There are either two to three generations each year in Missouri, but the larvae of the first generation in May and June causes the most feeding damage. Female moths prefer to lay their eggs in dense, grassy vegetation. In some years the true armyworm will only feed on plant foliage, whereas in other years it also may cut the awns and seedheads. True armyworms are most destructive to wheat and other small grain crops when wet weather causes lush growth and lodging in the fields. The true and fall are the primary armyworm pests on corn.
True armyworms begin feeding on the lower leaves before progressing to the top of the plant.
Damage appears as irregular notching at the leaf margins. Feeding damage is most common after a cold, wet spring that slows the plant s growth and reproduction of the true armyworm s natural enemies. Rank or dense fields of grasses or wheat are the common infestation sites for true armyworms. Scouting for true armyworms is best done at night or during early morning hours since armyworm larvae are mainly nocturnal feeders. They usually remain hidden on bright, sunny days.