Lawn Armyworm in Australia: Identification, Damage, Prevention and Treatment Guide.

Lawn armyworm (Spodoptera mauritia) is the most destructive warm-season turf pest in Australia, capable of stripping couch, kikuyu and ryegrass overnight.

The first signs of damage are scalloped turf edges, thinning cover, and small areas of window-paning. Large larvae can eat whole leaves and leave patches that brown off within hours.

These outbreaks are common in the late summer and the early autumn across Australia, especially on irrigated couch, kikuyu, and ryegrass surfaces.

Lawn Armyworm Identification.

The key to identification is colour, stripes, head shape, lifecycle and behaviour.

• Early larvae are small.
• They are pale and have fine stripes.
• Mid larvae are dark with more obvious bands.
• Mature larvae are much thicker, patterned caterpillars.
• They are 20 to 30 mm long, and when you disturb them, they curl into a tight “C” shape.
• They feed mainly at dusk and in the evening. This means you are best to check for activity at night or carry out a simple soapy-water flush.
• Damage tends to appear first on edges, goal mouths, field banks, and irrigated hot spots.

Lawn Grub vs Lawn Armyworm.

• In Australia “Lawn grubs” are root-feeding beetle larvae. These are also known as curl grubs or scarab beetle larvae.

• In contrast armyworms are leaf-feeding caterpillars that strip the foliage above the ground.

Both of these pests cause similar damage to turf, but where the damage occurs tells you which pest you have.

Lawn Grubs.

The lifecycle of the lawn grub is eggs to Larvae (curl grubs) to Pupae and then they become an adult beetle.

Where they feed:

• Below the surface. They chew roots and stolons, and seldom shred leaves.

Key signs:

• Turf lifts easily like a loose carpet.

• Grass dies from the roots upward.

• Birds dig at the turf to pull the larvae out.

• Damage develops much more slowly compared to armyworm.

Appearance:

• Lawn grubs are a White, C-shaped grub with a brown head and have six legs near the front of their body.

What Armyworms Are

The armyworm lifecycle comprises eggs to Larvae (these are the caterpillars) to Pupae and they then become a Moth.

Where they feed:

• These feed above the ground. They chew leaves and stems.

Key signs:

• Damage tends to be seen as the leaves have scalloped edges or are shreddedand you can see window-pane damage.

• Turf tends to rapidly brown off. This sometimes happens overnight.

• You see larvae on the surface, especially at dusk.

• The moths fly around lights. You find egg masses on walls and fences.

Appearance:

• A smooth caterpillar with yellow/white/dark stripes.

• Larger larvae curl into a tight “C” if you handle them.

Damage Speed

Which Pest Do You Have?

Lawn Armyworm Geography.

Armyworm outbreaks are common in the warm and humid regions of Australia. You see them most often across coastal and sub-coastal QLD, northern and central NSW, the ACT, and parts of VIC in the late summer and the early autumn.

Field observations show a repeat pattern of peak feeding pressure after hot spells and irrigation. This pattern has been seen consistently across NSW and QLD on couch, kikuyu, and ryegrass sports surfaces.

Why Lawn Armyworm Cycles Boom in El Niño and La Niña Years.

Armyworm populations rise sharply during both El Niño and La Niña, but this is for different reasons. In Australia, these climate phases shift temperature, humidity, and rainfall patterns, and directly accelerate the insect’s lifecycle and survival.

In An El Niño Heat Drives Outbreaks.

In an El Niño the temperature increases, rainfall falls, there are more frequent heatwaves and there is an increase in turf irrigation. These conditions cause armyworm outbreaks because higher temperatures accelerate development.

In an El Niño summer there is a rapid GDD accumulation. This causes:

• Eggs to hatch faster.
• Larvae to grow quicker and reach a damaging size earlier.
• There to be more generations over a season. El Niño summers often have 2 to 3 overlapping generations, in contrast to the usual 1 to 2.

Drier weather increases moth activity.

Moths fly further and more consistently in dry, warm air. This increases:

• Egg-laying across larger areas.
• The number of egg masses on walls, fences, and light structures.

Irrigation creates “green islands”.

When rainfall falls, irrigated turf becomes the best food source in the area. Armyworms tend to target:

• Ovals.
• Golf fairways.
• Parks.
• Sportsgrounds.

These irrigated areas sustain fresh leaf tissue, and draw in adults from the surrounding dry environments.

La Niña Years. Moisture-Driven Outbreaks.

La Niña causes higher humidity, above-average rainfall and increased cloud cover and warm nights. This produces a different set of conditions that favours armyworms.

High humidity Increases egg and young larvae survival.

Egg masses desiccate easily in dry weather. In a La Niña:

• Moisture protects the egg masses.
• Young larvae avoid early-stage mortality.
• More larvae reach large, damaging stages.

Warm nights accelerate feeding.

Armyworms feed intensively at night. At night during a La Niña:

• Conditions stay warm for longer.
• There is an increase in the hours of continuous feeding.
• This causes an increase in the rate of leaf loss and more severe outbreaks.

Heavy rain causes flushes of new turf growth.

New growth means an increase in food for armyworms.

Sports turf often:

• Recovers rapidly.

• Then gets hit again.

• This leads to multiple “waves” of damage within a single La Niña season.

More vegetation means there are more egg laying sites.

Rapid plant growth around turf facilities (banks, fence lines, unmaintained surrounds) increases egg-laying surfaces.

Why Both Climate Patterns Increase Risk.

In short:

• El Niño ≈ faster cycles.

• La Niña ≈ higher survival + heavier feeding.

Both lead to boom years, but due to different biological mechanisms.

Field Observations from NSW & QLD Turf Sites (2018–2024).

