How to apply lawn grub and armyworm treatments

A brown patch that spreads despite watering, turf that peels back like carpet, birds digging at the lawn every morning: these are classic signs of lawn grubs. Grass stripped to stubble in a few nights, with the damage spreading outwards, points to armyworm.

Both can be treated, but insecticides are among the more hazardous products a homeowner uses on a lawn. Many carry warnings about bees, fish and other aquatic life. So this guide starts with confirming you have a pest worth treating, then covers choosing a product, applying it so it actually reaches the pest, protecting everything else, and helping the lawn recover.

Confirm the pest first

Dry, water-repellent soil and uneven sprinklers cause brown patches that look very like grub damage. Spend a few minutes checking before you buy anything.

Curl grubs

“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.

1. 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.
2. Cut three sides of a spade-sized square and fold the turf back like a flap. If grubs have been feeding, it may lift with almost no resistance.
3. Look in the root zone and the top few centimetres of soil for C-shaped, cream grubs with brown heads and three pairs of legs near the head.
4. Check two or three patches and one healthy-looking area to see how widespread they are.

Armyworm

Lawn armyworm are caterpillars, not grubs. They feed on leaves, mostly late in the day and at night.

1. Look for grazed patches that look as if they’ve been mown very short, with ragged, chewed leaf edges, spreading quickly over days.
2. Check at dusk or after dark with a torch. Part the grass at the edge of a damaged area and look for striped caterpillars and their droppings.
3. Watch for moths around outside lights in the evening.

Neither?

If you find no grubs or caterpillars, the patch may be dry soil. Do the water drop test: pour a little water on the patch and see whether it soaks in or beads on the surface. Check your sprinkler coverage with a catch-cup test too. An insecticide won’t fix either problem.

Is it worth treating?

Finding one or two grubs doesn’t always mean you need to treat. A healthy lawn can cope with some, and many will be eaten by birds. Treat when you find enough to explain the damage and the damage is spreading.

For armyworm, the Queensland Government’s guidance for lawns is to act when you see rapidly expanding areas with more than 60% leaf loss. Small, stable areas of damage often recover with water and fertiliser, because armyworm eat leaves rather than roots.

Grubs or armyworm: why it matters

The product has to reach the pest. A product for grubs needs to get into the root zone; a product for armyworm needs to be on the leaves where they feed. That’s why the label’s directions on timing and watering in matter so much.

Choosing a product

The label must list:

• the pest you’ve found, such as curl grubs, African black beetle or lawn armyworm;
• the situation, such as home lawns or turf; and
• any directions or restrictions relating to your grass type.

If a product’s label doesn’t list your pest, it isn’t registered for that use, and using it that way can be illegal. You can check a product’s registration and read its label on the APVMA’s PubCRIS database.

Lawn insecticides come as granules, spread with a spreader, and liquids, applied with a hose-end or pump sprayer. Some are registered for use before damage appears, and others for treating an infestation you’ve found. The label tells you which, and when to apply.

When to apply

• When the pest is active and feeding. The industry identification guide we use places African black beetle larvae in lawns from early spring to mid summer, although timing varies with the season and the species. Armyworm are most common in the warm months.
• At the time of day the label gives. For armyworm, which feed late in the day and at night, products are usually applied late in the afternoon, where the label allows.
• On a calm day, with no rain forecast within the label’s rain-free period, and no heavy rain that could wash product off the lawn and into drains.
• Not when the lawn is stressed by heat or drought, unless the label says otherwise. Water a dry lawn a day or two beforehand if the label suggests applying to moist soil.

Protect bees and waterways

Insecticides can harm bees. BeeAware, Plant Health Australia’s bee program, explains that bees can be poisoned when a chemical lands on flowering weeds under the target, or drifts onto bees, flowering plants or their water. Before you apply:

• Mow the lawn to remove flowers from clover, bindii and other flowering weeds, so bees aren’t foraging there.
• Keep spray and granules off flowering garden plants.
• Follow every bee warning on the label.

