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Scout for Lygus Bugs in Pulse Crops (06/30/16)

Tarnished plant bug, Lygus lineolaris, is one of the more common species of Lygus bugs and is known to feed on over 385 crops and weed plants.

Scout for Lygus Bugs in Pulse Crops

Tarnished plant bug, Lygus lineolaris, is one of the more common species of Lygus bugs and is known to feed on over 385 crops and weed plants. Adult Lygus bugs are about ¼ inch in length, and pale green, light brown, or dark brown with a distinctive triangular marking on its back.

Low numbers of Lygus bug, only 1-3 per 25 sweeps, are being found in field peas and lentils in NW ND (Burke, Divide, McKenzie, Mountrail, and Williams counties) (Source: NW Pulse Crop Survey, Adam Carlson & Dr. Kalil).

Lygus bugs overwinter as adults in weedy areas under debris along fence rows, ditches and roadsides. Adults emerge in early spring, lay eggs in the stems, leaves and flowers of host plants, and then die. Immature nymphs hatch from these eggs and look like aphids. Several generations occur each year with the second generation occurring in mid-July to early August. As with many other insect pests, warm, dry weather favors the buildup of Lygus populations and increases the potential for early season damage to peas or lentils. Both immature and adult Lygus bugs feed on developing pods and seeds of peas and lentils, and have been linked to “chalk spot.”

Damage is caused by the piercing-sucking mouthpart, which punctures the pods and seed coats injecting a toxic substance into plant parts. Chalk spot is a pit or crater-like depression in the seed coat with or without a discolored chalky appearance. Damage seeds are smaller, deteriorate faster in storage, have poor germination, and produce abnormal seedlings as well as lower the grade and marketability. It is important not to confuse damage caused by Lygus bug to damage caused by rough harvesting or handling. For example, peas harvested at high moisture levels are also susceptible to bruising when harvested or handled roughly, resulting in damage similar to chalk spot.

Monitor for Lygus bugs using a 15-inch sweep net during bloom to pod development (until seeds within the pod have become firm). Make ten 180 degree sweeps at five sampling sites in a field during the warm sunny part of the day (2-6 PM). Lygus populations can increase suddenly. For example, when an alfalfa (preferred host) field is cut, Lygus will migrate quickly into nearby pulse crop fields and often in high numbers. No economic threshold has been determined for this region. However, in the Pacific Northwest, an insecticide treatment is recommended when “10 Lygus per 25 sweeps” are present. Spray a blooming crop when there is minimal bee activity, preferably during the evening hours (after 8 PM).

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Janet J. Knodel

Extension Entomologist

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