Although a tiny and attractive insect, the phlox bug nonetheless wreaks havoc on both wild and cultivated phlox, a plant prized for its showy flowers. Phlox bugs suck the sap from the leaves, stems, seeds and flowers of the phlox plant, causing leaves to die back and even killing the plant. Although prevention reduces the risk of harm from the phlox bug, pesticide treatments are sometimes needed to eliminate it.
Although phlox bugs are tiny--only about .2 inches in length, according to the University of Arkansas Cooperative Extension Service--they are distinct in appearance, usually boldly patterned with red and black coloration. Like the adults, the larvae are also orange or bright red, emerging from white eggs laid where the leaf attaches to the stem.
Phlox bugs attack primarily wild phlox plants, although they may also migrate to cultivated species. The bug inserts its mouth parts into the plant and drains the plant of water, and depletes its nutrients. First, the leaves show discoloration, then brown or yellow spots. Eventually, the entire leaf withers and drops to the ground. Over time, phlox bugs can destroy the entire plant.
Phlox bugs lay their eggs in the fall, which overwinter in dead phlox stems. In the spring, the eggs hatch in two generations, the first appearing in May and June and the second arriving in July and remaining until September, when the adults lay their eggs and die off for the year.
In the United States, the phlox bug's range extends from Maryland and West Virginia in the east to South Dakota, Minnesota, Mississippi and Arkansas. Phlox bugs range as far north as Canada. The University of Guelph Pest Diagnostic Clinic reports them as particular pests in Ontario.
Because phlox bug eggs overwinter in dead plant stems, gardeners should clean up and dispose of dead plant material, incorporating it into hot compost or discarding it completely. Phlox bugs may also take up residence in nearby weeds, so keeping weeds under control helps prevent infestation. The University of Guelph Pest Diagnostic Clinic warns, however, that disturbing weeds while in the blossoming stage may cause the bugs to migrate to new plants. If chemical controls are required, the Missouri Botanical Garden recommends pyrethrins, permethrin or acephate/orthene. The larvae are also susceptible to insecticidal soaps.