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Lace bugs: Damage not seriously harmful

February 23, 2002|By Eric Natwick, University of California, Imperial County Cooperative Extension adviser

Lace bugs are common insects and several species feed on landscape plants in California, but each species feeds on only one or a few closely related plants, including alder, ash, birch, chrysanthemum, fruit trees, sycamore, toyon, walnut and willow.

Lace bugs are sapsuckers that usually live on the undersides of leaves. They cause damage to plants by stippling and bleaching leaves. Lace bug damage can be distinguished from mite feeding by the presence of cast skins and dark specks of excrement deposits on the lower leaf surface.

Certain other plant bugs and thrips also produce both leaf stippling and dark excrement, and mites commonly stipple the leaves, so examine the lower leaf surface for insects to distinguish these pests.

Nymphs produce honeydew, which drops to the foliage below and becomes blackened by sooty mold fungi. The bugs usually appear during the summer.


Corythucha is the most common genus of the lace bugs. The lacelike thorax and forewings conceal the one-eighth-inch long, flat body of adult lace bugs. Nymphs are wingless, smaller, oval and spiny. All stages congregate in groups on the undersides of leaves. Adult female lace bugs insert tiny eggs in plant tissue, often hidden under excrement. Nymphs hatch from eggs and molt five times over about six weeks before appearing as adults. There can be several generations per year.

Tolerate lace bug damage if it is not unsightly, as it usually does not seriously harm plants. Manage plants with proper watering and fertilizer to maintain vigorous growth and as plants grow they often will outgrow the lace bugs. Prune stippled leaves as they are replaced by new growth.

Several common predators attach lace bugs including: lacewings, assassin bugs, spiders and predaceous mites. Predator populations usually do not become abundant until after lace bugs become abundant. However, preservation of natural enemies is an essential part of a long-term integrated lace bug management program. Grow plants well-adapted to our desert conditions. Often lace bugs are more severe on plants in hot, sunny locations.

Several insecticides are effective for control of lace bugs. Azadirachtin (Safer, BioNeem), an extract from the neem tree, can be used by home gardeners for bug control. Insecticidal soaps (Safer), narrow-range oil (Green Light, Volck), or neem oil (Green Light Rose Defense) if applied properly can temporarily lower lace bug abundance.

To be effective these products require thorough coverage on the undersides of leaves. Imidacloprid (Bayer Advanced Tree and Shrub Insect Control) is available to homeowners and is an effective soil applied systemic insecticide that can provide lace bug control. These insecticides are safe for humans and pets and less likely to adversely impact natural enemies than more persistent, broad-spectrum insecticides.

The foliar insecticides listed above do not have long residual activity and lace bug eggs are protected within plant tissue. Application may need to be repeated to maintain control. Thoroughly spray leaf undersides when lace bug nymphs first appear on foliage in spring and repeat several times at intervals of about two weeks to maintain good control. Imidacloprid is used as a soil drench into the soil beneath the plant and may provide season-long control but must be applied early in the season before populations dramatically increase.

More persistent, broad-spectrum insecticides — acephate (Orthene) a systemic insecticide that moves within the plant, carbaryl (Sevin), Malathion, and cyfluthrin (Lawn and Garden Multi-Insect Killer) — may be applied for lace bug control. With the exception of the soil-applied imidacloprid, broad-spectrum insecticides provide longer-lasting control than do azadirachtin, soaps and oils. However, broad-spectrum insecticides kill many natural enemies of lace bugs.

As a result, secondary pest outbreaks, such as spider mites, may follow sprays of broad-spectrum persistent insecticides. Read and follow all label directions before using any pesticide.

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