The adult tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is about 1/4 inch long and is brown with yellowish and black dashes and a brassy appearance. The adults overwinter in protected places. They return to the field about the time of bud burst and are found feeding on tender foliage of all sorts. They are very active, taking to flight with the slightest disturbance. Several generations hatch each year; adults and nymphs of all stages can be found from April until heavy frost in the fall.
As a strawberry pest, the tarnished plant bug often causes considerable loss by feeding on the seeds of the young fruits before the receptacle expands. In feeding, it sucks out plant juices. The damaged seeds cause the receptacle to expand unevenly. Thus, berries that are injured remain small, have a woody texture, and fail to mature. Berries become knobbed with seeds grouped apically and are unsalable. This injury is known as "button berry" and is a serious problem in some areas. Later-maturing varieties are more severely affected. Although several plant bugs (Lygus spp. and others) may be involved, the tarnished plant bug appears to be the chief culprit.
Small, underdeveloped berries can be caused by other factors, most notably poor pollination; however, fruits that are small due to poor pollination will not have developed seeds, but instead will have small, hollow, hair-like projections where the seeds should be. If the deformed berry has developed seeds, it probably has sustained plant bug injury.
An insecticide application might be necessary if nymphs are present just before bloom. Growers also should sample fruit clusters on a weekly schedule when fruit begins to form. Shaking flower and fruit clusters over a light-colored plate will dislodge bugs and allow them to be seen more easily. When an average of 20 to 25 bugs per 50 flower clusters is found, spraying is advisable.