Across couch, kikuyu, and ryegrass surfaces:

• In El Niño seasons after heatwaves there tend to be high-intensity bursts of armyworm feeding.

• La Niña seasons produce persistent, long-running infestations, with repeat peaks after rain events.

• Irrigated sports turf always acts as a magnet for adult moths under both patterns.

• Multi-generational overlaps are common in both conditions. However the causes differ (heat vs survival).

How Climate Phases Influence the GDD Model.

El Niño.

GDD accumulates rapidly so that predicted larval peaks arrive earlier.

La Niña.

GDD accumulates normally, but:

• Egg survival rates rise.

• Feeding hours extend.

• Larval populations grow outside normal heat thresholds.

This produces unexpected late-season spikes, especially in humid autumn periods.

How To Predict Lawn Armyworm in Australia.

Temperature controls the development rate of the Armyworm, which makes it ideal for heat-based modelling.

• A growing degree day (GDD) model measures how much heat the insect receives once the eggs are laid.
• Each life stage needs a set amount of heat to develop. In Australia, Lawn Armyworm completes a single generation in about 500 GDD above a 12 °C base.
• This GDD threshold (522 GDD base 10°C) is based on Australian field observations taken from NSW and QLD sports fields between 2018 to 2024.
• If you track the heat from a “biofix point”, you can estimate egg hatch and early larvae stages.
• By doing this it also shows when large late stage larvae will begin to cause damage. This gives a clear warning window in comparison to visual scouting.

This model removes guesswork, reduces waste, and helps you match the right product to the correct growth stage. Our Lawn Armyworm Predictor uses local temperature data, and gives you a practical forecast.

Biofix Date.

A biofix date is when you first see a clear events such as egg masses, early larvae, or an increase in moth flights. Once you set the biofix date, the model uses BOM max and min temperatures to calculate the daily GDD totals and predict the life stage.

Lawn armyworm egg masses on a wall.

How to Monitor For Lawn Armyworm.

• If you regularly monitor it prevents you having any nasty surprises.
• Check the turf edges and lights for moth flights.
• Search for egg masses on posts, fences, and nearby plants.
• Use a soapy-water drench to flush any larvae out of the thatch.
• Watch for thinning turf areas, ragged leaf tips, and rapid browning.

If you combine field checks with this model it gives a much clearer picture of any risk. This then allows you to carry out any treatment before large areas of turf are lost.

Prevention.

Prevention helps limit damage.

• Maintain adequate turf nutrition to help with strong recovery.
• Reduce thatch levels where possible.
• Keep your height of cut consistent.
• If any damage occurs, irrigate and apply light rates of N to help with recovery.
• Where turf density drops, refer to our integrated lawn weed management guide to prevent opportunistic weed invasion.
• Maintaining adequate soil moisture uniformity helps limit stress. Tools like the Soil Wetting Agent Selector assist with consistent infiltration.
• These steps support plant health and help the turf rebound after damage.

Lawn Armyworm Treatments and Growth Stage.

You need to use different products to control early larvae than for large larvae or pupae. If you match your chemical use to the growth stage it increases your success and reduces waste.

Timing.

• The best time to treat this pest is when they are young larvae. These respond the best to diamide insecticides.
• These will continue to work on mid larvae but at this stage you can also use indoxacarb.
• Once they become larger you will start too see damage and at this stage you need to use a pyrethroid for a quick knockdown.

Control involves good timing and the use of the right products. Early intervention is always more effective.

Insecticide Resistance Management.

• Group 28 (diamide) insecticides give long residual protection and are ideal for early to mid larvae.
• You can use Group 22A (indoxacarb) in the mid stages.
• Group 3A (pyrethroid) insecticides give a rapid knockdown when large larvae are present.

If you use the right selective, rotate MOA groups, and make sure that you follow the label it reduces the resistance pressure and improves your long-term control.

This GDD model does not replace physical checks, but it gives a clear warning window well before any damage will appear in the turf.

This is especially useful on sports fields and top tier lawns that rely on uniform cover and cannot afford any sudden loss of grass.

The ‘KISS’ System For Lawn Armyworm.

• The approach is simple. Warm days mean faster development. Cool days mean slow development.
• If you look at the amount of accumulated heat rather than the calendar date, you get a much clearer picture of the risk.
• Daily temperature inputs for Lawn Armyworm modelling can be drawn directly from the Bureau of Meteorology. The model uses BOM maximum and minimum temperatures to calculate degree-days above the 12 °C base.
• This gives a more accurate, site-specific estimate than seasonal averages.
• Most sports turf managers already use BOM data for irrigation planning or heat-stress risk.

As a company Gilba Solutions fully supports the development of predictive models and in 2025 we have launched several such as the Argentine Stem Weevil Predictive Model and the Soil Compaction Model to help turf professionals and lawn owners.

For Lawn Armyworm, the goal is early detection and early action. This model gives turf managers a practical way to stay ahead of an insect that can cause severe damage in a short period of time.

Common Mistakes People Make With Lawn Armyworm.

• Spraying late-stage larvae too late.
• Mowing too low after damage.
• Relying on pyrethroids too early.
• Not checking for egg masses after treatment.
• Watering immediately before spraying.
• Assuming that any brown patches are the result of armyworm. More often than not they are the result of drought or a hydrophobic soil.

References.

Queensland Department of Agriculture and Fisheries (DAF): Armyworm and pasture pest updates.
IRAC (Insecticide Resistance Action Committee): Mode of Action Classification Scheme.
Australian Turfgrass Management Journal: seasonal pest behaviour reports.
Bureau of Meteorology (BOM): Climate Data Services for Tmax/Tmin records.