Lace bugs on Minnesota trees and shrubs
All lace bugs (family Tingidae) are plant feeders, attacking many types of plants; however, they are most commonly encountered feeding on the foliage of deciduous trees and shrubs. Their primary host plants in Minnesota landscapes include hackberry, walnut, basswood, white oak, bur oak, willow, chokecherry, hawthorn, cotoneaster and amelanchier (juneberry/serviceberry).
Lace bugs are 1/8 inch to 1/3 inch long (3mm – 8mm) and have light colored bodies with dark colored markings. The top of their wings, head, and thorax are composed of many raised ridges. These ridges give the insect a sculptured, lacelike appearance (Figure 1). On adults, the wings extend beyond the abdomen and are held flat. Nymphs are wingless and spiny with a flat oval shaped body. They are darker than the adults (Figure 2).
When lace bug nymphs molt their exoskeletons, these cast skins remain attached to the foliage of the plant (Figure 2). Adults and nymphs also leave dark, varnish-like excrement on the undersides of leaves (Figure 3).
Jeff Hahn, University of Minnesota
Figure 3. Lace bugs with their excrement attached to the bottom side of the leaf.
Lace bugs overwinter as adults on or near their host plants. They can be found in bark crevices and under leaves and other debris on the ground adjacent to these plants. In the spring, adults fly to plants and feed on newly-expanding leaves. The adults mate and lay tiny black eggs in small groups on the underside of the leaves. Eggs hatch into nymphs after about two weeks. Nymphs feed for approximately three to four weeks before maturing into winged adults that lay additional eggs. This second generation feeds until late summer or fall. Lace bugs typically have two generations per growing season in Minnesota. Adults from the second generation overwinter and begin the cycle anew the following spring.
Adults and nymphs feed on the undersides of leaves. They insert needle-like mouthparts into leaf tissue which creates small white or yellow spots on the leaf surface (Figures 4 & 5). Where populations are high, heavy feeding can cause severe leaf discoloration and premature leaf drop. Feeding damage is most noticeable in mid to late summer when populations are at their highest.
While feeding injury can discolor leaves, it does not normally threaten the health of woody plants. Healthy, mature trees and shrubs can tolerate damage from high populations of lace bugs. Heavy feeding occurring over several consecutive years on recently transplanted or stressed trees can reduce plant growth.
Lace bug populations vary from year to year. One year of severe damage does not necessarily mean that heavy damage will occur the following year.
Monitor susceptible trees and shrubs starting in late spring or early summer to determine if lace bugs are present. Pay close attention to plants that have had a history of infestation.
Plant health is normally not affected by lace bugs; the best option in most cases is to tolerate their feeding. Many natural enemies, such as assassin bugs, lady beetles, green lacewings, and other predators feed on lace bug eggs, nymphs and adults. When natural enemies are present, lace bugs generally cause little lasting damage.
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 lack wings, they cannot easily return to plants and are less likely to survive. Water sprays should be targeted at the undersides of the leaves where lace bugs are feeding.
Insecticides can be effective in reducing lace bug numbers. When using insecticides, good coverage is critical. Be sure to spray the undersides of the leaves where lace bugs are found.
Insecticidal soaps and horticultural oils are less toxic products that are effective against lace bugs and have low impact on natural enemies. These products do not have any residual and therefore need to come into direct contact with lace bugs to be effective. Repeat applications of these products may be necessary to achieve adequate control.
There are a variety of residual, broad-spectrum insecticides that are effective, such as permethrin, bifenthrin, lambda cyhalothrin and other pyrethroids (typically ending in –thrin), acephate, and carbaryl. Use these insecticides wisely and carefully, as they will kill natural enemies as well as lace bugs.
Important: Systemic insecticides, such as imidacloprid and dinotefuran, should not be used to treat lace bugs on flowering trees and shrubs as they are toxic to bees. Once applied, these insecticides can move into the pollen and nectar of flowers where they can contact bees.
If it is preferable to have a professional treat lace bugs on trees or shrubs, contact a licensed landscape pesticide applicator.
CAUTION: Read all label directions very carefully before purchasing and again before using an insecticide. Information on the label should be used as the final authority.