Incidences of armyworm

Armyworms have been found in cereals from the Victorian Mallee and NSW Riverina – there’s no better time to brush up on your ID skills.

Armyworms are common caterpillar pests of broadacre crops in south-eastern Australia. Barley, oats and rice are most susceptible to economic damage, but they can cause also damage wheat, triticale and grass pastures. Damaging infestations in autumn and winter are almost always associated with crops sown into standing stubble, providing a medium upon which moths lay their eggs. There have been several confirmed instances of armyworms attacking cereal crops in the Victorian Mallee and parts of the NSW Riverina over the past 6-8 weeks.

During autumn and winter, armyworm caterpillars feed on the leaf margins, with larger larvae capable of completely defoliating plants. However, it is in late spring that barley crops are most susceptible to damage. The larger caterpillars, chew through the stem just below the head (the last green material left on the plant) causing heads to be lopped and fall to the ground. Wheat and triticale have thicker stems and are less susceptible to head loss.

Armyworm caterpillars are generally green, brown or yellow with three parallel white longitudinal stripes running from the ‘collar’ behind the head, along the body to the tail end. The body stripes can vary, but the collar stripes are always present. The caterpillars are about 1 mm long after hatching and grow up to 40 mm in length. There are three armyworm species commonly found in southern Australia: the common, southern and inland armyworms. They are difficult to distinguish apart, however, correct species identification in the field is generally not critical because their habits, type of damage and control are similar.

For information on distinguishing armyworm from other common caterpillars click here.

Armyworm on barley (left) and fallen barley heads as a result of caterpillar feeding (right) (Source: Copyright © Western Australian Agriculture Authority, 2015).

 

For more information on armyworm including their occurrence, lifecycle, behaviour and management strategies, visit armyworm within our PestNote series.

 

Field reports

Simon Craig – Agronomise Pty Ltd (Mallee, VIC)

Kris Dixon – Landmark (Mallee, VIC)

Luke Maher –  AGRIvision (Mallee, VIC)

Justin Whittakers – Landmark (Riverina, NSW)