Friday, April 3, 2009

Landscape - Scale Insects: Azalea Bark Scale

This is the first in a series on scale insects in the landscape. It is a description of the Azalea bark scale. Information is from the University of Maryland.

Azalea Bark Scale (Acanthococcus azaleae), Family Erioccicdae

Plants Damaged: This scale is a pest of azaleas and rhododendrons. This scale has been reported on hawthorn, Andromeda, poplar, willow and ornamental cherry trees.

Damage Symptoms: Azalea bark scale has become recognized as a prominent pest of azaleas. Infested plants usually appear chlorotic and unthrifty. Infested plants are often covered with sooty mold, a black fungus that grows on the honeydew excreted by the azalea bark scales as they feed. Eventually twigs may die back.

Life Cycle: As the female azalea bark scale matures, it secretes white, waxy threads, which become felted or matted into a thick covering over its entire body. Females lay eggs in this white wax. As the female lays eggs, its body shrivels gradually as the egg sac fills with eggs. Eggs are laid in May. They hatch in central Maryland in late May to early June. Individual crawlers are active and moving for 12 – 24 hours. New crawlers continue to emerge over a couple of weeks. There are two generations in Maryland. This new generation matures during the summer and produces eggs in September. Mature females tend to feed in crotches and on twigs. Adult males, two-winged and tiny, tend to feed on the leaves. Azalea bark scale overwinters as immatures in the forks of the twigs.

Control: If the population is low and damage is minimal, look for beneficial insects which do a good job controlling this insect. If necessary, apply a dormant spray for overwintering nymphs on twigs. In summer when crawlers are active, you can use a summer rate (0.5 – 1.0%) of horticultural oil for control.

Azalea bark scale. Photo from the United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service,

Azalea bark scale crawler activity.

Information from "Scales Commonly Encountered in Maryland Landscapes and Nurseries" by Stanton Gill, Extension Specialist in IPM for Nurseries and Greenhouses,and Suzanne Klick and Shannon Wadkins, Technicians, Central Maryland Research and Education Center University of Maryland Cooperative Extension.

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