They are usually unnoticed until they are 25.5 to 38.5 mm long, by which time, if abundant, they have consumed so much foliage that they create alarm. Unlike the nocturnal true armyworms, fall armyworms feed any time of the day or night, but are most active early in the morning or late in the evening. When abundant, these caterpillars may eat all the available food and then crawl in great armies to adjoining fields. After feeding for 2 or 3 weeks, the larvae dig about 20 mm into the ground to pupate. Within 2 weeks, a new swarm of moths emerges, usually flying several miles before laying eggs.
Several generations occur each in North Carolina.
Cold, wet springs seem to reduce the effectiveness of these parasites and a population explosion often results. Early planting is the most effective cultural control method in the South. When 80 percent of the plants in a field of corn or sorghum have at least one fall armyworm feeding in the whorl, control is justified. If there are two or more caterpillars per plant, controls should be initiated when 40 percent of the corn plants or 50 percent of the sorghum plants are infested. For further control information, consult the current North Carolina Agricultural Chemicals Manual .