How to get rid of lawn grubs and army worm in Australia

The lawn was fine, and then patches started dying and pulling away like carpet. If you have lawn grubs or army worm, that is the pattern. You water, you feed, and the brown patches keep spreading. Birds are tearing at the lawn early in the morning. Pull back a dying section and the roots are gone, with white C-shaped grubs sitting in the soil. Here is what is happening, and why the best time to deal with it is before you can see any of it.

What you are actually dealing with

Two different pests cause most of this damage and they work in different ways. Lawn grubs are the larvae of beetles, mainly African Black Beetle, along with Argentinian Scarab, Argentine Stem Weevil and Billbug. The adult beetles lay eggs in the lawn over late spring and summer, the eggs hatch, and the larvae live in the soil eating grass roots. Because the damage is underground at the root, the lawn above browns off, and with the roots severed, whole sections lift away like loose carpet.

Army worm and other caterpillars, including black cutworm and sod webworm, work on the surface instead. They feed on the leaf, usually at night, and can strip sections of lawn in a matter of days. Army worm damage shows as fast-moving bare patches, often in late summer, and the heavy bird activity is the giveaway. The birds are feeding on the caterpillars.

Why the damage appears so suddenly

The frustrating part of grub damage is that by the time you see it, the problem is well advanced. A grub does little visible damage while it is small. It is in the last stages of its larval life, when it is largest and feeding hardest, that the roots go and the lawn collapses. So the lawn looks healthy, then seems to fail almost overnight. It was being eaten from below the whole time.

That is also why reactive treatment is difficult. A large, late-stage larva is much harder to control than a young one, and by the time you have noticed the damage, bought a product and applied it, a good deal of the harm is already done. Chasing grubs after you can see them is always the hard way to do it.

The fix is timing, not just product

The reliable way to beat lawn grubs is to treat before they establish, not after. In most of Australia the key window is September, ahead of the peak egg hatch of African Black Beetle. A preventative application at that point puts control in the soil before the larvae are there to cause damage, so they are dealt with while they are small and vulnerable rather than large and destructive. For army worm and other caterpillars the main pressure comes later, through late summer, with March a key control point.

This is the single most important shift in how to think about grubs. You are not waiting to see a problem and then reacting. You are putting protection down ahead of the season, so the problem never reaches the visible stage in the first place.

Acelepryn, and how to use it

Acelepryn is the product for this, and it is registered for exactly these pests. It contains 200g/L chlorantraniliprole and controls both lawn grubs and army worm from a single application, with up to 6 months of residual protection at the higher rate. Once applied and watered in, it binds to the top 10 to 20mm of soil. Grubs and beetle larvae pick up the active as they burrow and feed on roots, and for army worm it releases steadily into the turf over the following months, controlling caterpillars as they feed on the leaf. It is safe on all Australian turf varieties including buffalo, couch, kikuyu and zoysia.

The rate is 8 to 15ml per 100m2 in 5 to 10L of water through a garden sprayer. Use 15ml per 100m2 for up to 6 months of protection or where pest pressure is high, and 8ml for a standard preventative pass. Water it in lightly straight after application. The one exception: if army worm are already active when you spray, leave the product on the leaf for 24 hours before watering in, so the caterpillars take it up first. One 100ml bottle treats up to 660m2 at the standard rate, so a typical suburban lawn is covered by a single bottle with product to spare.

A practical point that makes Acelepryn easy to live with: it is unscheduled and exempt from poison scheduling, needs no protective equipment, and the lawn is safe for children and pets again as soon as the spray has dried. Do not tank-mix it with your other products. Apply Acelepryn first, water it in, then run your liquid program once the surface is dry.

Complete the program

Acelepryn stops the pest. It cannot rebuild the roots and turf the grubs have already eaten. Once the grubs are controlled, recovery is the same as any root-zone recovery job: Vital to drive new root development, Surge to push the leaf growth that fills the damage back in, and the soil layer underneath to support both. The Starter Pack covers the core of that, or the Full Routine Bundle for the complete program.

There is also a preventative angle worth knowing. A dense, deep-rooted lawn is far less vulnerable to grub damage than a thin, shallow one, because it can lose some roots and keep going while it recovers. Building the lawn with the 5-step program is part of grub defence, not separate from it.

Frequently asked questions

When should I treat for lawn grubs in Australia?
September is the key window for grubs and beetle larvae, ahead of the peak egg hatch of African Black Beetle. For army worm and caterpillars the main pressure is late summer, with March a key control point. In both cases, treating preventatively before damage appears works far better than reacting after.

Do I need to see grubs before I treat?
No, and you are better off not waiting. By the time damage is visible the larvae are large, late-stage and much harder to control. A preventative application in September puts protection in the soil before the grubs can establish.

Is Acelepryn safe for children and pets?
Yes. Acelepryn is unscheduled and exempt from poison scheduling. It needs no protective equipment to apply, and the lawn is safe to use again as soon as the spray has dried.

How do I know if it is grubs and not something else?
Pull back a section of turf in a damaged patch and look at the soil beneath. White to cream C-shaped larvae 10 to 30mm long, and turf that lifts with no roots holding it, means grubs. Fast-spreading bare patches with heavy bird activity at dawn points to army worm. If water beads and runs off the surface instead, the problem is hydrophobic soil rather than pests, which is a different fix. If you are not sure, email a photo to info@turfandsurf.com.au and we will identify it.

Will Acelepryn fix the damage that is already there?
No. It stops the grubs causing further damage but cannot regrow turf that is already gone. Once the pest is controlled, rebuild the root zone and fill the patches back in with Vital, Surge and the soil program.