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Plant Bugs on Perennials and Landscape Shrubs

(fourlined, tarnished and phlox plant bugs)


Classic fourlined plant bug feeding damage on leaf.

Fourlined plant bug nymphs are first entirely red in color, but they obtain black wing pads as they get into later instars.

Species:

The fourlined plant bug, Poecilocapsus lineatus, is the most common plant bug pest encountered in perennials and landscape shrubs. The tarnished plant bug, Lygus lineolaris, is another generalist plant feeder common in landscapes. Other plant bugs usually have very narrow host plant ranges, such as the phlox plant bug, Lopidea davisi, yucca plant bug, Halticotoma valida, and hollyhock plant bug, Brooksetta althaeae.

Distribution:

The fourlined plant bug is found east of the Rocky Mountains, and tarnished plant bugs inhabit all of North America. The other species are usually found wherever their hosts are cultivated.

Hosts:

Fourlined plant bugs have been found on over 250 species of plants in 57 families; tarnished plant bugs have been found on over 380 hosts! Most of the other species prefer single host plants or restrict their feed to a single genus or family of plants. In typical urban landscapes, the fourlined plant bug damage is most commonly found on perennials (especially those in the mint family or composites), but they commonly attack shrubs including: azalea, dogwood, forsythia, viburnum and weigelia. The tarnished plant bug seems to prefer plants in the aster and rose families.

Damage:

Most plant bugs appear to insert their mouth stylets into host plant tissues and inject a tissue dissolving saliva. They then suck out the liquified plant tissues. This produces a typical sunken lesion which can be circular or angular, depending on the host plant leaf structure. Feeding on immature leaves can cause considerable leaf distortion - cupping, twisting and crumpling. Occasionally, the lesion spots dry and fall out, producing small holes in leaves.

Description and Life Cycle:

Plant bugs have the characteristic “bug” shape - elongate oval bodies with a diamond-shaped zone on the posterior where the wing membranes cross, and a pentagonal-shaped pronotum (the area just behind the head). All have long antennae and long legs. They run and often fly when disturbed.

The fourlined plant bug is yellow-green with four longitudinal black stripes down the back. However, the nymphs are a bright crimson red with black wing pads. The tarnished plant bug adult is a mottled tan and brown and the nymphs are usually greenish. The phlox plant bug is a reddish-orange color as is the yucca plant bug. The hollyhock plant bugs are green.

Most plant bugs appear to spend the fall and winter as eggs inserted into host plant tissues, but the tarnished plant bugs overwinter as adults hiding in leaf litter. The fourlined plant bug has one generation per year with nymphs hatching in April to early May, and new adults appearing by late May and early June. The other plant bug species usually have 2 to 4 generations per season. Damage is most severe when the nymphs are feeding on developing plant tissues in the spring.

Fourlined plant bug adults are yellow with four black stripes.

Tarnished plant bug adults are mottled brown in color.

Tarnished plant bug nymphs produce damage similar to fourlined plant bugs. The nymphs are green with brown wing pads.

Control Hints:

Most plant bugs are considered aesthetic nuisance pests since they rarely kill their host plants. However, leaf and flower distortion can be very severe and can greatly reduce the aesthetic value of landscape plants.

Option 1: Cultural Control - Destroy Overwintering Eggs & Habitat - Since the eggs of most plant bugs are inserted into host plant tissues by the fall, cutting and removal of dead plant stalks of perennials can reduce plant bug innoculum for the next season. Be sure to bury or compost removed plant material or remove residues from the landscape area. Remove leaf litter and reduce mulch thicknesses to eliminate areas where tarnished plant bug adults can overwinter.

Option 2: Cultural Control - Hand Crush Nymphs or Syringe - In low populations, the small plant bug nymphs can be located within host plant leaves and crushed. Be careful to cup you hands around affected leaves since the nymphs will quickly run or drop from the plant. A hard spray of water, syringing, can often knock plant bug nymphs from their host plants and these nymphs often have difficulty reestablishing on their hosts.

Option 3: Chemical Control - Soaps & Oil Sprays - Plant bug nymphs are very easily destroyed by insecticidal soap or horticultural oil sprays, but the nymphs have to be contacted with the emulsions. Be careful when using soaps or oils on perennials that have set flower buds or are flowering as phytotoxicity can occur.

Option 4: Chemical Control - Standard Insecticides - Both contact and systemic insecticides are effective for control of plant bugs. Applications of contact insecticides, e.g. pyrethroids, should be made as soon as the first sign of nymphal bug feeding is noticed. Since many soil applied systemics require several days to weeks to be absorbed, apply these several weeks before plant bug nymphs are expected. This will help reduce plant distortion.