Azaleas are among the most commonly grown flowering shrubs in home gardens. Usually easy to grow, they are sometimes afflicted with the azalea lace bug. If you find that your evergreen azaleas have bleached or yellowing leaves, they may have azalea lace bug. Fortunately, this problem is easy to diagnose and treat.
Resembling a small housefly, azalea lace bug (Stephanitis pyrioides) is about 3 mm long with curving, lacy wings. It lays it eggs on the back of evergreen azaleas and some other evergreen species. After hatching, the nymphs (larvae) suck nutrition from the leaves, causing yellowing (chlorosis). The entire life cycle takes about 45 days in early spring, accelerating to 22 days as the weather warms. Several generations occur during one season.
Azaleas affected by lace bug lose their bright green color and become yellow or bleached-out green. White and green spotting sometimes appear. Adult lace bugs are not often seen, but a careful inspection of the back of leaves sometimes reveals eggs along the veins, or feeding nymphs. More often seen is the black, spotty excrement left by nymphs. Severely affected plants can die.
Healthy azaleas given proper conditions including plenty of room to prevent crowding, are less likely to become severely affected by azalea lace bug. Pay attention to watering and fertilization. Plants in the shade are less likely to be severely affected than those in the sun.
Azalea lace bug is easily treated with most insecticides. Systemic sprays are very effective. The chemical penetrates the leaves and enters the sap, which the nymphs suck. Insecticidal soaps are often effective, but will have to be applied more often. Use all products according to label instructions. Treatment will not restore the appearance of affected leaves, but new growth will be fresh and green.
Lady bird beetles (ladybugs) are natural predators of lace bug and can be purchased from garden centers. Other predators include assassin bugs, lacewings, jumping spiders, pirate bugs and predatory mites. Unfortunately, these insects are not often present in sufficient numbers until lace bugs have done damage, so some spraying may be necessary. Use horticultural oil or insecticidal soap, which are less toxic to beneficial insects.