Armyworm

Armyworm in winter cereals

  • Common armyworm Leucania convecta
  • Northern armyworm Mythimna separata
  • Lawn armyworm Spodoptera mauritia

Download the table as a printable pdf.

Pre-emergence to flowering Grain development Ripening
Find insects and damagearmyworm
  • Prefer lush growth that provides good cover and protection
  • Feed on leaf tissue – leaf margins have tattered/chewed/scalloped appearance; in extreme cases whole leaves may be severed at the stem.
  • Caterpillars produce green/straw coloured droppings (size of match head). These are visible between the rows.
  • Bare patches adjacent to barley fields or damage to weeds may indicate armyworm presence before it is evident in crops.
In oats, pieces of panicles can be bitten off causing grain to fall to the ground Most damaging in barley close to harvest – larvae chew through stems below the head causing heads to drop.
Monitoring Monitor crops regularly (at least fortnightly at vegetative stage and increase frequency to weekly if larvae are detected and the crop nears maturity).

  • Use a sweep net, beat tray, beat sheet to check crops. Ground searches during the day are necessary to detect larvae sheltering under leaf litter and soil.
  • As larvae mature they will pupate in the ground under loose soil. Use a trowel to examine the soil between rows.
  • Note: armyworm are often unevenly distributed or confined to small portions of the crop
  • Traps, containing lures (10% port, 15% raw sugar and 75% water), can be used to indicate armyworm presence in the region
  • Check regularly for larvae and the first signs of head lopping.
  • Use sweep net, beat sheet and ground searches.
  • Increase the frequency of monitoring as the crop starts to dry down if above threshold populations of larvae are present.
  • Watch for level of defoliation of flag and flag-1 etc. which may impact grain fill.
  • In late spring, small larvae take 10-14 days to reach a size capable of head lopping. To determine if crop will be susceptible (dry, except for green nodes) when larvae reach a damaging size use the day degree estimates (beatsheet) for armyworm development.
Beneficials Around 20 species of predator and parasitoids have been recorded attacking armyworm. The most frequently observed predators are predatory shield bugs, ladybeetles, carabid beetles, lacewings and common brown earwigs. Parasitoids include tachnid flies and a number of wasp species (e.g. Netelia, Lissopimpla, Campoletis). Viral and fungal diseases are recorded as causing mortality of armyworm. Such outbreaks are more common at high armyworm densities.
Cultural control
  • Control weeds to remove alternative hosts. Armyworm often feed on ryegrass before moving into cereal crops.
  • Standing stubble from previous crops, dead leaves on crops and grassy weeds are suitable sites for female armyworm to lay eggs.

Larvae can move into cereals if adjacent pastures are chemically fallowed, spray topped or cultivated in spring. Monitor for at least a week post treatment. Damage is generally confined to crop margins.

Windrow or dessicate barley as an alternative to spraying for armyworm if rapid drying conditions are forecast.
Thresholds Barley

  • 2-3 large armyworm/m2 of crop (based on ground and plant sampling)
  • 1 head of barley/m2 equals 10 kg grain/ha (1 larvae/m2 can cause a loss of 70 kg/ha grain/day).

Wheat and oats

  • Economic threshold estimated at 10 grubs/m2 (higher than barley because heads are rarely lopped).
Pesticides
  • Effectiveness requires good coverage to get contact with the caterpillars. Control is more difficult in high-yielding crops with thick canopies where larvae are resting under leaf litter at the base of plants.
  • Armyworm are active at night – spray late afternoon or early evening to maximum likelihood of contact.
  • Be aware of withholding periods when chemical control is used close to harvest.
Multi-pest considerations
  • Control of armyworm in early crop development can have off-target impact on other cereal pests e.g. helicoverpa, aphids and mites.
  • Exposure to synthetic pyrethroids in these pests will contribute to selection pressure for SP resistance.
  • This is a consideration for insecticide use and selection, particularly in the northern region where H. armigera is prevalent and pests may move from winter crops to subsequent summer crops.
  • In the southern and western regions, SP use in winter cereals for armyworm may hasten or exacerbate SP resistance in earth mite species.
Communicate and discuss armyworm management Agronomists and growers can discuss:

  • Control of weeds and other green hosts especially ryegrass
  • Monitoring techniques and frequency , especially close to harvest
  • Control options and consider insecticide choices especially when other pests are present
  • Chemical choices and withholding periods
  • Good communication and sharing information with neighbours through area wide management may provide first indication of army worm presence
  • Industry publications provide up to date information about regional pest issues

Further information