Lawn grubs and curl grubs: spot the damage and stop them

You walk out one morning and a patch of lawn has gone a sickly straw colour overnight. You give it a tug and a whole flap of turf peels back like a loose bit of carpet — no roots holding it down. Underneath, fat little C-shaped grubs are curled up in the soil. That's curl grub damage, and the good news is it's very treatable once you know what you're looking at. This post walks you through identifying grubs, the two field tests that tell you whether you actually have a problem, the treatment options that work (with the active ingredients to look for), and when to time it all so you're hitting them when they're easiest to kill.

What lawn grubs and curl grubs actually are

"Lawn grub" gets used loosely, so it's worth being precise. The pests we're talking about here are the soil-dwelling larvae of various beetles — not the surface-feeding caterpillars (armyworm, sod webworm) that chew the leaf blades. Curl grubs live underground and eat roots.

In Australia and New Zealand these are usually the larvae of African black beetle, Argentinian scarab, and various chafer beetles. In the US the same role is played by Japanese beetle, June beetle, European chafer, and masked chafer larvae. Different beetles, same lifestyle and same fix.

How to recognise one

• Shape: A creamy white, soft body that curls into a distinct C shape when you dig it up. This curl is the giveaway and where "curl grub" comes from.
• Size: Anywhere from a few millimetres up to 40 mm depending on species and age.
• Features: A hard, orange-brown head capsule and three pairs of small legs near the front.
• Where they live: In the top 5–10 cm of soil, right in the root zone, which is exactly why the damage shows up as dead turf.

The key insight: curl grubs kill your lawn from below by eating the roots, so the patch dies and detaches from the soil. That root-severing is what makes the "loose carpet" test such a reliable diagnostic — no other common lawn problem makes the turf lift away in your hand.

The signs of damage

Grub damage is sneaky because it looks like a lot of other things — drought stress, fungal disease, dog urine. Here's what points specifically at grubs.

• Irregular dying patches: Brown or yellowing areas with no neat edges, often spreading and joining up over a few weeks. They won't green up after watering, because there are no roots to take the water up.
• Turf that lifts like loose carpet: Grab the dying grass and pull. If it peels back in a sheet with little or no root resistance, grubs have severed the roots underneath.
• Spongy, springy underfoot: The turf feels soft and bouncy because the root mat has been chewed loose from the soil.
• Birds, and animals digging: Magpies, currawongs, ibis (and in the US, skunks, raccoons and crows) tearing up your lawn are a huge tell. They're not after your grass — they're after the protein-rich grubs. Sudden bird activity is often the first warning sign.

Confirm it: the pull test and the soil-flap count

Don't treat on a hunch. Two quick checks confirm grubs and tell you whether the numbers justify spraying.

The pull test

Find a patch on the edge of healthy and dying turf. Grip the grass firmly and pull up. Healthy lawn resists; grub-damaged lawn lifts away easily because the roots are gone. If it peels back, fold it over and look at the soil surface.

The soil-flap count

This is the one that matters for deciding on treatment. You're counting grubs per area:

• Cut three sides of a 30 cm x 30 cm square (about a foot square) with a spade, roughly 8 cm deep.
• Fold the flap of turf back like opening a book.
• Sift through the top few centimetres of soil and root thatch and count every grub you find.
• Multiply by 11 to get a rough grubs-per-square-metre figure, or just compare your raw count to the table below. Check two or three spots across the affected area for a fair picture.

The treatment threshold

A few grubs in a healthy lawn is normal and not worth spraying. Treat when numbers cross the threshold below — and lower the bar if your lawn is already stressed, recently laid, or under heavy bird attack.

Treatment options

You've confirmed grubs and the count is over threshold. Here are your options, from fast-acting chemical curatives to slower biological controls.

