Adult azalea lace bug, Stephanitis pyrioides (Scott), and excrement. Photograph by James. L. Castner, University of Florida.

Lace bugs live on the underside of leaves and damage their hosts by piercing leaves with their straw-like mouthparts and removing the plant’s sap. Infested leaves have tiny yellow spots on the top surface and are discolored with dark, varnish-like excrement and old insect parts on the underside. Azalea plants begin to look unhealthy as insect numbers increase through spring and summer.

If you have azaleas, eventually you’ll have azalea lace bugs. But with a little knowledge, you can easily control these insects that discolor the leaves of azaleas.

Azalea lace bugs spend winter as eggs on the underside of azalea leaves. They hatch in early to mid-March and then begin to feed and develop into adults.

Lace bugs complete their first generation by late April. Then they increase in number throughout the remainder of spring, summer and fall. These insects can complete three to five generations in a single growing season. In late September adult lace bugs of the final generation for the season lay eggs that carry the population through winter.

The key to easily controlling azalea lace bugs is to properly time the control efforts.

Inspect plants in early spring to see if the insects are present. Look for leaves that are whitish to yellow on the top surface (leaves may be mottled in appearance) and that have small, dark, varnish-like spots on the undersides. If leaf damage is heavy, continue to check the plants every week for small lace bugs. You should begin to see them in late March through April.

Early to mid-spring is the best time to control the first generation of the bugs. Proper timing of the insecticide application will reduce the need for further sprays during the rest of the growing season.

Horticultural oil or insecticidal soap can provide acceptable control. Do not use a dormant oil spray on evergreen-type plants. Dormant oils are designed to be used on dormant plants while they are bare of leaves and during cool temperatures. Dormant oil products can damage evergreen plants, especially during the warmer temperatures of spring and summer. Look for a horticultural oil that is designed to be used on evergreen plants during warmer weather with key words such as “year round,” “all seasons” and “ultra-fine.” Or use one of the insecticidal soap products.

Make sure to spray the backs of the leaves. And only spray early in the morning or late in the evening when it’s cooler but never during the heat of the day or when the plant is in full sun. Follow instructions on the pesticide label concerning mixing, application and safety precautions. Larry Williams, UF/IFAS Extension Agent, Okaloosa County

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