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Scout for Lygus Bug (07/29/21)


Hot dry weather favors the buildup of Lygus populations and increases the risk of damage to field crops like confection sunflowers and canola. Adults are small, cryptically colored insects with a distinctive yellow triangle or “V” on the wings, and are about ¼ inch in length. They vary in color from pale green to dark brown. Lygus bug adults and nymphs insert their mouthparts into developing sunflower seeds or canola pods, and inject a toxic saliva. This causes a brown to black spot called “kernel brown spot” and foul taste in confection sunflowers. In canola, Lygus bug feeding injury causes blasting of flowers or buds and shriveled seeds. Blasted flowers turn white within 24 hours and quickly fall to the ground. The small damaged seeds are lost during harvest.


Adult Lygus bug with nymph in background
Photo Credit:
Whitney Cranshaw, Colorado State University,


Lygus Bug Thresholds

Confection sunflower:                          Oilseed sunflower:

1 adult per 9 heads                                 Not a pest problem


15 Lygus bugs per 10 sweeps from bud stage through petal drop

20 Lygus bugs per 10 sweeps after petal drop


Confection Sunflower scouting: Count the number of Lygus bug adults on 5 plants at 5 sites for a total of 25 plants. Scout for Lygus bugs during flowering. Sunflowers are susceptible from feeding injury during flowering through seed hardening.

Canola scouting: Scout for Lygus bugs from just prior to bud formation until seeds within the pod have become firm. Lygus populations can increase suddenly. For example, when an alfalfa (preferred host) is cut, Lygus will migrate quickly into nearby canola fields and often in high numbers. Use a 15-inch sweep net and make 10 180-degree sweeps at several sampling sites. If populations are high, control during the early pod ripening stage is usually the most economical.



Janet J. Knodel

Extension Entomologist


Patrick Beauzay         

Research Specialist, Extension Entomology