Lawn Disease Prevention

Lace bugs are common pests of azalea, rhododendron, sycamore, broad-leaved evergreens, and many deciduous trees and shrubs. They often go undetected until the infested plants show severe damage. 

Adult lace bugs have highly ornamented wings and a hood-like structure covering the head. The entire surface of the insect is covered with veins that look like lace. Adult lace bugs are about 1/8- to 1/4-inch long with a netlike pattern on the wings, which are dotted with brown and black. The immature stages (nymphs) are similar except they are smaller and often have spines. The eggs resemble small, black smoke stacks attached to the undersides of the leaf.

Biology and Habits

The biology and habits of lace bugs vary somewhat according to species. Lace bugs can be divided into two groups: those that attack deciduous trees and shrubs and those that attack evergreen shrubs. Lace bugs that attack deciduous plants spend the winter in the adult stage by hibernating on the plant under bark or near the plant in leaf litter. Lace bugs that attack evergreens overwinter in the egg stage attached to the leaves.

The hawthorn lace bug is one species that attacks deciduous plants. The adults hibernate under loose bark of their host plants as well as among leaf litter. They become  active in early to mid-May and return to the new leaves. Only one generation occurs per year. Related species of lace bugs, such as the oak, sycamore, and hackberry lace bugs, have two and occasionally three generations in a summer.

The azalea lace bug is an example of a lace bug that attacks evergreens. The nymphs hatch in the spring, usually mid-May. They feed in small groups on the under surface of leaves. The adults mate and lay eggs for a second generation by mid to late-July. Often there is a third generation in the late summer and early fall.

Damage

Lace bugs cause feeding damage that is readily distinguished from that of other  insects and mites. Although lace bugs feed on the underside of leaves, the damage is most apparent on the upper leaf surface; they kill surrounding cells as they feed, causing large yellow spots to appear on the upper sides of the leaves. Positive identification of lace bug damage can then be confirmed by the presence of brown to black droplets of excrement and old "skins" of the nymphs on the underside of damaged leaves.

Control

Plants that attract lace bugs should be monitored early in order to determine if an infestation is building.  Elimination of the first generation of lace bugs is necessary if visual damage is to be avoided. Existing spotting and yellowing of leaves will not disappear once the lace bugs have been controlled.

Cultural: Most lace bug problems occur in bright, sunny areas; plant susceptible plants in shade. The azalea and rhododendron lace bugs are rarely a problem when their host plants are in a shaded understory. Another effective control method is to use a hard jet of water from a hose to dislodge the young nymphs as they hatch in the spring. 

Biological: Encourage natural predators of lace bugs. Green lacewings, mites, and assassin bugs all attack lace bugs and will generally keep a lace bug population in check, especially if host plants are sited properly. However, these predators often arrive after considerable damage has occurred. In order to conserve beneficial natural predators use a hose spray or insecticidal soaps or oils instead of standard insecticides.

Chemical: Insecticidal soaps and horticultural oils are useful if they contact the nymphs directly. Be sure to cover the underside of the leaves where the nymphs are feeding. Additional applications may be needed to control nymphs hatching out of late-laid eggs or if reinfestations occur from surrounding landscapes. Several over-the-counter insecticides are effective in lacebug control, but soaps and oils are usually adequate. Be sure to check the product label as not all lace bugs or host plants are listed on each label. Make applications as soon as the eggs hatch in the spring, usually mid to late-May. Monitor the plants and repeat applications if reinfestations occur. If plants are repeatedly attacked, consider moving them into the shade.

Adapted from the Virginia Cooperative Extension and the Ohio State University Extension, 1999; University of Georgia Cooperative Extension Service