The tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), is found in agricultural and disturbed areas throughout the United States. It has one of the broadest host ranges of any insect pest, feeding on 385 plants, 75 of which are economically important crops. Tarnished plant bug has reached key economic pest status in several crops, including strawberry and cotton, and can be responsible for significantly reducing yields in apple.
Adult tarnished plant bugs are approximately 6 mm (¼”) in length, oval and flattened. They are brownish in color with reddish-brown markings on the wings and a characteristic small yellow triangle located in the center of the back.
Tarnished plant bug nymph (Scott Bauer, USDA Agricultural Research Service, Bugwood.org )
Young nymphs are tiny and light green in color. Older nymphs are larger, with 5 noticeable black dots on their back, and well-developed wing pads.
Tarnished plant bugs overwinter in surface leaf litter as adults. In the spring, adults become active when temperatures reach and remain around 49°F, at which time they begin laying eggs in suitable host plant tissue. Nymphs hatch 6-8 days later and can immediately begin feeding. There are multiple generations each year.
Tarnished plant bug damage to apple is caused both by feeding and egg laying. Tarnished plant bugs feed with piercing-sucking mouthparts, extracting plant sap and injecting digestive enzymes, both of which interfere with plant growth. Feeding starts at the silver tip stage of bud development, but the majority of feeding occurs from the green tip stage through petal fall. Feeding prior to the pink stage will cause the bud to fall off, whereas feeding after pink stage results in dimpled fruit. The damage to fruit caused by egg laying often results in more pronounced, or deeper, dimples.
Tarnished plant bug populations can vary from year to year and in some regions are largely dependent on management practices of surrounding areas. For example, in orchards surrounded by alfalfa, if the cutting coincides with the susceptible plant stages in apple, tarnished plant bugs will likely migrate into the orchards. However, if fields are not cut, tarnished plant bugs may instead remain in the alfalfa. Therefore, it is imperative to monitor the flight of tarnished plant bug throughout the susceptible stages of crop growth.
White sticky traps can be an effective tool for monitoring tarnished plant bug adults. Traps should be placed in trees so they are two feet above the ground. Within each orchard block place 3-5 traps/acre, paying particular attention to the edge of the block. Traps should be in the orchard at or before the silver tip stage. Check traps weekly. The current action threshold (point at which a control measure is taken) is 3 to 4 tarnished plant bugs/trap by the tight cluster stage or 5 tarnished plant bugs/trap by the late pink stage.
Controlling weeds is a major factor in reducing tarnished plant bug populations because these insects can both feed and reproduce on weedy plant species. Elimination of weeds and leaf litter also removes potential overwintering sites used by the adults. In addition, several insecticide options are available for tarnished plant bug in apple. Please consult your local production manual for recommendations suitable to your area.
Suzanne Wold-Burkness, University of Minnesota
Daniel Frank, West Virginia University