There are many different types of scale insects. The following kinds represent some of the most commonly occurring in Michigan. Scale insects can eventually kill your plants, trees and shrubs. areas.

Oystershell Scale

This insect's waxy covering resembles a tiny oystershell. Most are gray, although there is a brown-colored type. Oystershell scales occur on most deciduous shrubs and trees but cause the most injury to lilacs and cotoneaster. The insects may become so numerous that stems are encrusted. Continued sap feeding by scales can cause branches to become spindly and leaves to turn yellow, eventually killing the plants. Eggs pass the winter under the protective covering of the dead female scale, hatching from late May to mid June. Young scale insects are called "crawlers" and have legs that allow them to move to the new growth. Here they begin feeding by inserting a thread-like feeding tube through the bark. They lose their legs when they shed their first skin, a process called "molting". Young scales then secrete a protective covering.

Oystershell scale Photo:  USDA Forest Service Region 2 Rocky Mt Region Archive Bugwood.org

The most effective control strategy is to spray two to three times at about weekly intervals with insecticides, beginning at egg hatch, when crawlers first appear.

Pine Needle Scale

Mature scales are small, slender, and chalky white. The female is nearly twice the length of the males. Heavy infestations on pine and spruce trees cause needles to become yellow, and can kill individual branches. The insect winters in the egg stage under the female scale covering. Eggs hatch about when the new growth appears in the spring. Newly hatched crawlers move to green needles, begin feeding, and produce the typical white covering.

There may be two generations in Michigan,  the first hatching in early to mid June, and the second in late July or early August. Use insecticides during the hatching period when crawlers are observed for maximum effectiveness.

Euonymus Scale

Male scales are small, slender, and chalky-white. Females are pear shaped, brown, and about twice the size of males. Euonymous scale is found on all varieties of Euonymous, and will infest a few other types of shrubs. The insect attacks both stems and leaves. Stems often become so heavily encrusted with scales that they appear white. Shrubs can be killed if scale is not controlled.

Mature female scales overwinter on the host plants. Eggs laid under the scales in early spring hatch in late May and early June. During the summer, ail stages can be found at any time, therefore it is possible to have 2 or 3 overlapping generations each year.

Detecting Crawlers

Control will be most effective if insecticide sprays are applied when the crawler (newly hatched) stage is present. Scale crawlers are minute, yellow, oval shaped insects. They are barely visible to the unaided eye, so regular examination should be made with a magnifying glass. Crawlers are mobile only during the first stage of development. This stage has a duration of 7 to 10 days.

Oystershell scale Photo:  USDA Forest Service Region 2 Rocky Mt Region Archive Bugwood.org

Pine Needle Scale Photo:   Scott Tunnock USDA Forest Service Bugwood.org

Photo:  John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org