Scale insects are small, immobile insects with no visible legs or antennae, pressed tightly against the plant on which they are feeding. Many are common and serious pests of trees, shrubs and indoor plants. Scale Insects are separated into two groups, Armored Scales and Soft Scales
Scale insects can be roughly divided into two groups: armored scales and soft scales. Armored scales secrete a protective cover over their bodies. Most species of armored scales overwinter as eggs beneath the female cover. In spring, these eggs hatch into tiny mobile crawlers which migrate to new feeding sites. The crawlers settle after a few days, insert their mouthparts in the plant, and begin to feed. Soon they secrete a protective cover and lose their legs. Large populations can build up before plants begin to show visible symptoms. Most common armored scales are. San Jose Scale, Oystershell Scale, Pine Needle Scale, Euonymus Scale, Juniper Scale, Hemlock Scales
In general, soft scales are larger and more convex than armored scales. Many resemble miniature tortoise shells. Soft scales usually cover themselves with wax, but they lack the detachable protective cover for which armored scales are named. Most soft scales overwinter as immature, fertilized females. In spring they resume feeding, mature and lay eggs. These hatch into tiny crawlers. After locating suitable feeding sites, crawlers settle and begin feeding. Some species lose their legs once they've settled; others retain legs and are able to crawl short distances to find suitable overwintering sites in the fall. Except for those soft scales which infest indoor plants, most have only a single generation per year at our latitude. Our most common soft scale pests are described and illustrated below, Magnolia Scale, Fletcher Scale, Cottony Maple Scale, Oak Kermes Scale
Scale insects feed on plant sap. They have long, threadlike mouthparts (stylets) which are six to eight times longer than the insect itself. Scale feeding slowly reduces plant vigor; heavily infested plants grow poorly and may suffer dieback of twigs and branches. An infested host is occasionally so weakened that it dies. Scales often secrete a sticky honeydew which is attractive to wasps and ants and which supports the growth of black sooty molds.
Scale insects are generally controlled by natural enemies, including tiny parasitic wasps and predators such as ladybugs. It is very common for ladybugs to move onto a plant with a growing scale infestation; before deciding upon treatment, look for adult and immature ladybugs on your plants. Dormant oil treatments can be used against almost all scale problems and are generally applied in very early spring, before bud break. Summer oils can also be very effective against most scales, but as with dormant oils, some plants are sensitive to these treatments. Check labels to make sure your plant is not harmed by the oil treatment you are considering. Most other insecticides, including insecticidal soaps, can be used only against the mobile crawler stage of scales since adult scales are protected from insecticides by a waxy covering. These treatments are very effective, but must be carefully timed as crawlers are only active for a limited period.