Lace bugs on deciduous trees and shrubs
Published in Yard & Garden Brief, October 2002
Lace bugs are pests of a wide variety of trees and shrubs in Minnesota. Their hosts include hackberry, walnut, basswood, white oak, bur oak, willow, chokecherry, hawthorn, amelanchier (serviceberry), cotoneasters, and other ornamentals. Lace bugs are 1/8 to 1/4 inch long, have light colored bodies, and elaborate, ornate, lacy wings that look broad and flat from above (Figure 1).
Lace bugs overwinter as adults on or near their host plant. In the spring, adults fly to newly-expanded leaves where they feed and lay black eggs in small groups. The eggs hatch into wingless young called nymphs. The nymphs are dark brown or black and are sometimes covered with long spines. They feed for approximately three weeks before maturing into the winged adults that lay eggs. Normally there are two generations of lace bugs per year in Minnesota.
Lace bugs feed on the undersides of leaves. They insert needle-like mouthparts into leaf tissue, which causes small white or yellow spots on the surface of the leaves. Heavy feeding can cause striking leaf discoloration and early leaf drop. Other signs of lace bugs are dark, varnish-like excrement and shed skins on the undersides of leaves (Figures 2 & 3). Lace bug feeding damage is most noticeable in mid to late summer as populations increase.
Lace bug feeding often reduces the aesthetic quality of plants. Lace bugs do not normally threaten the health of woody plants; healthy, mature trees and shrubs can tolerate high populations. However, lace bugs can damage trees and shrubs if heavy feeding occurs over several consecutive years, or if the plants have recently been transplanted or stressed.
An abundance of lace bugs one year does not necessarily mean that the next year's population will be high. Generally, lace bugs are not a problem year after year. If lace bugs are a perennial problem, or if you have plants that have been transplanted or stressed recently, begin monitoring efforts early and manage lace bugs before severe damage occurs.
Tolerate lace bugs when possible. Natural enemies, such as lady beetles, green lacewings, and other predators help keep lace bugs in check. When natural enemies are present, lace bugs generally cause little damage to the plant.
A high-pressure water spray from a garden hose is an option for managing lace bug nymphs on small plants. The water spray acts much like a heavy rain, knocking nymphs off the plant. Since nymphs can not fly back to the plant, they are less likely to survive. Direct the spray at the undersides of the leaves where most lace bugs are found.
Insecticides can be effective in reducing numbers of lace bugs on plants. Use insecticides judiciously, as they kill natural enemies as well as lace bugs, and can make lace bug problems worse. Avoid spraying broad-spectrum insecticides (i.e., acephate, carbaryl, and chlorpyrifos) when possible to preserve natural enemies for good long-term management.
When using insecticides, good coverage is critical. Be sure to spray the undersides of the leaves where lace bugs are normally found.
It is best to use the least toxic products first. Insecticidal soaps (e.g., Safer's), horticultural oils, and pyrethrins are insecticide products with relatively low toxicity, and are relatively safe for many beneficial insects including natural enemies. Other products to manage lace bugs are cyfluthrin, permethrin, carbaryl (e.g., Sevin), or acephate (e.g., Orthene).
CAUTION: Read all label directions very carefully before purchasing and again before using any insecticide. Information on the label should be used as the final authority.