Q: Iβve been noticing the sycamore trees around where I live look pretty awful. The leaves are pale and curled up. What is causing this problem?
A:Β The local trees in Tucson are being eaten by the sycamore lace bug (Corythucha ciliata), a native insect, and present across North America. Sycamore lace bugs cause damage to leaves on sycamores as well as London plane trees. These lace bugs are white in color, about 1/8 inch in size, and feed on the underside of leaves on host trees. Adult lace bugs tend to have an almost see-through appearance, which, combined with venation on wings and ridges on their bodies, lends them their common name. The nymphs differ in appearance from the adults in that they are black and spiny. Adults are very mobile and their movement is aided by wind. Lace bugs go through five life stages: egg, three immature or nymph stages, and adult. Adults overwinter in bark crevices or branch junctures, and become active again in the spring when leaves begin to break from their buds. Shortly thereafter, the adults lay eggs on the underside of leaves and eggs hatch within a matter of days of being laid. Nymphs feed on the underside of the leaves as they grow. Nymphs, which are wingless, smaller, and more rounded in shape, tend to cluster together on the underside of infested leaves. Wherever they are feeding, frass (insect feces) may be seen as well. The frass appears as tiny drops, shiny and dark in color. The life cycle is about 45 days in length, allowing for several generations throughout the year.
Early infestations are evident when white spotting begins to occur on leaves where the insects are feeding. Black spots, the frass of the insects, appear widely across the underside of the leaves as well. Heavy infestations can result in bronzing and drying of leaves. Eventually, those leaves will fall prematurely, making trees look to be in poor health. Established trees can sustain this damage for several seasons. Young or newly planted trees experience more adverse effects during infestations than established trees. The damage is more severe as weather patterns bring drier conditions.
Though there are insecticides and other types of management actions that can be taken, most damage is aesthetic. Watering trees properly can help relieve stress on trees. Additionally, strong streams of water on leaves can be effective in removing insects, especially when targeting lace bugs in the nymph stage, before severe damage occurs. However, these infestations do not require any treatment. There are also natural fungi as well as predators and parasites of lace bugs that can help manage populations.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to plwarren@cals.arizona.edu.
