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Scout for Lygus Bug (07/16/20)

Lygus bugs infestation have been reported in canola in north central North Dakota (T.J. Prochaska, NCREC) and sugarbeets in Red River Valley (M. Khan, NDSU).

Lygus bugs infestation have been reported in canola in north central North Dakota (T.J. Prochaska, NCREC) and sugarbeets in Red River Valley (M. Khan, NDSU). Adult Lygus bugs are about ¼ inch in length, and pale green, light brown, or dark brown with a distinctive triangular marking. Nymphs are smaller than adult, green, and very active when disturbed. The second generation that occurs in late July to early August is usually the most economic population. When alfalfa, a preferred host, is cut, Lygus bugs will migrate quickly into nearby field crops and often in high numbers. Hot dry weather favors the buildup of Lygus populations and increases the risk of damage to field crops. Field crops infested by Lygus bug include canola, sugarbeets, confection sunflowers, and pulse crops (chickpeas, field peas and lentils).

Both nymphs and adults feed on growing points, buds, flowers, and green pods of field crops. Lygus bugs inject a toxic saliva with their piercing sucking mouthparts during feeding, causing curling and wilting of leaves, feeding scars on leaf petioles, blasting of flowers or buds and shriveled seeds in pods. The small, damaged seeds are often lost during harvest.

Economic thresholds vary for the different field crops. 

  • Canola:  15 Lygus bugs per 10 sweeps from bud stage through petal drop, and

20 Lygus bugs per 10 sweeps after petal drop (adults and nymphs combined). If populations are high, control during the early pod ripening stage is usually economical.

  • Forage:  3 to 5 Lygus bugs per sweep (adults and nymphs combined)
  • Pulse crops:  10 Lygus bugs per 25 sweeps (adults and nymphs combined)
  • Sugarbeet:  1 Lygus bug per plant (adults and nymphs combined) and if the crop is at least three weeks from harvest
  • Confection Sunflower only:  1 adult Lygus bug per 9 heads

Janet J. Knodel

Extension Entomologist

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