Sporadic reports of fall armyworm have emerged in parts of the Corn Belt. While they don’t strike every year, fall armyworms can devastate forages and crops, making late-season scouting crucial.
Fall armyworm, native to tropical regions in the Western Hemisphere, can only successfully overwinter in Southern states. However, adults are strong flyers and capable of long-distance migration to the Midwest. Multiple migrations are possible each summer, and adults can be found in Midwestern states from mid-to-late summer months.
In 2021, an extremely unusual fall armyworm outbreak devastated forages and crops across several states. Farmers should monitor fields, especially forage crop fields, for moths and infestation.
Pioneer Field Agronomist Matthew Montgomery, based in Illinois, said understanding how to identify this pest, its life cycle and effective scouting techniques can help minimize damage and protect yields. Fall armyworm can be differentiated from other similar pests by its distinct physical features:
- Head Capsule: Larvae have a dark head capsule with a noticeable white, inverted “Y” between the eyes.
- Tail Segment: Look for four small dots arranged in a square pattern on the last segment of the body.
Life Cycle and Potential Damage
“Fall armyworm does not overwinter in colder climates across the Corn Belt,” Montgomery said. “Instead, it migrates from the Gulf Coast each season, spreading across North America. It can produce multiple generations in a single growing season, increasing its potential to cause damage.”
Fall armyworm can affect alfalfa, corn and soybeans. In corn, it can feed on ears, often beneath the husk. This feeding behavior makes it difficult to control with insecticides, as the larvae are protected by the husk.
In soybeans, fall armyworm can cause defoliation. While rare, it’s important to monitor fields closely, especially during the pod fill stage (around R5.5). Significant leaf loss (about 15% across the field) may warrant an insecticide application.
Scouting Techniques
One effective scouting technique for detecting fall armyworm is the “beat and count” method:
Beat Method: Kneel, grab the foliage on either side and vigorously beat the plant toward the center. This action will dislodge any larvae, making it easier to spot them on the ground. Laying a white or tan cloth on the ground before beating the foliage will make it easier to count and assess the infestation level.
