Lepidoptera

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Lawn Armyworm is an introduced species and is a major pest of gardens. Caterpillars - the damage-causing stage of the Lawn Armyworm lifecycle - predominantly feed on tender new growth of leaves and seedlings.

Best Treatment for Lawn Armyworm

To prevent a major infestation and severe devastation to lawns, turfed areas and garden plants, it is best to kill and control caterpillars at the earliest sign of infestation.

For the control of Lawn Armyworm at the caterpillar stage on lawns and turfed areas, try:

  • Yates Baythroid Advanced Insect Killer for Lawns
  • Yates Insect Killer for Lawns

For the control of caterpillars, including armyworm, on plants (please check label registration and instructions for product suitability), try:

 Physical control

Please note, while these techniques may help to reduce a caterpillar population, complete control is unlikely to be achieved using physical control methods alone. For optimal control, further treatment is required. A combination of monitoring, preventative strategies, sprays, physical controls and cultural controls makes an ideal integrated pest management program.

  • At night, place moistened hessian bags, damp towels or pieces of carpet near damaged vegetation for caterpillars to hide underneath. In the morning, collect caterpillars hiding underneath and either feed to the birds or place pests into a bucket of soapy water. Drain off the excess water, place dead pests in a plastic bag and place into the rubbish bin.
  • At night, use a lawn roller on lawn and turfed areas to squash and kill caterpillars.

Reviving a damaged lawn or turfed area

  • Rake up dead and decomposing turf. Collect material, either by hand or use a lawn mower with catcher attached, then place material into the green bin.
  • Keep the area well-watered and fertilised to promote fast healthy growth. Try one of our Yates lawn fertilisers.

For particularly vast areas of bare lawn/turf, or where the lawn/turf has died, repair with lawn seed. Try one of our Yates lawn seeds.

What are Lawn Armyworms and How to Get Rid of them

Armyworms are generally found in the Northern Territory, Queensland, New South Wales and the Australian Capital Territory.

It’s called ‘Armyworm’ because of the army-like nature, where large numbers march into an area and feed on lawns, turf and various plants in the garden, swiftly decimating expansive areas of vegetation.

Lawn Armyworm can develop rapidly into near plague proportions and quickly cause significant damage in the garden. To help control these destructive pests, it’s important to regularly monitor, identify correctly and treat at the earliest sign of infestation.

Description, Lifecycle, Habitat and Behaviour

During its lifetime, Lawn Armyworm undergo complete physical transformation (also known as holometabolous metamorphosis). Eggs hatch into larvae (caterpillars), larvae grow and develop through various stages, larvae pupate, then finally emerge as adult moths. The lifecycle generally lasts for five to nine weeks, with two to four generations per year in spring and summer.  In ideal conditions, activity may extend into autumn. Severe infestations can occur after a period of dry conditions followed by wet.

Eggs

After mating, the adult female moth lays eggs in a cluster of 150 - 200, covering them in a mass of grey-hairs (setae). Eggs are generally laid in dense vegetation at the tip of a leaf but may also be found on hard surfaces and structures near a food source. Females generally lay 1800 - 2000 eggs over a period of five to six days, later dying after reproducing. Eggs are round-to-oval shaped and 0.5 mm in diameter. Eggs are initially a creamish-tan colour, darkening with age. After incubating for two to five days, eggs hatch into larvae (caterpillars).

Larvae

The caterpillar larvae are the damaging stage of the Lawn Armyworm lifecycle. Larvae develop through five to six stages (instars) where caterpillars grow then shed their exoskeleton - a process known as moulting.

The body is smooth, soft, tubular and heavily segmented. At the front of the body is a rounded head capsule with a distinct inverted ‘Y’ marking on the forehead. On the underside of the head are chewing mouthparts and inconspicuous antennae. Attached to the underside and front section of the body (thorax) are three pairs of short and pointy legs - these are the ‘true legs’. Further along the body are four pairs of abdominal ‘pro legs’ and at the last body segment is one pair of ‘anal prolegs’.

The first instar is 1 mm long, the body is white with a black head capsule. Instars gradually develop into a green colour with yellowish-white stripes extending longitudinally from the neck to the tip of the abdomen.

The final instar is up to 40 mm long with a greyish-brown body and dark brown head capsule. On the upper and lower sides of the body are green, grey and beige longitudinal stripes. On the upper side of the body, along either side of the back, are two distinct rows of paired, black, semi-circle markings, occurring at each segment.

When disturbed, caterpillars drop to the ground, tuck their head into their abdomen and form into a spiral-like shape.

Caterpillars can spin silk which is produced from salivary glands in the mouth. Silk is used for attachment to plants; travelling to new areas of vegetation by silken threads being caught by the wind; and spinning cocoons for pupating.