Many lawn insecticides also carry warnings about fish and other aquatic life. Keep them out of drains, ponds, creeks and water features. Don’t apply them to paths and driveways, and sweep up any granules that land there.

Before you start

• Read the whole label: rate, timing, watering in, protective equipment, re-entry directions, bee and aquatic warnings, and disposal.
• Measure the area you’ll treat with the Lawn Area Calculator, and work out how much product you need with the Product Application Calculator.
• Calibrate your equipment. See the broadcast spreader guide or the sprayer calibration guide.
• Put on the protective equipment the label lists before you open the pack.
• Bring in children, pets, toys, bowls and washing. Cover fish ponds if the label warns about aquatic life.

Applying granules

1. Fill the spreader on a tarp or hard surface, never on the lawn.
2. Do the edges first, using an edge guard so granules stay off garden beds and paths.
3. Walk even, overlapping passes at a steady pace, closing the gate when you stop or turn.
4. Sweep any granules off hard surfaces back onto the lawn.
5. Water in as the label directs. Curl grubs feed below the surface, so the label’s watering directions are what move the product down to them. Water until it soaks in, not until it runs off.

Applying liquids

1. Mix exactly as the label directs, outdoors and away from drains, measuring with equipment kept only for chemicals.
2. Apply evenly with a calibrated pump sprayer or a hose-end sprayer, in parallel strips with a slight overlap.
3. Keep the nozzle low and the pressure moderate, so the spray doesn’t drift.
4. Water in, or don’t, exactly as the label says. A product meant to stay on the leaves for armyworm may be less effective if watered in too soon, while one meant for grubs may need watering in.

Whole lawn or just the patches?

Follow the label. Many people find grubs or armyworm confined to part of the lawn. Where the label allows, treating the affected area and a margin of healthy-looking lawn around it uses less product than treating everything. Check a few spots across the whole lawn before you decide, because damage often shows up in one place before another.

After applying

• Keep people and pets off the treated area for as long as the label says.
• Wash your gloves before taking them off, then wash your hands and any clothes that got product on them.
• Clean equipment as the label directs, and never rinse it into a drain.
• Store the product in its original container, locked away from children and pets.

If anyone swallows the product or gets it in their eyes, follow the first aid directions on the label and phone the Poisons Information Centre on 13 11 26. For pets, contact your vet or the Animal Poisons Helpline on 1300 869 738.

Has it worked?

After the time the label gives for the product to work, check again:

• For grubs, lift a piece of turf at the edge of the damaged area. Fewer or no live grubs means the treatment worked.
• For armyworm, check at dusk with a torch. The edge of the damage should stop advancing.

Don’t re-treat just because the lawn is still brown. The grass takes much longer to recover than the pest takes to die. Re-treat only if live pests are still active and the label allows another application.

Helping the lawn recover

• Water deeply within your local water rules, so new roots and leaves can grow.
• Feed lightly at the label rate once the lawn is growing again. Queensland’s guidance notes that lawns damaged by armyworm can recover with fertiliser and water.
• Keep traffic off damaged areas while they regrow.
• Repair dead patches once the lawn is growing strongly. Grasses that spread by runners, such as buffalo, couch, kikuyu and zoysia, often fill small patches themselves; larger ones may need topdressing or new turf.

Reducing the risk next season

• Keep the lawn healthy. A lawn that isn’t stressed by dry or compacted soil copes better with some pests.
• Check during the risky months. Lift a piece of turf in late spring and look at the lawn at dusk in summer.
• Watch the birds. A sudden increase in birds digging at the lawn is often the first sign of grubs.
• Note where damage started this year. Pests often return to the same areas.

Common mistakes

• Treating every brown patch without lifting the turf to check.
• Using a product whose label doesn’t list the pest.
• Applying grub products without watering in when the label says to, so the product never reaches the root zone.
• Applying over flowering weeds while bees are foraging.
• Letting granules or spray reach drains and waterways.
• Re-treating too soon because the grass is still brown.

Log it

Log the pest you found, where and how many, the product, the area treated and the date. Add a note when you check the results. Next year, your journal will tell you when and where to start looking.