Armyworms

Larvae are typically smooth, striped caterpillars ranging from green to brown or nearly black, reaching three to four centimetres at maturity, often with a pale stripe along each side. Adults are drab, night-flying moths rarely noticed except in large numbers after migratory flights.

The clearest field sign is rapid, extensive defoliation appearing over a short period, often with larvae found hiding under soil clods, in leaf litter, or at the base of plants during the day.

Moths often arrive on wind systems associated with rainfall and lay egg masses on leaves. Larvae pass through several instars, feeding mostly at night, with the final instars responsible for the bulk of defoliation before larvae drop to the soil to pupate. Several generations can occur in a season under favourable conditions.

Dense larval populations can strip leaves from plants within days, and where food is exhausted, larvae move en masse to adjacent, still-green vegetation, extending damage across a field or between fields. Seed heads and stems may also be attacked once foliage is depleted.

Host crops include maize, rice, and sorghum, along with pasture grasses and other cereals.

Pheromone traps for adult moths, combined with field scouting for egg masses and young larvae, especially after rainfall events associated with moth migration, support early detection before defoliation becomes severe.

Because armyworm populations can escalate quickly, management relies on early detection and rapid response within an integrated approach.

• Scout regularly, particularly after rain events linked to moth migration
• Conserve parasitoid wasps and flies, predatory bugs, and other natural enemies
• Use trenches or barriers to slow mass larval movement between fields where outbreaks occur
• Coordinate monitoring at a landscape scale, since outbreaks can affect neighbouring fields quickly