How to Kill Lawn Grubs & Recover from Lawn Grub Damage
We understand how heartbreaking it is for a homeowner to see their beautiful, green lawn suddenly develop ugly brown patches. You’ve put in the effort, but now your grass looks sick, feels squishy underfoot and seems to be dying off for no clear reason. If this sounds familiar, you may suspect lawn grubs, and you're right to be concerned.
A lawn grub infestation can be a serious problem, causing extensive root damage and destroying an entire lawn in just a few weeks. The good news is that with the right knowledge, you can act quickly to kill lawn grubs, repair the lawn grub damage and prevent lawn grubs from coming back. This guide will walk you through every step.
Common Signs of Lawn Grub Infestation
The first step to fixing a lawn grub problem is identifying it. Because most lawn grubs bury themselves in the soil and feed on grass roots, you often see the grub damage before you see the pests themselves.
Dead or Brown Patches
This is one of the most common signs. As the lawn grubs feed on the grass roots, the affected area can no longer absorb essential nutrients and water, causing the grass to die off. This often starts as irregular yellowing and quickly turns into dry, brown patches.
A Spongy Lawn Feeling
A lawn afflicted with curl grubs will often feel like it gives way or ‘bounces’ as you walk on it. This spongy feeling is a sign that the larvae or lawn grubs have detached the turf from its roots, leaving a layer of thatch and dying grass. In cases of severe damage, you can roll the turf back like a carpet.
Increased Bird Activity
If your lawn has turned into the neighbourhood hotspot for local magpies, butcherbirds or other feathered freeloaders to grab a quick bite, you likely have a grub problem. These birds are feasting on the fully grown larvae, which is one of their favourite snack foods.
Moths
An increase in small, greyish-brown moths flying low over your lawn at dusk is a major red flag. These are often the adult armyworm or sod webworm moths, and they are busy laying eggs to start the next cycle of feeding larvae.
Move Over Pub Test, Try These Grub Tests
Because lawn grubs bury themselves underground, you need a way to confirm your suspicions. A visual check won't work, so you'll need to force them to the soil surface.
The Wet Towel Test
An easy method is the wet hessian bag or towel test. Place a wet towel, doormat, or hessian bag on the edge of a brown patch overnight. The grubs will come to the soil's surface to feed underneath it. In the morning, lift the bag and check for larvae.
The Soapy Water Test
This is the most effective way on how to detect army worms in lawn grass. Mix a bucket of soapy water (a good squirt of dish soap will do) and pour it over a 1-square-metre area on the edge of the damaged grass. When they come into contact with soapy water, lawn grubs get irritated and come up for some ‘fresh air’. Any armyworm, sod webworm, or cut worm grubs emerge within about 10-15 minutes of pouring the mixture. It's best to do this in the late afternoon or evening when the grubs are most active.
The Usual Suspects: The Most Common Lawn Grubs Brisbane-Wide
It’s important to know which of the types of lawn grubs Australia has that you’re dealing with, as it can influence the best treatment. Homing in on lawn grubs Brisbane and South East Queenslanders commonly encounter, these are the main culprits.
Army Worm
Army worms (also called army grub or lawn armyworm) are caterpillars that are brown, khaki-green or dark grey, often with stripes, growing up to 3cm long. They are the larvae of a small, greyish-brown moth you might see flying low over the lawn at dusk.
Armyworms’ lawn damage is distinctive. They are surface feeders, munching on the grass leaf and stem. You'll notice clear brown patches that seem to move across your turf in a line, like an army. You may also find cane toads on your lawn at night, feasting on the army grubs as they come out to feed on the grass.
White Curl Grubs
White curl grubs are the C-shaped larvae of beetles, most commonly the African black beetle or Argentinian scarab. You'll find curl grubs in the soil. They have white, fleshy bodies and a brown or orange head.
These pests live entirely underground and feed on the roots of your lawn, causing extensive root damage. This leads to yellowing, brown patches, and that classic spongey lawn feeling. The grass will look like it's suffering from severe drought conditions, and a sudden increase in bird activity on your lawn is a major clue, as they are hunting the grubs.
Sod Webworm
Sod webworm larvae are caterpillars similar to army worms but are typically a lighter brown colour. The adult moths are often seen flying over the lawn, laying their eggs as they go. When the eggs hatch, the larvae develop and begin feeding.
Much like army worms, they feed on the grass leaves and can cause rapid grass grub damage. The adult moths are strongly attracted to light sources, so you may see them fluttering near your house lights at night. Their damage often appears as small, scattered dead spots that grow larger.
How to Treat Lawn Grubs
Responding after confirming an infestation requires efficiently and effectively treating lawn grubs to stop the grub-damaged lawn from deteriorating further. This is a two-part process: eradicating the current pests and then repairing your lawn.
Eradicating the Existing Lawn Grub Problem
So, how do you kill existing lawn grubs? Treatment choice can make all the difference when you’re dealing with a grub infestation. For a fast-acting insecticide to deal with feeding larvae on the surface (like armyworm), there's another option to consider: Battle Insecticide.
