Fall Armyworm, Spodoptera frugiperda, Lepidoptera: Noctuidae

Description

Fall armyworm adults are large bodied moths with dark gray forewings that have lighter banding. A light spot occurs near the apex of the forewings. Mature larvae are up to 1.5 inch long and are dark brown in color with numerous black spots (Photo 9). The head capsule has a distinct light colored inverted “Y”.

Distribution, damage and impact

Fall armyworm occurs throughout Arkansas and its impact on grain sorghum is similar to that of the corn earworm. This impact occurs in the form of direct damage to seed.

Life History

In early spring adults migrate into Arkansas from more southern states, mate and seek suitable host plants for egg laying. Eggs are laid in masses that contain up to a few hundred eggs. Emerging larvae feed for two to three weeks and then pupate just below the soil surface. Multiple generations occur each year.

Management

Lepidopterous caterpillars often feed within the heads of grain sorghum and visual examination of the head my not detect all larvae. By shaking the seed head over a white bucket, the larvae will be dislodged and can be more easily counted. At least 30 plants per 80 acre field should be sampled. Thresholds for caterpillars on grain sorghum heads vary greatly due to the profit potential of the crop. In general when lepidopterous caterpillars (corn earworm, fall armyworm and sorghum webworm) number two or more per head in grain sorghum nearing maturity foliar insecticides may be warranted. Use of foliar insecticides to reduce damage may not produce economic benefits and should only be used against high insect populations. Numerous beneficial organisms affect fall armyworm including naturally occurring insect pathogens, parasites and predators and insecticide use may reduce their effectiveness. Fall plowing to destroy and bury crop residue will reduce overwintering populations of armyworm. Finally, “open headed”grain sorghum hybrids better expose caterpillars to foliar insecticide sprays and to beneficial organisms.

Insecticide recommendations for fall armyworm on grain sorghum

See Table 2 for insecticide recommendations current at time of publishing. Current updated recommendations can be found in the Cooperative Extension Service publication MP-144 and on the world wide web at WWW.cdms.net/manuf/default.asp. Always follow instructions on pesticide labels.