Lace bugs are sap feeding insects commonly found on the leaves of shade trees in Iowa. Trees most commonly affected are hackberry, sycamore and oak. Lace bug growth and development occurs throughout the summer though it is typical to notice the damage and the adults in late August and September.
Lace bugs feed on the underside of the leaves. They pierce the leaf epidermis with their sucking mouthparts and cause the characteristic pale yellow, scorched or “bleached” discoloration on the upper leaf surfaces. The underside of heavily infested leaves will be speckled with small, black, shiny "varnish spots" (excrement).
Lace bug adults have attractive wings that are beautifully sculptured with an intricate pattern of veins resembling lace. The wings and thorax are flat on top and appear white. The wings extend out over the sides of the black body. Adults are approximately 3/8-inch long. The nymphs are black, spiny and pointed at both ends. Clusters of empty nymphal "shells" (exoskeletons) are usually present on the leaf undersides.
Lace bug damage varies greatly from year to year, presumably in response to variations in natural controls and the weather. Severe feeding may cause premature leaf drop, but otherwise healthy trees appear to be unaffected.
Severe damage is usually not noticed until mid to late summer. Treating in late summer, after the damage is apparent is of little or no benefit to the infested tree. Most damage is done by the nymphs in mid-summer. Spraying will not return green color to the already-damaged leaves. Further, spraying when it is too late for effective control may cause more harm than good by killing the pests’ natural enemies such as predators and parasites.
Though treatment does not help the tree, there may be adequate nuisance created by lace bugs dropping from infested trees to warrant control attempts. Though the lace bugs are harmless to people, pets, structures, and landscape plants there may be a desire to treat to alleviate the annoyance. Insecticides to prevent lace bug injury or to alleviate lace bug annoyance include insecticidal soap, and other insecticides labeled for this pest. Read and follow label directions. For more information on insecticides please see this article.