Beet Armyworm in Soybean
Crop Damage: The beet armyworm (Spodoptera exigua) is a global pest of more than 90 plant species. In soybean, young larvae form clusters and skeletonize the leaves. As they develop, larvae eat large irregular holes in leaves, and older larvae may feed on all parts of the plant.
Beet armyworms in a small cluster.
Michasia Dowdy, University of Georgia, Bugwood.org
Beet armyworm feeding causes irregular holes in leaves.
Whitney Cranshaw, Colorado State University, Bugwood.org
Pest Description: Early instars are light to medium green. By the third instar, larvae develop pale yellow and green stripes along the sides of the body. A distinguishing characteristic is a pair of black spots just behind the head. Adults are gray-brown moths with a distinct white spot near the middle of each forewing and light cream hind wings with a distinct brown border along the outer margin.
Beet armyworm larvae. The orange arrow indicates the characteristic black spot behind the head.
John Capinera, University of Florida, Bugwood.org
Beet armyworm adult. Orange arrows indicates white spot on forewing and brown border on hindwing margin.
Robert Bauernfeind, Kansas State University, Bugwood.org
Scouting: Beet armyworms are more persistent during dry conditions and are attracted to weeds such as lambsquarters and pigweed. Inspect field edges, especially where weeds are present. Randomly sample plants throughout the field to estimate defoliation levels over the whole plant and percentage of plants with stem or pod damage. Use the Crop Protection Network’s Insect Defoliation Tool to accurately assess defoliation.
Management: No specific economic thresholds have been established for beet armyworm in soybean. Young larvae primarily defoliate leaves, while older larvae may injure stems, flowers, and pods. Apply the standard soybean defoliation thresholds – 30% during vegetative stages and 20% during reproductive stages – while considering additional injury to other plant parts. If other defoliating insects are present, assess their combined impact before making management decisions. Although natural enemies of been armyworm have been identified, their overall effectiveness remains unclear. Use of broad spectrum insecticides early in the season before thresholds are reached can decrease beneficial predatory and parasitic insects that help control beet armyworm.
Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.
Several green beet armyworms in a small cluster on a leaf. Image by Michasia Dowdy, University of Georgia, Bugwood.org.
Beet armyworm feeding causes irregular holes in leaves. This image shows a single green beet armyworm on a leaf that shows irregular feeding holes and insect frass. Whitney Cranshaw, Colorado State University, Bugwood.org.
Two green beet armyworm larvae on a green leaf with missing leaf tissue from caterpillar feeding. The orange arrow indicates the characteristic black spot behind the head. Image by John Capinera, University of Florida, Bugwood.org.
Beet armyworm adult moth with an orange arrow indicating a white spot on the forewing and a brown border on the hindwing margin. Image by Robert Bauernfeind, Kansas State University, Bugwood.org.
Gallery images by Michasia Dowdy, University of Georgia, Bugwood.org, Whitney Cranshaw, Colorado State University, Bugwood.org, John Capinera, University of Florida, Bugwood.org, and Robert Bauernfeind, Kansas State University, Bugwood.org.
This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel. This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.
In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.
Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the State or local Agency that administers the program or contact USDA through the Telecommunications Relay Service at 711 (voice and TTY). Additionally, program information may be made available in languages other than English.
To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at How to File a Program Discrimination Complaint and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by: (1) mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue, SW, Mail Stop 9410, Washington, D.C. 20250-9410; (2) fax: (202) 690-7442; or (3) email: program.intake@usda.gov.
This work is supported by the Crop Protection and Pest Management Extension Implementation Program from the U.S. Department of Agriculture’s National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.
USDA is an equal opportunity provider, employer, and lender.
©2025 by the Crop Protection Network. All rights reserved.
