By Adam J. Varenhorst
During a visit to field pea we observed the presence of several insects, including the tarnished plant bug. This insect is also referred to as the Lygus bug. Although the field we were sampling was below the recommended threshold, it is important to monitor tarnished plant bug populations. Populations of tarnished plant bug in field pea can increase very rapidly due to their presence in other crops that may be harvested prior to field pea, which ultimately forces the tarnished plant bugs to seek new hosts.
Tarnished Plant Bug Identification
The tarnished plant bug nymphs and adults look quite different from one another. The adults are approximately ¼ of an inch in length, and may vary in color from green to brown. They can be identified by the distinct white triangular markings that are present on their back. In addition, the end of the abdomen of adult tarnished plant bugs is depressed when compared to the rest of the body (Figure 1). Tarnished plant bug nymphs are slightly smaller than adults, and are typically a lighter green color without wings.
Figure 1. Tarnished plant bug adult. Photo courtesy of Russ Ottens.
Scouting & Economic Thresholds
Tarnished plant bug nymphs and adults can be scouted by using a 15 inch sweep net. With the sweep net, walk in a “W” or “Z” pattern throughout the field. Using 180 degree or pendulum sweeps, swing the net for a total of 10 times and count the number of tarnished plant bugs present. Repeat this process for each leg of the walk. The economic threshold for sweep netting tarnished plant bugs is 4 bugs per 10 sweeps. If this threshold is exceeded throughout the field after pod formation has begun insecticide management should be considered.
Crop Injury & Pest Management
Tarnished plant bugs use their piercing sucking mouthparts to feed directly on pods and the developing seeds within. During feeding, the tarnished plant bugs inject their saliva into the feeding site, which causes further injury due to a toxin present in the saliva. When tarnished plant bugs feed on pods they often cause discoloration of the seeds that is referred to as “chalk spot”. Often seeds that have been fed on by tarnished plant bugs will be shriveled and otherwise deformed. The seeds that have “chalk spot” will have a white area of the seed that is depressed similar to a crater. The presence of “chalk spot” can lead to quality issues when the seed is marketed. For insecticides available for managing tarnished plant bugs please refer to Table 1.
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