Armored and Soft Scales
Scales (Superfamily Coccoidea) are a diverse group of sucking insects that are common pests of trees and shrubs. Scale insects are unusual in that the adults secrete a shell-like layer that covers all or most of the entire body. This covering protects the insect from predators, parasites, and adverse environmental conditions.
There are two major families of scale insects: soft and armored. The shell of soft scales typically is prominent, and is characterized by a thick waxy coating. Soft scales typically are round or oval, often hemispherical, and are 1/8 to 1/2 inch in diameter. Soft scales, like aphids and whiteflies, secrete honeydew; when infestations are heavy, infested plants will be covered with large amounts of this sticky substance.
In contrast, armored scales are covered with a thin, ‘hard’ shell that doesn’t have the thick wax characteristic of the shell of soft scales. Armored scales range in size from 1/16 to 1/8 inch in length; females typically are larger than males. Armored scales can be circular, oval, oblong, thread-like or pear-shaped. Armored scales do not secrete honeydew.
Signs of damage:
Scales attack hundreds of ornamental varieties, and are found everywhere ornamental plants are grown. While some scales infest a wide variety of plants, others are host-specific. Many ornamentals are attacked by a single scale species, while others are attacked by numerous species.
Scales damage plants by sucking the juices from the plants. Heavily-infested plants appear unhealthy and produce little new growth. Scales that feed on leaves can cause leaf spotting; spots progressively increase in size as the scales continue to feed. With serious infestations, leaves drop prematurely, and twigs and branches may be killed. The sooty mold that develops on the honeydew produced by soft scales inhibits the plant’s ability to harvest light energy, reducing photosynthesis and further weakening the host plant. Scales that feed on twigs or bark generally do not produce leaf discoloration, but long-term feeding weakens the host plant. A chronic infestation can kill the host.
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