Responsible for over 463,000 bushels of yield loss in corn in 2024, fall armyworm (Spodoptera frugiperda) can cause significant damage to U.S. corn crops.¹ Here’s an overview of how to scout, identify and manage fall armyworm.
Lifecycle of fall armyworm
The fall armyworm life cycle can span 30 to 90 days, depending on temperature. It moves through six larval stages, called instars, reaching up to 1 1/2 inches long at maturity. Most damage from fall armyworm occurs in the larval stage, which can last from two weeks to a month, depending on temp. Larvae can burrow into the growing point and the ears, often leaving plant leaves nearly shredded. After the larval stage, the caterpillar burrows underground and becomes a pupa (a nonfeeding stage). It emerges as an adult moth two weeks later, then begins reproducing. Females deposit eggs onto leaves, and the cycle begins anew.
Identifying fall armyworm
Fall armyworm eggs look like a small, grayish-white cloud filled with up to 200 pale eggs, each less than half a millimeter in size. Look for eggs adhered to the underside of leaves, close to the base of the plant near the point where the leaf meets the stem. The first instar of the fall armyworm caterpillar is light green with a black head. In the second instar, the head is orange-tinged. By the third, the larva’s back is tan-brown, and white stripes run along its sides. In the final stage, its head, now mostly dark brown-red, bears a light mark in the shape of an inverted Y. This unique mark helps differentiate the fall armyworm from similar-looking pests, such as true armyworm and corn earworm. The mature fall armyworm also has four dark spots arranged in a square on its second-to-last abdominal segment.
At the pupal stage, the fall armyworm is red-brown, capsule-shaped and less than an inch long. The adult moth has a wingspan of around 1 1/2 inches, with brown-gray forewings (marked with white patches in the male) and white-silver hindwings with a thin dark border.
Early fall armyworm damage resembles a “windowpane” pattern of foliar damage — small, translucent patches of leaf tissue caused by early-stage larvae nibbling away the outer layer of the leaf tissue. Damage caused by more mature caterpillars ranges from holes in leaves, often beginning at the outer edge of the leaf and proceeding inward, to large-scale defoliation and feeding on kernels.
Scouting for fall armyworm
Begin scouting by mid-June in the Midwest. Scout in early morning or late afternoon when larvae are most active. Examine 20 plants in five random field locations, looking for signs of larvae and leaf damage. Estimate the percentage of infestation from the 100 plant samples.
Managing fall armyworm in corn
Managing fall armyworm in corn involves paying careful attention to seed selection and the planting schedule, and using scouting results to assess and apply treatment options.
Planting timing and seed selection: Fall armyworm infestations become denser throughout the growing season as early planting and early-maturing hybrids can help mitigate fall armyworm damage. Certain Bt corn hybrids offer effective management of fall armyworm.
Insecticides for fall armyworm in corn: Insecticide treatment is effective only in the early stages of armyworm infestation. Insecticide applications are typically recommended when 75% or more of plants are infested (showing damage from feeding in the whorl) and the caterpillars are not yet longer than 1 1/4 inches. FASTAC CS is labeled for use against fall armyworm in corn.
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
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Endnotes
- “Corn Invertebrate Loss Estimates from the United States and Ontario, Canada — 2024.” Crop Protection Network, 17 Feb. 2025, cropprotectionnetwork.org/publications/corn-invertebrate-loss-estimates-from-the-united-states-and-ontario-canada-2024. Accessed 26 Feb. 2026.
