By Donald R. Lewis,
Iowa State University Extension
Trees often turn brown ahead of schedule, in mid- to late-summer, and for a variety of reasons. Trees may turn brown because of the weather (too wet or too dry), the planting site (too much clay, too much compaction of the soil or too little root space), the age of the tree (old and over-mature or just recently planted) or mechanical injury (assault on the trunk or roots).
Occasionally the problem may be related to a disease, but not often, and sometimes there may be insects. This is one of those years when insects are more important to trees than usual. We are completing a summer of greater-than-normal numbers of lace bugs on trees.
First, about the confusing name. There are two entirely different insects with the word "lace" in their names: lace bugs and lacewings. Both have lines within the wings (veins) that resemble lace (the familiar, open-woven fabric used for doilies and curtains). Lace bugs are plant pests that feed on sap from the leaves of trees and other plants. Lacewings are beneficial predators that eat aphids and other insects off the plants in the garden, field or landscape. Keeping these two insects apart in spite of their similar names is important to appreciating their divergent functions in the ecosystem.
Lace bugs are commonly found on the leaves of hackberry, sycamore and oak trees. Their numbers and the damage they cause vary greatly from year to year, presumably in response to variations in natural controls and the weather. For whatever reason, we have seen more lace bugs and more damage on more trees than usual this year.
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.
Lace bugs grow and develop on leaves 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 by piercing the leaf with their sharp beak. This causes a characteristic pale yellow or “bleached” spot on the upper leaf surface. After thousands to millions of punctures during the course of the summer, entire leaves and even the entire tree may turn brown.
Lace bug feeding damage usually looks worse than it is. Well-established, otherwise healthy trees appear to not be significantly affected by what amounts to an early fall. That's why insecticide treatments are usually not warranted especially in late summer after the tree has had nearly the entire growing season to grow and produce and store the products of photosynthesis.
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.
Earlier in the summer we could have applied an insecticide and expected some benefit to the tree. Spraying now is a waste of time, money and insecticide. The best thing for your brown tree is make sure it doesn't endure further stress. Water if the weather turns dry and try not to assault the tree trunk with the car bumper!