While scouting this week we, noticed that there are large numbers of Lygus bugs present in Central South Dakota. Although these insects are generally not an issue for most crops, they can cause serious injury to field peas if pod feeding occurs. Although the scouted pea fields don’t have pods yet, it is important to closely monitor fields as pods begin to develop.
Lygus bugs include several species that are similar to one another. Both the nymphs and adults of tarnished plant bugs will feed on developing plants. However, the two will look different from one another due to variations in color, presence of wings in adults, and size. Adult Lygus bugs are approximately ¼ of an inch long. They are typically green to brown in color and will have distinct white triangular markings present on their back. In addition, the end of their bodies will be depressed (i.e., pointed down) in comparison to the rest of their body (Figure 1). The nymphs are typically light green in color with wing pads present instead of fully developed wings.
Figure 1. Lygus bug adult. Courtesy: Adam Varenhorst.
Scouting and Thresholds
Both the Lygus bug nymphs and adults can be scouted for by using a 15-inch sweep net. With the sweep net, walk in a Z or W 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 and Management
Lygus bugs use their piercing, sucking mouthparts to feed directly on pods and the developing seeds. During feeding, they inject their saliva into the feeding site, which causes further injury to the developing seed. Pod feeding often results in discoloration of the seeds, which is referred to as “chalk spot.” The seeds that have been fed on will be shriveled and otherwise deformed. Seeds with “chalk spot” will have a white area on 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. Management of tarnished plant bugs should occur prior to the occurrence of pod feeding. Table 1 contains a list of insecticides that are labeled for Lygus bug management. When applying insecticides be aware of the pre-harvest interval that is associated with each product.
Table 1. Insecticides available for tarnished plant bug management in field pea*.
(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.