Fall Armyworm
Spodoptera frugiperda (J.E. Smith), Noctuidae, LEPIDOPTERA


DESCRIPTION

Adult -The moth has a wingspan of about 38.5 mm. The hind wings are grayish-white; the front wings are dark gray, mottled with lighter and darker splotches. Each forewing has a noticeable whitish spot near the extreme tip.

Egg - Minute, light gray eggs are laid in clusters and covered with grayish, fuzzy scales from the body of the female moth. The eggs become very dark just before hatching.

Larva - About 30 to 40 mm long, the full-grown larva varies in color from light tan or green to nearly black. Along each side of its body is a longitudinal, pitch-colored stripe, and down the back is a wider yellowish-gray stripe. Unlike the true armyworm, the head of the fall armyworm is often marked with a pale, but distinct, inverted "Y." Color plate.

Pupa - The pupa, approximately 13 mm long, is originally reddish-brown and darkens to black as it matures.


BIOLOGY

Distribution -The fall armyworm is a continuous resident of the Gulf states, the tropics of North, Central and South America and some of the West Indies. Each year it migrates as far northward as Montana, Michigan and New Hampshire. In the southeastern states, it occurs annually on late corn and reaches epidemic populations in sorghum about once in 3 years. Fall armyworms annually attack late corn and sorghum in the North Carolina Coastal Plain and Piedmont.

Host Plants - Corn, sorghum, and other plants of the grass family are the preferred foods, but the fall armyworm also attacks alfalfa, bean, peanut, potato, sweet potato, turnip, spinach, tomato, cabbage, cucumber, cotton, tobacco, all grain crops, and clover.

Damage - In North Carolina, the fall armyworm can be a serious pest of corn in July and August. Light populations occur annually; however, heavy populations (one or more larvae per plant) occasionally occur and can be very difficult to control.

The most frequent damage by the fall armyworm is to the whorl of late pretassel corn or sorghum. Several larvae may feed throughout the tightly coiled blades. This feeding results in numerous ragged holes when the blades unfurl and may prevent infested plants from producing normal ears or seed heads. As with the corn earworm, wet, tan excrement can be found lodged in the remaining blades and blade axils.

In addition to defoliation, damage to corn may occur in three other ways. First, larvae feed on the undeveloped tassels of young plants. Secondly, immature ears are attacked. Last of all, large larvae may bore into stalks.

Life History - This insect overwinters in Florida and along the Gulf Coast in several life stages, but usually as pupae. Egg- laying moths usually appear in North Carolina about the middle of July. Each female lays about 1,000 eggs in masses of 50 to several hundred. Two to ten days later, the small larvae emerge, feed gregariously on the remains of the egg mass, and then scatter in search of food. 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.


CONTROL

During favorable seasons, a number of parasitic enemies keep fall armyworm larvae down to moderate numbers. 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.