Management of armyworm in cereal crops

Page last updated: Tuesday, 19 January 2021 - 8:24am

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Armyworms are pests of cereal crops and historically have been frequently found along the south coast of Western Australia and occassionally in other wheatbelt localities. Armyworm are easily controlled by insecticides, especially if detected early and sprays are applied when economic damage is imminent. Barley crops can be extensively damaged by armyworm lopping barley heads in just a few days.

Recognising armyworm in crops

The first visible sign of armyworm caterpillars is often their green to straw-coloured droppings, about the size of a match head, found on the ground between the cereal rows.

Damage to weeds, especially their preference for ryegrass, is also a sign of their presence.

In barley crops

In barley crops, chewed leaves, heads and awns can be apparent, although the first sign is usually barley heads on the ground. As barley matures, part of the stem often remains green and appetising after other parts have dried. The caterpillars chew through this part causing the heads to fall to the ground.

In oat crops

In oat crops, the caterpillars bite off pieces of the panicle, causing grain to fall.

In wheat crops

Wheat crops are less frequently attacked and usually minor damage is caused as compared to damage in barley crops.

Barley heads fallen to the ground caused by armyworm caterpillars
Barley heads fallen to the ground caused by armyworm caterpillars chewing through the stems
Armyworm caterpillar damage showing chewing damage to barley
Armyworm caterpillar damage showing chewing damage to barley heads

Where to look for armyworm

Caterpillars of various sizes up to 4cm long may be seen in the crop. They may be on the plant or under leaf litter on the ground.

Description

The caterpillars hatch from batches of eggs laid in crevices, such as under the sheathing at the base of leaves. Caterpillars undergo a series of moults before reaching their full size of about 40mm long. They are fat and smooth and may be distinguished by the three parallel white stripes on the collar just behind the head.

Armyworm caterpillar. Note the three longitudinal white lines, especially on the collar,
Armyworm caterpillar. Note the three longitudinal white lines, especially on the collar, which help to distinguish it from other pest caterpillars of cereal crops.

When mature, the armyworm caterpillars burrow in soil to form pupae.

Adult moths emerge from the pupae.

Adults generally dull coloured moths with some species having metallic-looking markings on their wings.
Adults generally dull coloured moths with some species having metallic-looking markings on their wings

Four species of armyworm occur in barley growing areas. They are distinguishable in the moth stage; all are stout-bodied, light brown to grey moths with a length of about 30mm. Along the south coast, the most abundant species is the common armyworm (Leucania convecta).

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Author

Svetlana Micic