Scale insects

By The Old House Web

Scale insects

List of files and visuals associated with this text.

Proper plant care, including pruning of heavily scale- infested branches, is a primary management strategy for scale insects. With certain host plant/scale combinations, however, supplemental controls are needed.

Most scales overwinter on the plants as eggs underneath the female scale covering. Many of these can be killed by dormant oil sprays applied in spring before egg hatch. Dormant oil applications every few years are capable of controlling all but the most stubborn scale problems. Some phytotoxicity or other undesirable effects may result from use of dormant oils in inappropriate situations. For example, the waxy "bloom" on blue spruce may be removed by such a treatment.

Controlling scale insects with insecticide sprays requires timing the application to coincide with scale egg hatch. The brief period after egg hatch is the "crawler" stage of the scale, when the insect is mobile and has not yet produced a protective waxy coating. When the crawler stage occurs differs with the scale species and the weather. After the insect settles and secretes wax, it is largely impervious to insecticides.

Some insecticides with systemic activity (such as Orthene or acephate) can be injected into plants or used as a soil treatment to kill established scale insects. These materials generally are translocated within the plant in highest concentrations to the newer growth.

Armored scales

Many people do not recognize these scales as insects. Instead, they think they are part of the tree or shrub itself. This is understandable because armored scales are small (1 to 2 mm), permanently attached, hard, flat, circular to elongate, crusty scales. Mature scales lack a distinct head, legs or antennae. Eggs mature underneath the female scale. The first larval stage hatching from the egg is called the crawler stage. This is the only mobile life stage other than the adult male, which is rarely seen and lives only a few days. Crawlers move about for several days before permanently settling down on the plant to feed. Crawlers and very young scale insects are the life stages most susceptible to insecticides.

Soft scales

These scales have a life cycle similar to that of armored scales. Soft scales are frequently much larger (up to 6 mm) and softer bodied, and some may move about as adults. Many soft scales are hemispherical and dark. A related group of scales produces cottony wax and includes the cottony maple scale.

Visuals associated with this text.

Visual title - Visual size Visual title - Visual size
Scale on hibiscus - 39K Tea scale on camellia - 41K
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