Curative insecticides

These are what you reach for when grubs are already present and feeding. Look for these active ingredients on the label:

• Imidacloprid — a widely available neonicotinoid, very effective on young grubs. Works best applied early; less so against large, mature grubs. Granular and liquid forms exist.
• Chlorantraniliprole — lower-toxicity to bees and a long residual window, which makes it a strong choice for both prevention and early-season knockdown. Often the pick if you want one application to carry you through.
• Clothianidin or trichlorfon — trichlorfon in particular is a fast curative that hits older grubs harder when you've left it late and need a quick result.

Whatever you choose: water it in. These products have to reach the grubs in the root zone, so apply, then irrigate with 5–10 mm of water so the active moves down into the soil. Read the label for your region — registrations and brand names differ across AU, NZ and the US.

Biological options

• Beneficial nematodes (Heterorhabditis bacteriophora is the species to look for) — microscopic worms that hunt grubs in the soil and kill them. Apply to moist, warm soil in the evening or on an overcast day, since they're killed by UV and drying out. Water in well, before and after.
• Milky spore (US, Japanese beetle specific) — a soil bacterium that builds up over years. Slow to establish but long-lasting once it does.
• Healthy soil and birds — a strong, deep-rooted lawn tolerates a higher grub load, and resident birds keep numbers down naturally. Biological control is slower than chemicals but kinder to the soil ecosystem.

Seasonal timing

Timing is the single biggest lever on success. Grubs are easiest to kill when they're young and feeding near the surface — that's late summer into early autumn (roughly February–April in AU/NZ, August–September in the US), shortly after the adult beetles have laid eggs.

• Late summer / early autumn: The sweet spot. Young grubs, shallow, hungry, vulnerable. Curative products work brilliantly here.
• Winter: Grubs burrow deeper and stop feeding. Treatment is far less effective — wait.
• Spring: Large, mature grubs are tough to kill and about to pupate anyway. You may catch a second flush, but it's harder going.

If you only treat once a year, make it late summer to early autumn.

Prevention

• Keep the lawn healthy: Deep, infrequent watering and balanced feeding grow a strong root system that withstands grub feeding.
• Don't over-water in beetle season: Adult beetles are drawn to lush, moist turf to lay eggs. Easing back on watering during peak flight can reduce egg-laying.
• Watch for the adults: Beetles flying at dusk in early-to-mid summer signal egg-laying is underway — that's your cue to plan an autumn check.
• Consider a preventive application: Chlorantraniliprole applied before or around egg hatch protects through the vulnerable window if you've had grub problems before.

Frequently asked questions

How do I tell curl grubs apart from lawn caterpillars?

Curl grubs live in the soil, curl into a C, and kill the lawn from the roots up (turf lifts away). Caterpillars (armyworm, sod webworm) live in the thatch, are long and straight, and chew the leaf blades — the turf stays anchored. The fix is different, so check before you spray.

Will my lawn recover after I treat the grubs?

Lightly damaged areas usually green up once the roots regrow. Patches that lifted completely have no roots left and will need reseeding, oversowing or re-turfing once the grubs are dealt with.

Are beneficial nematodes as good as insecticide?

They can be very effective if applied correctly — moist, warm soil, no UV, watered in. They're slower and more condition-sensitive than a chemical curative, but they're a great low-toxicity option, especially for ongoing management rather than an emergency.

Why are birds tearing up my lawn?

They're eating the grubs, not the grass. Heavy, sudden bird or animal digging is one of the most reliable early signs of a grub infestation — do a soil-flap count to confirm.

How Lawnova helps you stay ahead of grubs

Lawnova builds you a lawn-care plan tuned to your grass type, your climate and your region — and it knows when curl grub season is coming. Instead of discovering damage after the patches appear, you'll get a nudge to run a soil-flap check at the right time of year, plus clear guidance on thresholds and treatment timing for where you live. Spot it early, treat it once, and skip the loose-carpet surprise.

Get your free Lawnova plan

Catch them young, water it in, and your lawn will hold its ground.