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Description and Biology

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Adult female azalea bark scales, Eriococcus azaleae, are dark red with short legs and antennae and long, thread-like mouthparts. The insect is usually hidden from view by the egg sac or ovisac, a white covering of felted or matted waxy threads. The sac is about 1/8 inch long and 1/16 inch thick. Reddish purple eggs are laid within the egg sac, occupying the void left by the female's shrinking body. Eggs are laid in late April. They hatch about 3 weeks later in early May. This new generation matures during the summer and produces eggs that hatch in September. Newly hatched nymphs, called crawlers, are tiny and crawl out of the egg sac onto the bark where they settle especially near twig crotches. Crawlers soon penetrate the bark with long, thread-like mouthparts, begin to feed by sucking out sap. They then begin excreting honeydew. These nymphs are inconspicuous and practically free of any waxy covering. Mature females tend to feed in crotches and on twigs. Adult males have two wings and are tiny. Males tend to feed on leaves. Azalea bark scales overwinter as nymphs feeding through the bark.

Azalea bark scales

Azalea bark scales cover themselves with a felted white ovisac.

Azalea bark scale eggs

Azalea bark scale eggs are protected by the ovisac.

Host Plants

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Infested plants often become darkened with sooty molds, fungi that grow in the honeydew excreted by these sucking pests. Infested azaleas also become yellowish and unthrifty. The azalea bark scale has been reported from andromeda, four azalea species, blueberry,"flowering cherry," hawthorn, huckleberry, poplar, rhododendron, and willow.

Residential Recommendations

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Chemical control of the azalea bark scales and their eggs in the ovisacs is difficult with insecticide sprays. However, after the eggs hatch, the tiny, new nymphs are exposed on the bark and relatively vulnerable. Late spring and late summer are the two best times to treat. Imidacloprid, pyrethroids, or summer oil should give adequate control of the nymphs, especially nymphs that have not secreted the white, matted covering. When used as directed, pyrethroids are very toxic to insects but are not particularly hazardous to humans and pets (other than fish-avoid using pyrethroids around pools, ponds, and streams).


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Publication date: April 21, 2016
Revised: Aug. 29, 2019

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