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Fall Armyworm (Spodoptera frugiperda)
Description and Biology: Young larvae are greenish and have black heads. Mature larvae vary from greenish to grayish brown and have a light-colored, inverted, Y-shaped suture on the front of the head, and dorsal lines lengthwise on the body. The moth has variegated gray front wings. Eggs in masses covered with scales and hair of the moth usually are deposited on the underside of leaves or in panicles. The insect requires about a month to complete a generation. No life stages are known to diapause or aestivate. Adults migrate northward from subtropical and tropical America each year as the temperature warms.
Symptoms and Damage: As do corn earworms, fall armyworms
infest both the whorl and panicle of sorghum. Before sorghum panicles
are present, fall armyworms sometimes infest the whorl where larvae feed
on tender leaf tissues. When leaves unfurl, irregular, elongated feeding
areas or a row of holes across the leaves are visible. Although rare,
larvae may feed on panicles not yet emerged from the whorl. To locate
fall armyworms in sorghum whorls, the whorl leaf must be pulled from the
plant and unfolded. Frass is present where the larvae feed within the
Monitoring: Just as for corn earworms infesting the whorl and panicle of sorghum plants, different methods of sampling are required. Sampling techniques for fall armyworm are the same as those provided previously for corn earworm.
Management: Several wasps and flies parasitize fall
armyworm, several bugs and beetles prey on this pest, and pathogens, especially
fungi, infect and kill fall armyworm larvae. Early planting before fall
armyworm moths migrate into temperate zones is an important management
tactic to escape infestation. Insecticidal control of fall armyworm larvae
in sorghum whorls usually is not feasible. Chemical control may be justified
if larval feeding is damaging more than 30% of leaf tissue or the developing
panicle, but this situation seldom occurs. Early planting of sorghum hybrids
with loose (open) panicles is an important management practice. Insecticidal
control usually is justified when there is an average of two larvae per
panicle less than 25 mm long or one larva longer than 25 mm.