Armyworm (Spodoptera frugiperda, or Pseudaletia unipuncta), Lepidoptera

Armyworm biology & life cycle

Armyworms overwinter as larvae in soil. Next spring, larvae resume feeding until fully grown and then pupate in the soil. Adults emerge, mate and lay eggs in May and June. The next set of larvae emerge 1-3 weeks later and young larvae feed in groups at night. Feeding will continue for about 4 weeks until the larvae are fully grown. The second set of adults emerge in August. Typically, there are 2 generations per summer with the first generation doing to greatest damage in late June or early July.

Identifying Armyworm

Armyworm: eggs

Eggs are greenish-white in colour.

Armyworm: larvae

Young larvae are pale green and move like inchworms. Older larvae are greenish-brown with numberous white, orange and dark brown stripes which run the length of the larvae. The head is pale brown with a green tinge and mottled brown appearance. Both sets of larvae cause damage to dense cereal crops. Larvae feed on leaves, stripping the leaf margins and move up to feed on the panicles and flowers, stripping off awns and kernels. Lodged plants provide a favourable environment for all stages of the armyworm, The moths are concealed, lay eggs and larvae flourish in the high humidity underneath the dense crop.

Armyworm: Pupae

Pupae are reddish brown with fine black speckling.

Armyworm: adult

Adult moth is 25 mm long with a wingspan of 35-45 mm. Uniformly light brown in colour with a small, prominent white spot in the centre of each forewing.

Armyworm: management

Check fields in the evening or early morning when larvae are feeding on plants. Count number of larvae per square meter.