How do I know if I have lawn grubs?
Quick answer
Look for brown patches that keep spreading despite watering, turf that lifts easily because its roots are gone, and birds digging at the lawn. Confirm it by cutting and lifting a spade-sized piece of turf at the edge of a patch: C-shaped, cream grubs with brown heads in the root zone mean lawn grubs. Confirm before treating.
Why this happens
“Lawn grubs” usually means curl grubs, the larvae of African black beetle and other scarab beetles. They live in the soil and eat grass roots, so the damage starts underground and shows up as brown patches.
The trouble is that dry, water-repellent soil causes patches that look almost the same. Before you buy an insecticide, spend two minutes confirming what you have.
The lift test
Go to the edge of a brown patch, where the grass is still partly green. Grubs feed on living roots, so that’s where they’ll be. Cut three sides of a square about the size of a spade and fold the turf back. If grubs have been feeding, it may lift with almost no resistance because there are few roots holding it down.
Look at the roots and the top few centimetres of soil. Curl grubs are C-shaped, cream or white, with a brown head and three pairs of legs near the head. Check two or three patches and one healthy-looking area.
Grubs or armyworm?
Lawn armyworm are caterpillars, not grubs. They feed on the leaves at night, so the damage looks grazed or chewed rather than rootless, and you’ll find them in the grass at dusk, not in the soil. The treatment is different, so check which you have.
No grubs?
If the soil is dry and there are no grubs, test for water-repellent soil: pour water on the patch and watch whether it soaks in. Check your sprinkler coverage too.
If you find them
Help the lawn recover with water and a light feed. If you treat, choose an insecticide whose label lists the pest, and follow its directions exactly, including its warnings about bees and waterways.
What you may be seeing
- Brown patches that spread even though you're watering
- Turf that peels back easily at the edge of a patch
- C-shaped, cream grubs in the top few centimetres of soil
- Birds pecking and digging in the lawn
What you can do
Pick the right spotCheck first
Go to the edge of a brown patch, where the grass is still partly green. Grubs move outwards into living roots.
Lift a piece of turfCheck first
Cut three sides of a spade-sized square and fold it back like a flap.
Look in the root zoneCheck first
Look for C-shaped, cream grubs with brown heads in the roots and top few centimetres of soil.
Check a few spotsCheck first
Try two or three patches and one healthy area to see how widespread they are.
Rule out dry soilCheck first
If there are no grubs, do the water drop test for water-repellent soil.
Treat only if confirmedProduct step
Use an insecticide whose label lists lawn grubs (curl grubs or African black beetle), following its directions and bee and waterway warnings.
What not to do
- Treating every brown patch as grubs without looking.
- Applying insecticide in the middle of the day when the label says otherwise.
How much do I need?
Place straight-sided containers around the zone, run it for a set time, then measure the depth of water in each with a ruler. How to do a catch-cup test
Run time for this zone
Enter at least two cup readings, the test time and the water you want to apply.
Log it
Keep a record of what you applied, when, and at what rate. Your Lawn Journal works on this device without an account, and reminds you when the next step is due.
What's next
Related grass types, weeds, pests and diseases
Lawn problems
Related questions
Related guides
Didn't answer your question?
Ask LawnMan. We check existing answers first, and if nothing fits, your question goes on our list to answer.
Who wrote this, and what it's based on
This page hasn't been reviewed by our technical reviewer yet [CONFIRM: reviewer]. Until it is, it isn't listed in search engines. How we write and review
Sources
- Turf weed, pest and disease identification guide (poster), Bayer Environmental Science, hosted by Turf AustraliaAfrican black beetle larvae from early spring to mid summer; damage to turf roots. Accessed 3 October 2026.
- Scarabs, Business Queensland, Queensland GovernmentScarab beetle larvae. Accessed 4 October 2026.
- Native armyworm (including lawn armyworm, Spodoptera mauritia), Business Queensland, Queensland GovernmentLawn armyworm damage and monitoring. Accessed 4 October 2026.