21 April 2008
Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580 fax: 434.872.4578
There are a variety of lace bugs in our environment and they feed on many of our ornamental trees and shrubs including azalea, rhododendron, sycamore, broad-leaved evergreens, and others. In the spring we may notice symptoms and signs from these insects from last year and this is a good opportunity to plan for the coming season.
Lace bug damage is usually first noticed as yellow spots on the upper leaf surfaces of affected plants. Lace bugs actually feed on the undersides of leaves with their piercing-sucking mouthparts, but because they kill surrounding cells as they feed, they cause yellow spots to appear on upper sides of the leaves. The first yellow spots that appear are very similar to mite damage, but the spots made by lace bugs are larger. When feeding damage becomes severe, the leaves take on a gray blotched appearance or can turn completely brown. As lace bugs feed they produce brown varnish-like droppings that spot the underside of the leaves. These droppings further distinguish lace bug damage from mite damage. When large numbers of lace bugs are present cast skins can often be found attached to the leaves where they molt.
Adult lace bugs are about 3 to 6 mm (1/8"- 1/4") long with a netlike pattern on the wings. In addition, the wings are dotted with brown and black. The immature stages, called nymphs, are similar except they are smaller and often have spines. The eggs, although small, are easily distinguished by their elongate and cylindrical shape. They resemble small black smokestacks attached to the undersides of the leaf. Lace bugs are classified in a group we call true bugs and they are closely related to some of our other insect friends such as the stink bugs, squash bugs, and assassin bugs.
On deciduous plants, adult lace bugs overwinter in protective places on the host, such as bark crevices and branch crotches, or on the ground in leaf litter. They end their hibernation just as spring growth starts. They attach their eggs to the undersides of the leaves often along the midribs, sometimes covering them with a black varnish-like coating. The eggs will stay attached to the leaves long after they have hatched and can be recognized by noting if the tops have openings. The nymphs complete their life cycles quickly and one to several generations can occur in one season; usually, there are two generations. Some lace bugs can complete a generation in as few as 30 days. Usually, by the end of the summer, all life stages can be found on a host.
On broad-leaved evergreens, lace bugs overwinter as eggs on the undersides of leaves. Eggs hatch in May in Virginia and two or more generations may occur during the growing season.
The azalea lace bug, Stephantis pyrioides (Scott), completes two generations in Virginia per year. The second brood builds up to high populations in August and September and damage can be severe. In some cases, the leaves turn completely brown and are heavily spotted with droppings by the end of the summer.
The hawthorn lace bug, Corythucha cydoniae (Fitch), selectively attacks a variety of woody, rosaceous plants and can cause severe leaf damage. It has been reported on apple, button bush, cotoneaster, hawthorn, serviceberry, loquat, oak, pear, pyracantha, and quince.
Lace bug control requires careful monitoring early in the season. The presence of beneficial insects may mean that chemical use can be avoided. If chemicals are used treatments should be applied where insects are found on the foliage, either on adults on deciduous plants or on groups of nymphs on broadleaf evergreens. It is very important to spray the undersides of the leaves because this is where they feed. Control of the first generations is most important to slow population buildup. Current control recommendations include the following chemicals. Acephate (Orthene), carbaryl (Sevin), cyfluthrin, imidacloprid (Merit), malathion, methoxychlor, pyrethrins + PBO, and tetramethrin. Consult the label for host plants and specific pests listed under directions for use and please use pesticides safely.
The common pattern we see is lace bug outbreaks on azaleas growing in landscapes that are structurally simple. Structural complexity is a measure of the amount of vegetation at the various plant strata (such as overstory, understory, shrub, etc.). The more plant material within a landscape the less likely lace bugs will cause trouble.
It was originally believed that lace bug outbreaks were related to sun and shade. The theory being that azaleas (which are truly understory shrubs) grown in the sun were stressed and therefore better food for lace bugs. Studies found that this was not the case and that lace bugs performed better on foliage from shade grown azaleas. Other studies found that natural enemies were the driving force in these outbreak patterns. Structurally complex landscapes support a greater abundance and diversity of natural enemies than structurally simple landscapes. One of these natural enemies is the green lacewing. Green lacewings are native and common but can be purchased to augment a situation where lace bugs are a problem.
For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.