Common armyworm in winter cereals

The common armyworm (Leucania convecta ) is important in southern Queensland where it attackes winter cereals, particularly barley and oats, in September and October. Larvae appear in plague proportions in some years, and are patchy in others. Conditions leading to outbreaks are not yet fully understood. Leafy cereal plants can tolerate considerable feeding from moderate numbers of armyworms. Control in the vegetative stage is seldom warranted unless large numbers of armyworms are well distributed throughout the crop and are destroying young seedlings or the younger two or three leaves from older plants.

Infestations within padocks are often patchy and more luxuriant stands often have the highest pest pressure - up to 60 or more armyworms per square metre. Larvae hide in leaf debris or in cracks in the soil and emerge at night to feed. Infestations are indicated by the eaten-out margins of leaves and also by the faecal pellets around the plant base. Older larvae can feed on the green stem just below maturing heads, severing them.

The most serious armyworm damage in cereal crops occurs when it starts feeding on the upper flag leaf and stem node as the crop matures. Head cutting begins at this time. Control is warranted if the armyworm population distributed throughout the crop has potential to cause the loss of 15 heads per square metre. Populations in excess of 1 larva per square metre will usually warrant spraying. For insecticide application to be economic, check or scout the crop and assess the problem before head cutting starts. Check for larvae on the plant and in the soil litter under the plant. Only large larvae can chew through the stem.

Armyworm can be parasitised by a small wasp (Apanteles spp) - wasp larvae can be seen developing within the catepillar if it is broken open, or pupating wasps are visible as cocoons attached to the caterpillar's body.

Last Updated March 2004