Plant Bugs in Alfalfa
Published: 01/20/2023
Crop Injury: The pale legume bug (Lygus elisus), western tarnished plant bug (L. hesperus), tarnished plant bug (L. lineolaris), and the alfalfa plant bug (Adelphocoris lineolatus) are the four primary plant bugs that feed on alfalfa in the United States and Canada. Plant bugs use piercing-sucking mouthparts to feed on plant sap. Alfalfa grown for seed is generally considered to be at higher risk of plant bug injury than forage alfalfa. Symptoms on alfalfa grown for seed include seed shrivelling, abscission of flowers, and flower bug blasting. Forage alfalfa quantity and quality can be reduced; other symptoms in forage alfalfa include delayed regrowth, stunting, tissue yellowing or reddening, distortion and death of foliage, and stem length reduction.
Pest Description: Plant bugs have a triangle or “v” shape near the middle of their backs at the wing base. Nymphs are greenish in color and lack fully developed wings. Pale legume bug adults are dark green with greenish forewings. Western tarnished and tarnished plant bug adults have dark marks on a tan to brownish body; their wings range from green to dark brown, and are often reddish. Alfalfa plant bug adults are larger than lygus bugs, have a dark spot over each “shoulder” on the thorax, greenish bodies, and yellowish-green, tan, and/or brown wing coloration.
Tarnished plant bug
Iowa State University Integrated Pest Management Program
Alfalfa plant bug
Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Life Cycle: Plant bugs overwinter as eggs (alfalfa plant bug) or adults (the three Lygus spp.). After hatching, plant bugs develop through multiple instars before reaching adulthood. Multiple generations can occur per year, depending on region and species.
Scouting: Use a sweep net to sample for plant bugs. Symptoms on forage alfalfa can resemble those caused by the potato leafhopper.
Using a Sweep Net in Alfalfa
Management: Early spring stubble burning can reduce overwintering alfalfa plant bug eggs. Insecticide use may be warranted if high alfalfa plant bug populations exist. Be aware that insecticide use can kill important natural enemies and pollinators. Early harvest may eliminate the need for insecticide application. Insecticides are generally not economically beneficial when used for management of pale legume bug, western tarnished plant bug, and tarnished plant bug in forage alfalfa.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Tarnished plant bug
Alfalfa plant bug. Scott Bauer, USDA Agricultural Research Service, Bugwood.org.
Lygus bug
Pale legume bug. Whitney Cranshaw, Colorado State University, Bugwood.org.
Tarnished plant bug. Scott Bauer, USDA Agricultural Research Service, Bugwood.org.
Alfalfa plant bugs. Howard F. Schwartz, Colorado State University, Bugwood.org.
Gallery images courtesy Laura Iles, Iowa State University Integrated Pest Management Program, Scott Bauer, USDA Agricultural Research Service, Bugwood.org, Whitney Cranshaw, Colorado State University, Bugwood.org, and Howard F. Schwartz, Colorado State University, Bugwood.org.
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