Lawn grubs are the larvae of beetles and an unwelcome garden pest. They live underneath lawns and can quickly cause severe damage to an otherwise healthy grass yard. Lawn grub larvae eat the roots of the grass, killing the lawn in the process. They also attract predators which will rummage through the grass to feast upon the lawn grubs. The result can be a patchy brown lawn at best, and at worst, a muddy, scruffy mess.
Lawn grubs do not like sunlight, and so usually stay in the soil, below the surface of the lawn. As they are not obviously visible, unfortunately it’s often the damage which is noticed before their presence is known. They are especially active during the summer when the weather is warmer, and particularly so after a wet downpour.
Thankfully, a lawn grub problem is easy to treat, and the first line of defence is vigilance. Let’s look at the different types of lawn grub, symptoms of a lawn grub infestation, and how to treat the problem.
What are lawn grubs?
Lawn grub is a general term covering two different pests: curl grubs, the larvae of beetles, which are cream with a brown head and feed on grass roots; and lawn caterpillars, such as armyworm and sod webworm, which are green, brown or striped and chew grass blades at the surface, usually at night. As they feed, both can cause lawns to weaken, discolour and die off in patches, and severe infestations can destroy large areas of turf if left untreated.
What are the types of lawn grubs?
There are many types of lawn grub which are common in Australia:
- Lawn armyworm (Spodoptera mauritia, Spodoptera frugiperda and Pseudaletia unipuncta). Predominantly dark brown/green in colour, with some patterning, and up to 5cm in length. It has a very short lifecycle which means that several generations of lawn armyworm may emerge in a year. A single moth can lay over 1,000 lawn grub eggs in 10 days, which means potentially a thousand hatched larvae looking for fresh grass to feed on!
- Sod webworm (Crambus). Light brown or dark grey with black stripes, this lawn grub reaches up to 3cm in length.
- Billbug (Sphenophorus brunnipennis). Small at up to 1cm in length, a white or cream coloured body and orange head and no legs. This one is particularly common in kikuyu grass.
A large family of very familiar grubs are those of the Scarab beetle. These are not true lawn grubs, but it useful to know about them, as they are often confused. They are distinguished from lawn grub as they have dense bodies, six legs, and have white or cream coloured bodies. They are shaped like a ‘C’, hence the nicknamed ‘curl beetle’. Curl beetles include the following species:
- African black beetle
- Argentinian scarab
- Cockchafer
- Pruinose scarab
All types of lawn grubs go through a similar lifecycle. The larvae pupate in the soil then emerge from pupation as a beetle or moth. After flying then mating, they return to the soil to lay eggs, which then hatch into a new batch of larvae. The lifecycle repeats until an outside intervention disrupts their reproduction. It’s the larval stage when most damage is done, usually from September through to March, so this is when you need to be most alert to the symptoms of lawn grubs.
What are the signs of lawn grubs on lawns?
What do lawn grubs look like?
Curl grubs are soft-bodied, cream or white larvae with brown heads. They typically curl into a “C” shape when disturbed and are found just below the soil surface, feeding on grass roots. Lawn caterpillars, such as armyworm and sod webworm, are green, brown or striped, and feed on grass leaves at the surface, usually at night.
How do you identify lawn grubs?
To confirm an infestation, inspect the lawn closely by lifting sections of turf or checking damaged areas just below the surface. You may see grubs feeding near the roots or notice extensive root damage even if grubs are not immediately visible.
What are the signs of lawn grubs?
Common signs include:
-
Brown or dead patches of lawn
-
Grass that pulls up easily like loose carpet
-
Increased bird or animal activity digging in the lawn
-
Spongy or uneven turf surface
-
Damage spreading rapidly in warm months
How do you test for lawn grubs?
Use the soapy water test to test for lawn grubs:
Step 1: Mix a bucket of water with a few tablespoons of dishwashing liquid
Step 2: Pour evenly over a 1m² section of affected lawn
Step 3: Wait 5–10 minutes
Step 4: Watch for grubs rising to the surface
If grubs appear, you have an active infestation and treatment is needed. The soapy water test is most reliable for lawn caterpillars, which it brings to the surface. For curl grubs, lift a spade-sized square of turf and check the root zone instead.
How do you kill lawn grubs?
If lawn grubs are killing your lawn, you’ll usually notice brown, patchy or rapidly thinning grass, especially in late summer or autumn. Turf that lifts easily like carpet points to curl grubs; mown-down or scalped-looking patches are more typical of armyworm. The turf often feels soft and spongy because grubs are feeding on the roots underneath. To confirm, peel back a section of lawn or perform a soapy water test to check for grubs. If present, treat immediately with Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser applied using Scotts® Broadcast Spreader for Lawn Food & Seed for an even distribution of treatment.
