Corn Earworm in Soybean
Published: 04/10/2026
Crop Damage
The corn earworm (Helicoverpa zea) occurs throughout the United States and southern Canada. While commonly associated with corn, it can be a significant pest in soybean. Larvae feed on leaves, flowers, and pods, with older larvae capable of penetrating pod walls and consuming seeds, causing the greatest economic damage.
Pest Description
Full-grown larvae are approximately 1½ inches long and vary in color (brown, green, orange, purple, or yellow). Distinguishing characteristics include alternating longitudinal stripes, small tubercles each bearing an erect hair, and four pairs of abdominal prolegs. The head is typically orange but may also be green or brown. Adult moths have a dark spot near the center of each forewing, and hindwings exhibit a dark marginal band.
Corn earworm larvae with variable coloration.
Ashley Dean, Iowa State University
Scouting and Management
Moth arrival varies by region and season. Where available, pheromone trap networks can help determine when to begin scouting. In the absence of traps, initiate weekly scouting during late vegetative stages prior to flowering. High-risk factors include late-maturing varieties and wide row spacing, which favor egg-laying in open canopies. Three primary sampling methods are recommended:
Sweep net: Take 25 sweeps at four or more locations and count the average number of larvae per location. The treatment threshold is 8 larvae per 25 sweeps (based on $11/bushel soybeans and $25/acre control cost).
Drop cloth: At 10 field locations, place a 6-foot white sheet between rows and shake plants to dislodge larvae. Record the average number per row foot. The treatment threshold is 2 larvae per row foot (same economic basis as above).
Plant defoliation estimates: Randomly sample plants across the field to estimate whole-plant defoliation and pod injury. Use the Crop Protection Network’s Insect Defoliation Tool for an accurate assessment. The treatment threshold is 30% defoliation in vegetative stages and 20% in reproductive stages.
Corn earworm has demonstrated resistance to some pyrethroid insecticides. Insecticide applications may also impact beneficial organisms. Natural enemies include predatory and parasitic insects, parasitoid nematodes, and pathogens. Cultural practices—such as adjusting planting dates, selecting early-maturing varieties, and optimizing row spacing—can reduce infestations.
For updated sampling methods, treatment thresholds, and management recommendations, consult your local extension specialist.
Prepared and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.
Corn Earworm Economic Threshold Calculator (North Carolina State University Extension).
Corn earworm larvae with variable coloration. Ashley Dean, Iowa State University
Corn earworm larva feeding on pod. Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Corn earworm larvae with stripes, tubercles with hairs, and orange arrows indicate characteristic prolegs. Adam Sisson, Iowa State University.
Corn earworm moth. Orange arrows indicate dark spot on forewings. Ashley Dean, Iowa State University.
Corn earworm moth Orange arrows indicate dark spots on forewings. Blue arrows indicate dark bands on hindwings. Adam Sisson, Iowa State University
Gallery images courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org; Ashley Dean, Iowa State University; and Adam Sisson, Iowa State University
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