Yellowstriped Armyworm in Soybean
Crop Damage
The yellowstriped armyworm (Spodoptera ornithogalli) occurs throughout the United States, from the East Coast to the Midwest, and in southern regions including Arizona, New Mexico, Texas, and southern California, as well as in Mexico. Larvae have a broad host range, feeding on vegetables, forage crops, and soybeans. In soybean, early instars feed on the underside of leaves between veins, producing a skeletonized appearance, whereas older larvae consume entire leaves.
A similar species, the western yellowstriped armyworm (S. praefica), may be confused with S. ornithogalli. This species is restricted to western coastal states and southern British Columbia, Canada. It feeds on alfalfa, forage crops, vegetables, ornamental plants, and weeds, but is not currently considered a pest of soybean.
Yellowstriped armyworm damage. Orange arrow indicates spot above middle true legs.
Adam Sisson, Iowa State University
Pest Description
Full-grown larvae reach up to 2 inches long and vary in color (cream, brown, gray, or black). A distinguishing feature is the presence of distinct yellow longitudinal bands along both sides of the body, often accompanied by lighter stripes below. Dark triangular markings may occur along the dorsal surface of each segment, and a dark spot may be present below the yellow bands and above the middle pair of true legs. The head capsule is dark with a characteristic cream-colored inverted “Y.” Adult moths exhibit cream, brown, and black wing patterns, including a distinct cream-colored “V” shape and a pale band across the middle of each forewing.
Scouting
Yellowstriped armyworms are often associated with alfalfa and may move into adjacent soybean fields, particularly following alfalfa cutting. Begin scouting at field edges and expand sampling across the field if larvae are detected. Use multiple, randomly selected sampling locations to estimate whole-plant defoliation accurately, with additional sites in larger fields. The Crop Protection Network’s Insect Defoliation Tool can assist with defoliation estimates.
Management
If infestations are confined to field edges, spot insecticide treatments may be sufficient. For field-wide infestations, treatment thresholds are 30% defoliation during vegetative stages and 20% during reproductive stages. Consider cumulative injury if multiple defoliators are present. Biological control agents, including minute pirate bugs, damsel bugs, parasitoid wasps, parasitic flies, and viral pathogens, may contribute to population suppression. For current management recommendations, consult your local extension specialist.
Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.
Yellowstriped armyworm damage. Orange arrow indicates spot above middle true legs. Adam Sisson, Iowa State University
Yellowstriped armyworm. Orange arrow point to the spot above the middle true legs. Blue arrows point to the dark triangles on each segment. Adam Sisson, Iowa State University
Yellowstriped armyworm. Orange arrow points to the spot above the middle true legs. Blue arrows show the dark triangles on each segment. Whitney Cranshaw, State University
Yellowstriped armyworm moth. Orange arrow points to the “V” shape Blue circle shows the forewing band. Robert J Bauernfeind, Kansas State University
Gallery images courtesy of Adam Sisson, Iowa State University; Whitney Cranshaw, Colorado State University, Bugwood.org; and Robert J Bauernfeind, Kansas State University, Bugwood.org.
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