Plant Bugs and Stink Bugs
The plant bugs and stink bugs that attack peaches, nectarines, apples, and pears feed on many different wild and cultivated plants, including numerous other horticultural and agronomic crops. They are found in significant numbers throughout Pennsylvania.
Sucking bug pests vary greatly in color, size, and shape but share certain characteristics. The front half of the forewing is leathery, the back half membranous. Mouthparts, arising on the front of the head, are of the piercing-sucking type and are held below the body between the legs when not in use. Antennae are usually long. Nymphs (the immature stage) generally are similar to adults but do not have wings.
The tarnished plant bug, Lygus lineolaris, is a small, oval, fragile-looking, green to dark-brown insect, flecked with white, yellow, reddish-brown, and black markings. Nymphs are pale yellow to green. Adults are about 1/4 inch long.
Stink bugs are broadly shield shaped, flattened, with a narrow head and rather short legs, and are green to brown. They generally are larger than tarnished plant bugs.
Sucking bugs, as the name implies, 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. The earliest injury to fruit is caused by tarnished plant bugs, other Lygus species, and possibly stink bugs, which are active in the early spring. Tarnished plant bugs often cause the most damage because they normally are present in high numbers when fruit starts to grow in the spring. They feed on swelling fruit and leaf buds, causing the buds to dry up. When fruit buds are damaged, blossoms might never open or might be deformed. Later, feeding on open blossoms or small fruit usually causes the damaged blossoms or fruit to fall. If damaged fruit does not fall, it becomes scarred and malformed (catfaced or dimpled) as it grows. Cold weather or hail can cause similar injury. Tarnished plant bug feeding on young, tender, terminal or lateral shoots also can cause wilting and dying back, sometimes giving young trees a brushy appearance.
Most severe catfacing and dimpling damage is done immediately following bloom, from petal fall until fruit are 1/2 to 3/4 inch in diameter. Cells are destroyed and fruit development inhibited at the feeding site, while surrounding tissues continue to grow and expand. As fruit increases in size, feeding by plant bugs or stink bugs causes less scarring and distortion of the fruit. When fruit is mature or nearly mature, it is attacked, primarily by stink bugs. Beads or strings of gum can exude from the feeding site and shallow, dry, corky, sunken areas might develop at the sites of injury. Fruit is usually injured earliest and most severely on the edges of orchards bordering woodlands, fencerows, or fields. Most sucking bugs that attack fruit overwinter as adults in protected places, such as in ground debris or between the leaves of various plants. Many periodically become active on warm days during the winter. Their time of emergence from hibernation in the spring varies with the species, but most bugs emerge in early spring.
Tarnished plant bugs are often present in fruit orchards by the time buds begin to swell. They feed on the flower buds of fruit trees and numerous other plants. They are strongly attracted to orchards that have winter annual weeds in bloom. Egg laying begins shortly after adults emerge, and most eggs are laid in the tender shoots or flower heads of herbaceous weeds, vegetables, and legumes. The eggs hatch in about 10 days, and the emerging nymphs begin to feed. The nymphal stage lasts about a month. Several generations of tarnished plant bugs hatch each year, but the bugs normally begin to leave the fruit shortly after petal fall and move to other hosts.
Stink bugs feed at almost any time during the growing season. One or two generations hatch each year, depending on the species. Recently introduced from Asia, the brown marmorated stink bug (Halyomorpha halys), in addition to feeding on various plant parts, is also a nuisance pest that invades homes during the fall.
The number and species of sucking bugs present in fruit trees at any given time during the season are greatly dependent on the weather, the surrounding vegetation (alternate host plants), the orchard history, and other factors. Bugs normally are most abundant from bud break until about 6 weeks after bloom.
To sample plant bug and stink bug populations, shake trees over a ground sheet or beating tray. Begin sampling no later than pink bud, concentrating on trees or sections of orchards bordering woodlands, fencerows, or other favorable hibernation sites. White or yellow sticky-board traps also have been used to sample sucking bug populations. Preventing serious catfacing injury depends largely on well-timed, early season, broad-spectrum insecticide applications. Applications at petal fall, shuck fall, and 10 days after petal or shuck fall typically provide good control. Sprays during pink bud sometimes are applied when tarnished plant bugs are a major problem. Surround (kaolin clay) applications before and after bloom should provide partial reduction of plant bug and stink bug injuries.
Cultural practices can provide some suppression of sucking bugs. Destroying broadleaved winter annual weeds and legumes in and around orchards is an excellent practice. Legumes such as clover and vetch should be avoided as cover crops. Destroying early blooming broadleaved weeds before fruit tree bloom lowers the number of early catfacing insects. However, disturbing weeds during bloom or shortly thereafter might drive the bugs into the trees, causing more damage.