Insect pest problems
Armyworms
Armyworm is one of the biggest insect pest problems in Western Australian garden lawns. They can move quickly across a lawn and completely destroy it in the summer months. An average lawn can be eaten in two nights.
Adults are a dull brown or greyish, night-active moth up to 3.8cm long. Larvae (caterpillars) are up to 5cm long at maturity; they often curl up and lie still when disturbed. Armyworm larvae chew and cut leaves around the crown and they attack all turf grass species. Damage begins in small, irregular spots and spreads to patches extending some metres in width. Armyworms prefer moist areas. They are active from early spring through autumn. To control armyworms, reduce thatch and eliminate soggy areas. Larvae have some natural enemies, such as parasitic wasps and flies. If there are more than five larvae per square metre present, you may need to treat. An application of Bacillus thuringiensis (Bt) may be effective against young caterpillars. For chemical control, apply a registered lawn insecticide at night.
Cutworms
Cutworm adults are drab, heavy-bodied, night-flying moths. The fully grown caterpillars are fat and fleshy and about 35mm long. They curl up head-to-tail when disturbed. The caterpillars attack grass at ground level causing the blades to sever. They are nocturnal and shelter in the soil. For chemical control, apply registered lawn insecticide in the late afternoon.
African black beetle
The African black beetle is often falsely held responsible when dry patch is the real problem. The grubs of African black beetles feed from September to May and cut the grass from its roots. Lawn damaged this way can sometimes be rolled back like a carpet. African black beetle is considered a problem when 25 grubs per square metre are present. The adult beetles are less damaging. For more details refer to Lawn problems.
Couch mites
Couch mites are a common insect pest of home lawns. They are usually found within the forks of grass blades or shoots. Affected plants produce several shoots from the infested growing point.
Couch mites favour dry sites. To avoid spreading this pest, mow the affected areas last and clean the lawnmower afterwards. For chemical control, use a registered lawn insecticide.
Billbugs
Billbugs are an occasional pest on kikuyu grass from spring to autumn. Billbug larvae tunnel into the inside of turf grass stems and crowns.
As the larvae grow, they leave the stolons and feed below the thatch on rhizomes and roots. The affected area appears brown, thin, and dead in small, irregular spots. Affected grass can be easily plucked out by hand. For chemical control, apply a registered lawn insecticide.
Ants
Ants do not directly affect grasses. They build mounds and excavate underground tunnels, causing the turf to dry out and die. Ants are active in the warmer season in all grasses. Ants should be identified before control measures are untaken to ensure the correct insecticide is used. Refer to Coastal brown ants - big headed ants to gain a further understanding of ant behaviour and control. Ant samples can also be sent to the Pest and Disease Information Service (PaDIS) for identification and control recommendations. Ant samples should be sprayed first with fly spray and then stuck to clear sticky tape. Consult the Sending specimens for identification page for further advice.
Earthworms
Earthworms are more of a nuisance than a pest. Worm casts are thrown up on lawn surfaces, forming small mounds, particularly when soil is waterlogged after heavy rain. Earthworms are not damaging the lawn and are beneficial organisms with casts that provide fertiliser. They can be active all year on most grasses but if they are unwanted, aerate the soil with a garden fork.