This is the time of the season when the characteristic chlorotic leaf spot damage (= stippling) from Lace Bugs (order Hemiptera; family Tingidae) that feed on deciduous woody ornamentals as well as a few herbaceous perennials becomes very evident. These small plant-sucking insects are so named because of the lace-like pattern of the veins and membranes in their wings which are held flat over their body.
Most lace bug species found in Ohio live on the lower leaf surface of their host plants. Flipping leaves over at this time of the year may reveal all the incomplete metamorphic life stages. Adults are tiny measuring no more than 3/16” long. The immatures (nymphs) are even tinier and appear to be covered in small spikes.
Both the adults and nymphs exude black tar-like fecal deposits. This tell-tale feature of lace bug activity adds to the unsightly appearance of heavily infested leaves.
The oval or flask-shaped eggs of most species are black which may cause them to be confused with fecal spots. However, the fecal spots are randomly distributed while the eggs are grouped in loose clusters.
Research has shown that adults of some species actively guard their eggs and nymphs against predation. This may explain why it is common to see adult females remaining close to egg clutches. It is also common to see adult females apparently “herding” groups of nymphs.
Damage and Symptom Development
Adults and nymphs use their piercing-sucking mouthparts to suck juices from the leaves. If the feeding is done on the lower leaf surface, the damage appears on the upper leaf surface as tiny chlorotic stippling. The opposite occurs with those species that live on the lower leaf surface. High winds and heavy rains can drive lace bugs to lower leaves, so the stippling damage may be heaviest in the lower canopy.
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. I first noticed this odd symptom with basswood lace bugs on silver linden owing to the dark green upper leaf surface. However, it can also be seen with other lace bugs.
Eventually, the stippling will coalesce to produce large white patches causing leaves to look "bleached-out." As the damage progresses, 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. Many lace bugs in Ohio have 2 to 3 generations per season with the leaf damage ramping up with each successive generation. This means it's critical to manage lace bugs right now to halt further damage over the rest of the growing season.
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 the experience of sipping an Old Fashioned in the shade of an infested oak tree.
A Rogues Gallery of Lace Bugs
Heavy oak lace bug (Corythucha arcuata) damage recently drew my attention to oaks (Quercus spp.) in a commercial landscape with leaves becoming yellowish-white. However, the leaves were also being stippled by Oak spider mites (Oligonychus bicolor); a reminder that plants may have more than one pest causing damage at the same time.
Oak spider mites are unusual compared to many other spider mites in that they feed on the upper leaf surface. They also tend to concentrate their stippling around leaf veins. As with all spider mites, they use their fag-like chelicerae to rupture individual leaf cells so they can ingest the contents. Thus, spider mite stippling is much smaller compared to lace bug stippling.
It's also important to separate symptoms produced by lace bugs from those produced by foliar diseases such as powdery mildew. Management for one will not affect the other.
Other lace bugs that are beginning to produce noticeable damage in Ohio include basswood lace bug (Gargaphia tiliae); buckeye lace bug (C. aesculi); chrysanthemum lace bugs (C. marmorata); sycamore lace bug (C. incurvata); and walnut lace bug (C. juglandis).
The buckeye, oak, and walnut lace bugs confine their feeding to their namesake hosts. Sycamore lace bugs may be found on American sycamore (Platanus occidentalis) and to a lesser extent on London planetree (Platanus x acerifolia).
Basswood lace bug grew up with American basswood (Tilia americana); however, it commonly focuses its attention on silver linden (T. tomentosa). This tough European native can handle many of the urban slings and arrows that send less hardy trees to wood chippers. However, our native lace bug may turn silver lindens into golden-brown lindens by August in the Greater Cincinnati region.
Despite its common name, the hawthorn lace bug (C. cydoniae) has one of the most cosmopolitan palates of any lace bug found in Ohio. It will feast on a wide variety of rosaceous plants as well as a few plants outside of the rose family such as common buttonbush (Cephalanthus occidentalis). However, they are most commonly found on hawthorn (Crataegus spp.), serviceberry (Amelanchier spp.), Cotoneaster spp., firethorn, (Pyracantha coccinea), and occasionally rose (Rosa spp.).
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, Rudbeckia, goldenrods, and sunflowers. These lace bugs may occur in greenhouses as well as landscapes. Indeed, landscape infestations may originate in greenhouses.
Suppression includes simply applying a heavy jet of water to blast away the lace bugs. Of course, adults have wings, so the adults may thwart the "water park ride" approach to management by simply flying back to the leaves.
Insecticidal soaps and horticultural oils are effective and have a higher safety margin for non-target insects such as beneficials (e.g. pollinators, predators, parasitoids, etc.). However, direct contact is required. So, make sure to target the undersides of leaves.
Traditional topically applied insecticides present several challenges. First, most of the insecticides that are sprayed onto plant surfaces work best as stomach poisons which present a mode of entry issue with plant-sucking insects. Lace bugs are sucking insects meaning they won’t ingest the insecticide. So, insecticide efficacy is almost entirely based on direct contact just like soaps and oils. Second, topically applied insecticides are indiscriminate insect killers. They may kill non-target insects such as predators and parasitoids that help to regulate pest populations.
Systemic insecticides solve the mode of entry issue with plant-sucking insects and also present a lower risk to non-target insects as long as they are applied as soil drenches/injections or bark sprays (e.g. dinotefuran) rather than foliar sprays. Systemic insecticides effective against lace bugs include flupyradifurone (e.g. Altus), and acephate (e.g. Orthene, Lepitect), as well as neonicotinoids such as dinotefuran (e.g. Safari, Transtect) and imidacloprid (e.g. Merit, Xytect).
Of course, as with using any insecticide, you must read and follow label directions paying close attention to applicator and environmental safety recommendations as well as application mix ratios and timing. For example, 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 this season.