Tarnished Plant Bugs, Other Plant Bugs, and Stink Bugs
Description and life cycle
Tarnished plant bug adults are about ¼ inch long, oval, fragilelooking insects, green to dark brown, flecked with white, yellow, reddish brown, and black markings. Nymphs are pale yellow to green. Stink bugs are broadly shield-shaped, flattened, with a narrow head and rather short legs, and are green to brown. All have the front half of the forewing leathery and the back half membranous. Mouthparts are the piercing-sucking type; the beak is three- or four-segmented, arises on the front of the head, and is held below the body, between the legs, when not in use. Antennae are usually long and four- or five-segmented. Compound eyes are normally large. Nymphs (immature stage) are generally similar to adults but do not have wings.
These bugs feed by sucking sap from plants. They are believed to inject a toxic substance into the plant when feeding to break down plant tissues. Their feeding is very destructive to fruit and other tender plant parts. On apples tarnished plant bugs feed on developing fruitlets and cause dimpling. Earliest injury to peaches is caused by tarnished plant bugs, other Lygus spp., and possibly stink bugs, which are active in the early spring. Tarnished plant bugs often cause the most damage, because they are normally present in high numbers when peaches start to grow. They feed on swelling fruit and leaf buds, causing the buds to dry up. When fruit buds are damaged, blossoms may never open or may be deformed. Later, feeding on open blossoms or small fruit usually causes the damaged blossoms or fruit to fall. If damaged peaches do not fall, they become scarred and malformed (catfacing injury) as they grow. Cold weather or hail may cause similar injury. Tarnished plant bug feeding on young, tender, terminal or lateral shoots can also cause wilting and dying back, sometimes giving young trees a brushy appearance.
Most severe catfacing damage is done immediately following bloom, from petal fall until peaches are ½ to ¾ inch in diameter. Cells are destroyed and fruit development inhibited at the feeding site, while surrounding tissues continue to grow and expand. As peaches increase in size, feeding by plant bugs or stink bugs causes less scarring and distortion of the fruit. When mature or nearly mature, peaches are attacked, primarily by stink bugs. Beads or strings of gum may exude from the feeding site and shallow, dry, corky, sunken areas may develop. Peaches on the edges of orchards bordering woodlands, fence rows, or fields are usually the first and most severely damaged.
These bugs overwinter as adults in protected places, such as in ground debris or between the leaves of various plants. A newly introduced species of stink bug—brown marmorated stink bug, Halyomorpha halys (Stäl)—will attempt to overwinter inside houses or other buildings. Many may become active periodically on warm days during the winter. Time of emergence from hibernation in the spring varies with species, but most bugs emerge in early spring.
Tarnished plant bugs are often present in peach orchards by the time buds begin to swell. They feed on the flower buds of peach trees and numerous other plants. They are strongly attracted to orchards with winter annual weeds in bloom. Egg laying begins shortly after adults emerge, most eggs being laid in the tender shoots or flower heads of herbaceous weeds, vegetables, and legumes. Few eggs are laid in peaches. Eggs hatch in about 10 days and emerging nymphs begin to feed. The nymphal stage lasts about a month. There are several generations of tarnished plant bugs each year, but the bugs normally begin to leave peaches shortly after petal fall and move to other hosts. Populations in peach trees usually decline significantly by shuck fall.
Stink bugs feed throughout the growing season. They have one or two generations per year, depending on species. In recent years, brown marmorated stink bug was observed in eastern Pennsylvania feeding on vegetables, fruit, and ornamental trees.
Plant bug and stink bug populations may be monitored by trapping, sampling, and fruit survey. Trapping is most successful in apple where visual sticky white cards are hung out about two feet from the ground from an outer branch at silver tip and checked weekly. Traps should be placed at the edge of the block at one per three to five acres. The economic injury level is 2.4 adults per trap by tight cluster and 4.1 per trap by late pink. Monitoring in peaches and nectarines is critical at petal fall to shuck fall. Sweep net sampling of blooming ground cover in sections of orchards bordering woodlands, fencerows, or other favorable hibernation sites is used to indicate populations that can move into the trees. Two hundred fruit should be checked periodically per block to pick up fresh feeding.
Preventing broadleaved winter annual weeds and legumes in and around orchards can reduce the populations of these bugs. Legumes such as clover and vetch should be avoided as cover crops. Good control of early blooming broadleaved weeds may improve the performance of catfacing sprays.
Preventing serious catfacing injury depends largely on well-timed, early season insecticide applications. On pome fruits critical timings are pink and petal fall. On stone fruits applications at petal fall, shuck fall, and 10 days after shuck fall typically provide good control. Applications during pink are often unnecessary because most fruit injured at this time aborts. Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener, and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide.