Scouting For Tarnished Plant Bug In Sunflower

By Adam J. Varenhorst

Assistant Professor & SDSU Extension Field Crop Entomologist

Tarnished plant bug, or Lygus bug, is an economically important pest of confection sunflower seeds. Feeding injury from the tarnished plant bug’s piercing-sucking mouthparts causes characteristic dark spots on seeds, often referred to as kernel brown spot. Damaged seeds not only appear discolored, but have an unpleasant flavor after roasting. Feeding occurs primarily on developing seeds during the sunflower bloom stages (R5). Additionally, tarnished plant bug injects saliva into the feeding site, which can promote necrosis or brown spot.

Tarnished Plant (Lygus) Bug Identification

Adult tarnished plant bugs are approximately 1/5 of an inch long, and may vary in color from tan to black. Although the adults vary in color, they all have distinctive white and yellow markings present on their bodies (Figure 1). Another useful characteristic for identification are the yellow triangles present on the ends of each front wing. Because tarnished plant bugs fold their wings over the bodies, these yellow triangles appear on each side of their bodies near the end of the abdomen. The end of the abdomen is depressed, and appears to be pointing towards the ground. Tarnished plant bug nymphs are smaller than the adults and green to yellow-green in color. They are more teardrop shaped than the adults.




Figure 1. Tarnished plant bug adult. Photo by Adam Varenhorst.
 
Scouting and Management

To scout for tarnished plant bugs in sunflower, examine nine random plants from three locations throughout the field for a total of 27 plants per field. For each plant, look at the sunflower head and leaves for tarnished plant bug adults. Record the number of adults and calculate the average number observed per nine plants. The economic threshold for tarnished plant bugs is one adult per nine heads. Research has shown that one tarnished plant bug per 10 heads is capable of causing damage that results in issues when marketing the seeds.