When should you treat lawn grubs?
The best time to treat lawn grubs is as soon as damage appears or grubs are detected, typically in late spring through early autumn when they are most active. Early treatment is more effective because grubs are closer to the surface and easier to control.
What is the best lawn grub killer?
We think that the best lawn grub killer is Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser, applied using Scotts® Broadcast Spreader for Lawn Food & Seed for an even distribution of treatment.
Chemical treatments for lawn grubs
Chemical controls provide fast knockdown of active infestations. These are best used when damage is already visible and grubs are confirmed. Always follow label instructions carefully.
Natural treatments for lawn grubs
An alternative way for killing unwanted lawn grubs is to apply Nematodes, specifically Heterorhabditis bacteriophora. This way of tackling a lawn grub problem must be timed correctly, as it acts best on newly hatched young grubs.
Preventative lawn grub control
A well maintained lawn will prevent many problems. Keep the lawn strong and healthy by regularly feeding, mowing and removing thatch, so that there are fewer appealing places for beetles and moths to lay their eggs.
How do you kill lawn grubs?
Most lawn grubs can be controlled with the same product, but timing and watering-in matter: curl grubs live in the soil, so the product needs to be watered into the root zone, while armyworm and webworm feed at the surface. The intention is to disrupt the short lawn grub lifecycle. Do check that grubs are causing the problem before treating them, as doing so unnecessarily can harm beneficial insects.
Step 1: Confirm infestation
Check symptoms and use the soapy water test.
Step 2: Choose the right treatment
Select a suitable lawn grub control product (chemical or biological depending on preference and lawn type).
Step 3: Apply evenly
Spread or spray treatment evenly across affected and surrounding areas, preferably in the evening.
Step 4: Water in thoroughly
Water immediately after application to carry the product into the root zone where grubs are feeding.
Step 5: Monitor results
Check results over the next few weeks. A follow-up treatment may be needed if pests are present in high numbers, but wait at least three weeks after the first application to see how well it has worked before applying again.
What is the Best Lawn Grub Killer?
We think that the best lawn grub killer is Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser, applied using Scotts® EasyGreen Broadcast Fertiliser Spreader for an even distribution of treatment.
Are Lawn Grub Killers Safe for Pets?
Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser is of minimal risk to pets when the instructions are followed. Apply at the recommended rate and frequency. Keep the product locked away as ingestion of large quantities can be harmful to dogs.
How do you prevent lawn grubs?
A well maintained lawn will prevent many problems. Keep the lawn strong and healthy by regularly feeding. mowing and removing thatch, so that there are less appealing places for beetles and moths to lay their eggs.
Lawn Grub FAQs
What are lawn grubs?
Lawn grubs are the larvae of beetles or moths that live in the soil and feed on grass roots. As they grow, they weaken the lawn and can cause brown, patchy damage.
What do lawn grubs look like?
Curl grubs are cream or white with a brown head and a soft curled, C-shaped body, usually found just below the soil surface. Lawn caterpillars such as armyworm and sod webworm are green, brown or striped and feed on grass blades at night.
Are lawn grubs bad for lawns?
Yes, lawn grubs can cause serious damage by feeding on the roots of turf. Severe infestations may kill sections of lawn if not treated.
How do I know if I have lawn grubs?
Common signs include brown patches, grass lifting easily like carpet, spongy turf and birds scratching or digging in the lawn.
What time of year do lawn grubs appear?
Lawn grubs are most active in warmer months, usually from spring through autumn, depending on climate and species.
Will lawn recover after grubs?
Yes, lawns can recover if treated early. Once grubs are controlled, regular watering and feeding, plus repairing damaged areas with seed or turf to suit your grass type, will help recovery. For lawns you can grow from seed, Scotts Lawn Builder™ Lawn Thickener Lawn Seed is a good option for repairs.
What kills lawn grubs fast?
Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser provides fast, effective control when applied and watered in correctly.
How long do lawn grubs last?
Lawn grub life cycles vary, but active feeding damage can last several weeks to months if untreated, especially in warm conditions.
Can you prevent lawn grubs?
Yes, healthy lawns, regular maintenance and preventative treatments during peak seasons can significantly reduce the risk of infestation.
Are lawn grub killers safe for pets?
Scotts Lawn Builder™ Lawn Grub + Insect Slow Release Fertiliser is of minimal risk to humans and animals when used as directed. Apply at the recommended rate. Store out of reach of children and pets.
