Fall Armyworm (Spodoptera frugiperda)

Introduction
The fall armyworm is native to North, South and Central America. In the United States, it is found throughout the year in warm coastal states along the Gulf of Mexico, but only overwinter in southern Texas and southern Florida. Infestations in other areas are due to migration of the adults each year. The fall armyworm can be found throughout most of the United States east of the Rocky Mountains during the growing season.

Fall armyworm feed on a wide range of broadleaf and grass hosts (estimated more than 80 species). However, grasses are preferred hosts. Some of the crops that are frequently infested include: alfalfa, barley, soybean, sugarcane, corn, oat, millet and cotton. Several weed species including crabgrass, bentgrass and nutsedge are known hosts.

Identification
Larva:

  • 1 1/4 inches long at maturity (3 cm)
  • Three light stripes along back with darker stripe on each side. A wavy yellow-red stripe is located below the dark stripe
  • Color varies from light tan to black
  • Head capsule is dark brown with a prominent white inverted Y
 fall armyworm larva
Image courtesy of Ric Bessin: University of Kentucky

Adult:

  • 1 to 1 3/4 inches wingspan (2.5 to 4.2cm)
  • White spot present near tip of front wing
  • Gray mottled moths
fall army worm adult
Fall armyworm adult

Image courtesy of University of Nebraska: Lincoln

Eggs:

  • 50 to 150 eggs in cluster
  • Covered with scales and bristles
 fall army worm eggs
Eggs of fall armyworm

Image courtesy of Dr. Ron Smith: Auburn University and University of Georgia IPM image website (http://www.ipmimages.org)
Biology
Fall armyworms are unable to overwinter in areas where the ground freezes. However, they do overwinter in southern states as larvae. In the spring, overwintered larvae will pupate and adults emerge. Adults will move northwards until cold weather stops them. Multiple generations can occur. In northern states 1 to 3 generations may occur; in southern states, five or more generations may be found. At night, females deposit eggs on leaves in clusters and cover them with scales.

Larvae will hatch in 2 to 10 days. Newly hatched larvae begin feeding on leaf tissue, eventually moving to squares, bolls, and blooms. Larvae feed for 2 to 3 weeks and then drop to the soil to pupate. New adults emerge in about two weeks. An entire lifecycle from egg to adult can take 30 to 50 days depending on temperature. Fall armyworm may not be found in northern areas until August or September.

 fall armyworm frass
Fall armyworm and frass on corn leaf

Image courtesy of Ric Bessin: University of Kentucky
fall boll damage
Image courtesy of Dr. Ron Smith: Auburn University and University of Georgia IPM image website (http://www.ipmimages.org)
fall armyworm early damage
Image courtesy of Dr. Ron Smith: Auburn University and University of Georgia IPM image website (http://www.ipmimages.org)
Damage
Fall armyworms quickly disperse from the egg mass when they hatch. They are cannibalistic so it is most common to only find one larvae in a bloom, boll or square.

Damage by young larvae to bracts results in etching, producing a windowpane effect similar to beet armyworm damage. However, fall armyworm will not feed on leaf tissue near the egg mass as beet armyworms do. Fall armyworm feed near the base of the developing boll, unlike budworm/bollworm, which feed further up on the boll. Larger fall armyworm larvae are able to bore into bolls. Fall armyworm can be also commonly found feeding in both red and white blooms.

Control
The reduction of insecticide applications following boll weevil eradication has allowed fall armyworm populations to become more common in cotton. Control with conventional insecticides can be difficult, particularly if they have entered a boll. Additionally, because they are often deep in the plant canopy, penetration and coverage are issues. Full rates of conventional insecticides should be used to help ensure efficacy.

When scouting for fall armyworm, it is important to pay close attention to the lower portions of the plant in particularly inside bracts of maturing bolls and both red and white blooms. Treatment recommendations vary by state. Contact your local extension entomologist to determine the treatment thresholds for your area.

Cotton varieties containing WideStrike™ Insect Protection provide season-long protection against fall armyworm. However, it may not be at 100 percent. If larvae reach the flowers prior to ingesting a lethal dose, it is possible for them to reach a size that is difficult to kill. Therefore, it is recommended that scouting for fall armyworms continue. Additionally, use of cotton varieties containing WideStrike allow for reduction in insecticide applications that may help maintain the natural controls to keep the fall armyworm populations below threshold.