Armyworms

* Armyworms have started to appear in cereals but most damage occurs in barley, and at late crop ripening. * Look for evidence of armyworms well before the crop matures.

 

Where have they been reported?

Low to moderate densities (2-3 per m2) of armyworms have been found in a wheat crop (booting to stem elongation) east of Peak Hill, in the NSW Central West Slopes & Plains. The grubs were mostly foraging on the flag leaves.

Armyworm habits and behaviour

Armyworms are mostly pests of cereals and grasses. Moths typically lay eggs during winter and early spring. These hatch and the young grubs feed on plant leaves. Armyworm caterpillars mostly feed at night and hide during the day (except on very dull days) on the ground under leaf litter, or wedged in the crown of the plant.

They are normally most damaging towards the end of spring when crops, particularly barley, are close to harvest. This is because they chew through the last remaining green part of the plant stems, just below the head, causing the grain head to fall. Wheat can be damaged but typically only after very heavy defoliation (in extreme cases) or through an attack on secondary, thinner, tillers. Wheat stems are generally too thick to allow armyworms to chew through. 

There are 3 species of armyworms that typically attack cereals in winter and spring, although the common (Leucania convecta) and southern (Perectania ewingii) armyworms are most common.

Monitoring and control

Initial scouting for armyworm can be done by looking for signs of feeding damage to leaves (leaf scalloping). In the case of larger (>3 mm) grubs, look for their green to straw-coloured droppings (excreta), about the size of a match head, found on the ground between plants and cereal rows. Sweep netting the top of the crop in the early evening is useful to gauge the population size. Where warranted, treatment for armyworms should ideally be carried out in the late afternoon or early evening, as most species are nocturnal feeders.

Description

Armyworm caterpillars are most easily recognised by their three parallel white stripes running from the ‘collar’ behind the head, along the body to the tail end. The caterpillars are plump, smooth and hairless. They can grow to about 40mm long when fully mature. More information on armyworms is available on the IPM Guidelines for Grains website.

 

* Sources of field reports of armyworms

Glen Shepherd – Agronomist, IMAG Consulting (NSW Central West Slopes & Plains)