PEST 411
Prune now to reduce infestation Scout for scale insects on azalea bark
by Shimat V. Joseph, Department of Entomology, University of Georgia
Azalea bark scale (ABS) (Eriococcus azaleae) (Fig. 1) poses a serious threat to azaleas, rhododendron, and pieris or andromedas in Georgia. They are also reported on blueberry, hawthorn, huckleberry, poplar, and willow. Often, ABSs are mistaken for mealybugs because of their elongated, white-fussy appearance. ABS is a soft scale, meaning the nymphs and females secrete waxy crust (protective coating) on their body and cannot be separated from the scale insect, unlike armored scale insects. Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Fig. 1. Females of azalea bark scale.
Lifecycle
Females of ABS lay purple-colored eggs in white, feltlike eggmasses or ovisacs during the spring (Fig. 2). The purple-red colored females reside inside the ovisac, which is about 3 mm long. The eggs hatch by midMay. The egg hatch may last for two to three weeks in May. The first nymphal stage of the ABS is referred to as "crawlers," which emerge from the eggs. The redcolored crawlers are the only mobile stage of the ABS as they have legs and antennae. The crawlers also lack the white crust covering. They walk around searching for a suitable spot to settle. When they find a crack or crevice on the bark surface, they settle on those areas and begin feeding by inserting their long, thread, or needle-like mouthparts into the bark, reaching phloem tissue. Phloem tissue is where the food is transported within the plant, and it runs along the stem beneath the bark. They are also found in areas where the azalea branches fork. They shed their legs and antennae and grow into the 2nd and 3rd nymphal stages. The scale can undergo two generations per year in Georgia. The females mature by September, and they lay eggs in the ovisacs. The emerging, secondgeneration ABS nymphs overwinter within the cracks and crevices in the stem (Fig. 3).
24 | UAC MAGAZINE
Damage
When azaleas lose leaves or experience branch dieback, ABS could be the reason. Sometimes the leaves will turn yellow, especially on the dying branches (Fig. 4). The white crusts of the scale insects will be visible on branches. The developing nymphs and females excrete sugary, syrupy liquid on the bark and leaves, often called honeydew. As time passes, the surface of the bark and sometimes the leaves turn black because they get infected with a black sooty mold fungus (Fig. 5). This fungus feeds on the sugary secretions on the surface of the bark and leaves. At this point, we usually notice that the azalea plants look different and have some serious problems. The white crusts of scale insects are easily visible when the azalea bark completely turns black (Figs. 6 and 7). The ABS infestation rarely kills the plant, but can kill if the infestation is extremely severe and not controlled.
