Black Cutworm in Soybean
Crop Damage
The black cutworm (Agrotis ipsilon) occurs throughout the United States, Mexico, and southern Canada. Larvae feed on multiple crops, including soybean seedlings. Early instars damage the plant base by feeding on lower leaves and stems. Later instars can sever entire plants, causing stand loss, and may cut several plants in a single night.
Black cutworm.
Adam Sisson, Iowa State University, Bugwood.org
Pest Description
Full-grown larvae reach approximately 2 inches long and have light gray to black, grainy-textured skin. A key identification feature is the presence of dorsal tubercles on each body segment; the anterior pair is smaller than the posterior pair. Adults are medium to dark brown moths with a small black dagger marking on each forewing.
Scouting
Pheromone trap networks, where available, can help determine when to begin scouting. Black cutworms should be monitored weekly until plants reach the V5 stage. High-risk fields include late-planted areas, fields with crop residue, weedy borders, or low-lying zones. Inspect for wilted, discolored, cut, or dead plants. To confirm cutworm presence, carefully dig around the base of damaged plants. Sample 20 plants in five high-risk areas to estimate the percentage of cutworm damage.
Management
Insecticide treatment thresholds vary by state and are influenced by commodity prices and application costs. Recommended thresholds generally range from 10% to 30% of plants damaged with confirmed cutworm presence. Replanting may be necessary if stand loss is substantial. For updated 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.
Black cutworm. Adam Sisson, Iowa State University, Bugwood.org
Orange arrows indicate the different size tubercles. Adam Sisson, Iowa State University.
Black cutworm adult. Arrow indicates dagger on forewing. Mark Dreiling, Bugwood.org
Gallery images courtesy of Adam Sisson, Iowa State University, Bugwood.org and Mark Dreiling, Bugwood.org
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