do I know if I have lawn grubs?
Look for sudden browning or bare patches, ragged chewed leaf blades, moths flying over the lawn at dusk, birds (especially magpies and ibis) digging in the grass, or a lawn that lifts up like loose carpet. Confirm with the soapy-water flush test.
What is the best treatment for armyworm in lawns?
Bt (Bacillus thuringiensis) is a safe, effective biological spray for caterpillars — apply in the evening. For severe infestations, a registered lawn-grub insecticide applied at dusk works fast. Act quickly; armyworm can destroy a lawn in days.
Are lawn grubs harmful to pets or kids?
The grubs themselves are harmless to touch. However, the insecticides used to treat them can be — always follow the label, respect withholding periods, and keep kids and pets off until the product has been watered in and the lawn is dry.
Why are there moths flying over my lawn at night?
They're almost certainly sod webworm or armyworm moths laying eggs. A few is normal; lots, followed by browning patches within 1–2 weeks, means the caterpillars have hatched and are feeding — treat promptly.
Will my lawn recover after lawn grub damage?
Usually yes, especially warm-season grasses (Buffalo, Kikuyu, Couch), which spread by runners and will regrow into bare patches once the grubs are gone. Help it along with a light feed, water, and top-dressing of any deep bare spots.
Got a lawn problem you can't pin down? Contact Garden MC or call 0448 215 297 — we'll diagnose it and get it sorted.
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