August 2, 2022

Fall Armyworm Identification, Damage Potential, and Management

Fall armyworm (FAW) can appear throughout much of the Midwest in the mid to late summer months. Unable to handle Midwestern cold winter months, FAW moths move progressively north with each generation in the summer from southern states. Each generation can move up to 300 miles.¹

The FAW larva can be identified by shades of green and brown and have a characteristic inverted white “Y” between their eyes (Figure 1). Because several species of larvae can be found feeding on plant tissue in the fall, the “Y” is a defining characteristic for identification.

Figure 1. Characteristic inverted “Y” on head of fall armyworm. Picture courtesy of and used with the permission of Steve L. Brown, University of Georgia, Bugwood.org.

Figure 2. Female fall armyworm moth. Picture courtesy of and used with the permission of Robert J. Bauernfeind, Kansas State University, Bugwood.org.

Damage Potential

Moderate to severe outbreaks can occur, especially in warm years when multiple generations can mature. Late planted crops are attractive because of the tender foliage. During the 2021 growing season, several areas in the Midwest had infestations feeding on alfalfa, soybean, and corn. A unique feature of FAW is the ability to thrive in nearly all crops with more than 60 different plant species recognized as a potential FAW host.³

Management

Cultural, biological, and chemical control measures exist for managing FAW. General management practices include:

Plant early – FAW populations tend to peak in late summer and fall. Moths are attracted to the tender foliage of late planted corn.
Harvest – timely harvesting of hay and other forage crops can help reduce desirable foliage. Larvae can die from the lack of food and exposure to the hot soil surface after hay is removed.³
Scout early and often – Scout along field edges near grass waterways and fence lines for signs of FAW feeding. In corn, begin scouting when corn is near tasseling and silking. Look at plant whorls for feeding and unroll the whorls to make larval counts (Figure 3). Early FAW damage in corn appears as “window paning” and shot holes in leaves; later damage appears as ragged leaves. After feeding on leaf tissue, the larvae move to ears and feed on kernels (Figure 4).
Chemical control – Insecticides are available to help manage FAW if economic thresholds are met. However, larvae feeding within corn whorls may not encounter the insecticide. Additionally, insecticide efficacy is best when the larvae are small. Treatments may be necessary if 75% of the corn plants have whorl feeding and larvae are less than 1 ¼ inches long and the plants are under stress.⁴ Spot treatments can be used if only areas within fields are being damaged.
Trait protection – Protection from fall armyworm feeding can be gained by planting Channel® brand Trecepta® corn (three-mode activity), SmartStax® PRO with RNAi Technology (triple-mode activity), SmartStax® corn (triple-mode activity), or VT Double PRO® corn (dual-mode activity).

Figure 3. Fall armyworm feeding in corn whorl. Picture courtesy of and used with the permission of John C. French, Sr., Retired, Universities of Auburn, Clemson, and Missouri, Bugwood.org.

Figure 4. Fall earworm feeding on corn ear. Picture courtesy of and used with the permission of the University of Georgia, University of Georgia, Bugwood.org.

Zak Swanson

Technical Agronomist

Sources

¹Fall armyworm. Combatting an invasive pest exacerbated by climate change. Bayer Global. https://www.bayer.com/en/news-stories/fall-armyworm-combatting-another-invasive-pest-amidst-the-pandemic/.

²Reynolds, C., Merchant, M., and Reynolds, D.S. Fall armyworms – identification and control. Texas A&M AgriLife Extension. Texas A&M University. https://agrilifeextension.tamu.edu/library/landscaping/fall-armyworms-identification-and-control/.

³Flanders, K.L., Ball, D.M., and Cobb, P.P. 2019. Management of fall armyworm in pastures and hayfields. Alabama A&M & Auburn Universities Extension. Alabama Cooperative Extension System. https://www.aces.edu/blog/topics/farming/management-of-fall-armyworm-in-pastures-and-hayfields/?cn-reloaded=1/.

⁴Fall armyworm. Spodoptera frugiperda Smith. 2009. Field Crops IPM. Purdue University. https://extension.entm.purdue.edu/fieldcropsipm/insects/fall-armyworm.php/.

Web sources verified 6/27/22