Figure 1. Tarnished plant bug adult. Credit: A. Varenhorst
While scouting pea fields last week, we noticed some populations of tarnished plant bugs. Although these insects are rarely an issue in most crops, they can cause considerable damage to field peas due to pod feeding. Low numbers of tarnished plant bugs are commonly found in field peas, lentils, alfalfa and other row crops. However, their populations can dramatically increase when a nearby crop, such as alfalfa, is harvested.
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 light green color. The nymphs will have wing pads, but will not have fully developed wings.
Scouting & Thresholds
Both the tarnished plant bug nymphs and adults can be scouted by using a 15-inch sweep net. With the sweep net, walk in a “Z” pattern throughout the field. Using 180 degree or pendulum sweeps, swing the net for a total of 10 times on each leg of the pattern and count the number of tarnished plant bugs present. 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.
Associated Damage & 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 to the developing seed. When tarnished plant bugs feed on pods they often cause discoloration of the seeds that is referred to as chalk spot. Seeds that have been fed on by tarnished plant bugs will often appear shriveled or otherwise deformed. The seeds that have chalk spot will have a white area of the seed that is depressed and looks similar to a crater. The presence of chalk spot can lead to quality issues when the seed is marketed. For a list of currently available insecticides, please refer to Table 1. Management of tarnished plant bugs should occur prior to pod feeding. When applying insecticides be aware of the pre-harvest interval that is associated with the product.
Table 1. Insecticides available for tarnished plant bug management in field pea*.
|Pre-Harvest Interval (Days)|
(chlorantraniliprole + lambda-cyhalothrin)
|Brigade 2EC, Fanfare2EC, Tundra EC
(bifenthrin + zeta-cypermethrin)
|Karate, Warrior II, Grizzly, Silencer
|Renounce 20WP, Tombstone, Tombstone Helios
|*This list is not intended to be comprehensive. Always follow label instructions when applying insecticides.|