Mostly seen in the evening and at night - especially mature instars – they hide during the day underneath clods of soil, beneath vegetation or in lawn thatch. However, on overcast days or when in large numbers, they may also be seen during the day.

Pupae

After 17-32 days, mature larvae burrow into the soil and dig a chamber to create an ‘earthen cell’. The larva forms a cocoon made from soil, vegetation and webbing.  As pupae mature they become glossy, smooth, hard, a dark reddish-brown and approximately 16mm long.

Adults

After pupating for seven to ten days, adult moths emerge, mate one to two days later and survive for one to two weeks.

The body is dull light-brown, long, stout and approximately 20 mm long. The abdomen is segmented and narrower towards the end.

The head and body are covered in hair-like scales (setae). On either side of the head are a pair of large, rounded, blackish-brown compound eyes. Above the eyes are a pair of long, thin and light-brown antennae - primarily used for sensing smell. On the underside of the head is a long and thin feeding tube (proboscis) which remains in the curled position at rest and extends when feeding on the nectar of flowers.

Attached to the underside and front section of the body (thorax) are three pairs of long and slender legs. Legs are mostly dark brown with white joints. The upper leg of the male foreleg is densely covered in tufts of light-brown hair-like scales.

Attached to the upper-side of the thorax are two pairs of membranous scaly wings with a wingspan up to 40 mm wide. Forewings are mostly brown with a light brown, beige and dark brown mottled pattern. Hind wings are shiny, plain and off-white with dark veins. At rest, wings fold down along the length of the body, forming an inverted ‘V’ shape. Adult moths can fly and travel long distances, usually in September and October.

Natural enemies

Birds, frogs, spiders (including the Bird-Dropping Spider), wasps, lacewings, ladybugs, nematodes, viruses and other diseases. 

Symptoms of Lawn Armyworm damage

Dead or dying patches in lawn and turfed areas:

  • May be light-brown or have a straw-like appearance.
  • Mostly seen in spring and summer due to peak activity of caterpillars - in ideal conditions, activity may extend into autumn.
  • Appears very quickly and spreads rapidly over a period of nights.
  • Often starts as a small patch, with damage radiating outwards over time.
  • May begin along the outer edges near garden beds or in areas where turf is dense and long.

Damage to turf and plant leaves:

  • Skeletonised leaves.
  • Chewed and tattered leaf tips and leaf margins.
  • Complete defoliation of plant often associated with remnant leaf midribs.

Further evidence of Lawn Armyworm are the presence of eggs, larvae, pupae, adults, webbing and faeces/droppings (green-yellow pellets)

How to Prevent Lawn Armyworm Appearing

Monitor

  • As Lawn Armyworm populations develop so rapidly, it is important to be vigilant for any signs or symptoms of pests in the garden (see ‘Symptoms of Lawn Armyworm Damage’).

To determine the presence of caterpillars:

  • At night, shine a bright torch onto turfed areas or plants suspected of attack, look closely for signs of webbing or caterpillars.
  • In the evening, fill a 9L bucket with water and mix in some dishwashing detergent. Slowly pour the contents of the bucket onto a 1 metre square area of partially affected lawn or turf suspected to be infested with pests. Place a damp towel, hessian bag or piece of carpet on top, wait 15 minutes, then inspect for caterpillars. If no caterpillars are observed, leave overnight then re-examine in the morning.

To determine the presence of adult moths:

  • At night, turn on bright outdoor lighting and wait for moths to congregate around light source.

 Cultural control

  • To prevent subsequent year damage, ensure current season pests have been adequately controlled.
  • Regularly mow lawns and turfed areas short, to reduce egg laying site suitability and overabundance of caterpillars’ food source.
  • Regularly dethatch lawns and turfed areas to reduce day-time hiding places for caterpillars.

Avoid using bright outdoor lighting at night as this may attract flying adult moths into the garden.

What plants are impacted by Lawn Armyworm 

Lawns and turf are most significantly impacted, with any turf variety subject to attack, such as:

  • Buffalo
  • Couch
  • Kikuyu
  • Ryegrass
  • Fescue
  • Bermuda
  • Clover

 While Lawn Armyworm is best known for damaging lawns and turf, crops and non-edible (ornamental) plants are also affected, such as:

  • Asparagus
  • Barley
  • Brassicas (e.g. broccoli, cauliflower, kale, etc.)
  • Nutgrass
  • Oat
  • Papaya/Paw Paw
  • Rice
  • Sorghum
  • Wheat

 Non-edible (ornamental) plants, such as:

  • Grasses, sedges and strappy-leafed plants
  • Bamboo
  • Canna Lilies
  • Clover
  • Horsetail She Oak (Casuarina equisetifolia)
  • Palms
  • and many more.

Recommended Products to control Lawn Armyworms


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