Lace bugs do well in hot weather and they are certainly doing very well. I'm finding population densities and levels of damage that are normally seen in July. I posted a report on hawthorn lace bugs (Corythucha cydoniae) this past Saturday [see "Hawthorn Lace Bugs Affect More Than Hawthorns," June 16]. This report highlights a few others.
Most lace bug species found in Ohio live on the lower leaf surface. They are tiny insects with the adults measuring no more than 3/16" long. Lace bugs are so-named because of the lace-like pattern of veins and membranes in their wings. The nymphs are even tinier and appear to be covered in small spikes.
Both the adults and nymphs use their piercing-sucking mouthparts to suck juices from the leaves. Although feeding is done on the lower leaf surface, the damage appears on the upper leaf surface as tiny chlorotic spots (= stippling).
The first thing you may notice on infested trees are leaves with areas that look "bleached-out," or leaves that are entirely white to light brown. High winds and heavy rains can drive lace bugs to lower leaves, so the damage may be heaviest in the lower canopy. Look closely to make certain you're seeing stippling and not another plant problem such as powdery mildew.
The stippling may at first appear as distinct 1/4 - 1/2" diameter spots on the upper leaf surface created by 1st instar nymphs feeding near the cluster of eggs from which they hatched. Eventually, the stippling will coalesce to produce large white patches as the damage becomes more widespread. Another feature of lace bugs are black tar-like fecal deposits that add to the unsightly appearance of heavily infested leaves.
Heavily damaged portions of the leaf, or entire leaves, will turn yellow to copper-brown. High lace bug populations can produce enough leaf damage to cause early leaf drop, branch dieback, and even the death of small trees and shrubs.
Lace bugs can also be a serious nuisance pest. They have a penchant for dropping from heavily infested trees onto unsuspecting hikers, picnickers, and patrons of outdoor bars and cafes. They don't feed on people, but they can use their piercing-sucking mouthparts to deliver a pinprick bite particularly if they fall between a person's neck and shirt color. Adding insult to injury, floating lace bugs can ruin a good Mai Tai.
A Rogues Gallery of Lace Bugs
Aside from the aforementioned hawthorn lace bugs, other lace bugs producing noticeable leaf damage in Ohio include: basswood lace bug (Gargaphia tiliae), buckeye lace bug (C. aesculi); oak lace bug (Corythucha arcuata), sycamore lace bug (C. incurvata); and walnut lace bug (C. juglandis). I'm also getting reports of chrysanthemum lace bugs (C. marmorata) on the rise in the central part of the state.
The buckeye, oak, and walnut lace bugs confine their feeding to their namesake hosts. Sycamore lace bugs may be found on American sycamore and to a lesser extent on London planetree. Basswood lace bugs feeds on all members of the Tilia genus; however, they have are particularly fond of silver linden (T. tomentosa).
Chrysanthemum lace bugs (C. marmorata) are unusual in two ways. They are found on both the lower and upper leaf surfaces and they may feed on a wide range of herbaceous perennials in the Asteraceae family including asters, black-eyed Susans, goldenrods, and sunflowers. These lace bugs may occur in greenhouses as well as landscapes. Indeed, landscape infestations may originate in greenhouses.
The lace bugs in this report can have 2 to 3 generations per season in Ohio with leaf damage ramping up with each successive generation. This means it's critical to target the current first generation with control measures to halt further damage this season.
Suppression includes simply applying a heavy jet of water to blast away the lace bugs. Of course, adults have wings, so they can fly back to trees meaning more "water treatments" may be necessary. Insecticidal soaps and horticultural oils are effective; however, direct contact is required. So, make sure to target the undersides of leaves. The same is true for pyrethroid insecticides; they are stomach poisons but lace bugs are sucking insects.
Some systemic insecticides such as acephate (e.g. Orthene, Lepitect) and the neonicotinoids dinotefuran (e.g. Safari, Transtect) and imidacloprid (e.g. Merit, Xytect) are effective against lace bugs. However, imidacloprid must be applied with enough lead-time to allow the active ingredient to migrate to the leaves in a high enough concentration to kill the bugs; it may be too late.
Of course, before using any insecticide, you must read and follow label directions paying close attention to plant safety as well as avoiding impacts on pollinators. This includes making certain sprays do not drift or runoff onto non-target flowering plants.