This product is known for its fast-acting knockdown capabilities with the active ingredient Bifenthrin. Battle Insecticide can offer more immediate results, which can be crucial in situations where grub activity is severe and rapid action is needed. Bifenthrin is also available in granular form. If you choose this option, apply to the soil, drench with water and keep off the affected area until it has dried. Proper PPE should be used when using Bifenthrin based products and it does not have sustained residual effect, meaning it’s safe for kids and pets, but it won’t prevent subsequent infestations.
Revitalising Your Grass: Grub Damage Rejuvenation Tips
After treating your lawn for grubs, it's vital to allow it some time to recover. Remove the dead leaf material with a rake to expose the soil and any extensive root damage caused. Follow up with proper watering to encourage recovery and regrowth. Watering should be done deeply and infrequently, promoting stronger root development. Now, the thought of pumping your lawn full of fertiliser might seem tempting here, but hold off a couple of weeks to allow the plant to regain a bit of strength.
Fertilising is equally important once the plant has had a moment to recover; select a high-quality lawn fertiliser such as Lawn Solutions Premium Fertiliser or Lawn kelper and apply it according to the manufacturer's instructions. When restoring areas of your lawn damaged by grubs, there's an increased risk of weed invasion.
Normally, a pre-emergent weed control product like OxaFert would be recommended. However, in scenarios where you're focusing on regrowing lost patches, using such products might impede this process. You might find it more beneficial to use a non-glyphosate weed control option, such as Bin-Die.
When the task of regrowing damaged patches becomes too challenging, or you're simply eager to see quicker results, patch repairs are an excellent solution. Purchasing a few slabs of turf in your chosen grass variety can effectively restore these areas.
How to Prevent Lawn Grubs from Coming Back
Lawn grub prevention is the best long-term strategy. Products containing active ingredients such as chlorantraniliprole are known for their effectiveness against these subterranean adversaries. One standout product is Acelepryn, renowned not only for its long-acting efficacy but also for its reduced environmental impact. This is not a knockdown spray, but a preventative, systemic insecticide. You apply it once, and it provides up to six months of year-round protection. It’s safe for bees and other beneficial insects. This is the safe and effective control method professionals use to stop future attacks before they even begin.
How to Kill Lawn Grubs and Other FAQs
When to treat lawn grubs in Australia?
The best time for preventative treatment (like Acelepryn) is in early summer or spring, just before the weather warms up and the pests lay eggs. For knockdown treatments (like Battle Insecticide), apply them as soon as you detect the grub activity, which is often in late summer or early autumn.
What does a lawn grub look like?
This depends on the type. Curl grubs (like the African Black Beetle larvae) are white, C-shaped, have six legs and a brown head, and live in the soil. Army worms and sod webworms are caterpillars that are brown, green, or grey, and live on or near the soil surface.
Can you advise on how to treat army worms in my lawn?
Once you confirm an army worm invasion, you’ll need to launch a quick counterattack. The most effective control is a fast-acting "knock-down" liquid insecticide like Battle Insecticide. For best results, apply it in the late afternoon or early evening, which is when the larvae are most active and feeding on the grass surface. If your lawn is long, a light mow the day before can help.
When applying, spray the entire affected area plus a 1-2 metre buffer zone around the visible lawn grub damage. The most important step is to always read and follow the product's label directions precisely. Unlike treatments for curl grubs, army worm sprays usually require only a light watering-in to wash the product onto the soil surface, not deep into the roots.
I used a treatment, but I still have grubs!
This can happen for a few reasons. You might have missed eggs that have since hatched, or heavy rain diluted your application. It’s important to follow the product instructions exactly, especially regarding watering it in. Some infestations of pests occur numerous times a year.
Will a well-maintained lawn prevent grubs?
A well-maintained lawn is more resilient and will recover from grub damage faster. However, even the healthiest lawns can get lawn grubs. Couch and Kikuyu varieties can be particularly susceptible to armyworm, but all lawns are at risk.
What’s the difference between a knockdown and a preventative pesticide?
This is a crucial distinction that comes down to timing the pest's life cycle.
Preventative Insecticides (like Acelepryn): This is applied before a major problem. When black beetle eggs or Argentinian scarab eggs hatch, the new larvae develop and are eliminated as they feed. Acelepryn targets pests at this early stage, stopping them from reaching the destructive third stage. It’s long-lasting and safer for non-target organisms.
Knock-Down Insecticides (like Battle/Bifenthrin): This is an emergency treatment for when the sheer numbers involved are already a serious threat. These other pesticides are fast-acting contact killers for active larvae like the stem weevil. They are essential when larvae are causing rapid damage, as it only takes two to five weeks to reach their destructive third stage. These are not for use on edible plants.
Need Help Dealing With Lawn Grubs?
For further guidance or support, feel free to contact our team at (07) 3114 8281 or drop an email to advice@jimboombaturf.com.au.
We are the preferred turf supplier in Brisbane, Ipswich, Sunshine Coast, Gold Coast, Toowoomba, and areas in NSW. You can also pop in and order in person at our sales office on 1/243 Bradman Street, Acacia Ridge. The office opens Monday to Friday 7.30am to 4pm, and Saturday 7am to 12pm.
