Scale insects are a peculiar group and look quite different from the typical insects we encounter day to day. Small, immobile, with no visible legs or antennae, they resemble individual fish scales pressed tightly against the plant on which they are feeding.
Scale insects feed on plant sap. Feeding by scales slowly reduces plant vigor. Heavily infested plants grow poorly and may suffer dieback of twigs and branches. Occasionally, an infested host will be so weakened that it dies. Sooty Mold a fungus often grows on the excrement of the insects. This is black in nature and can not be mistaken.
During the summer, control requires accurate identification of the pest species so that hatching dates of crawlers can be determined. Once the pest is identified and proper timing known, any one of several common insecticides can be used. We also use systemic insecticides with a foliage application or soil injection depending on severity of infestation. This increases the window of control.
Scale insects can be roughly divided into two groups: armored scales and soft scales. Armored scales are so named because they secrete a protective cover over their bodies. Most species overwinter as eggs beneath the female cover. In spring, eggs hatch into tiny mobile crawlers which migrate to new feeding sites. After a few days, crawlers settle, insert their mouthparts, and begin feeding. Soon they secrete a protective cover and lose their legs. Large populations can build up unnoticed before plants begin to show visible symptoms. Our most common armored scale pests are described and illustrated below.
These scales are shaped like the shell of an oyster. They are chestnut to dark brown, sometimes with lighter transverse bands. Twigs are often completely encrusted with scales. This is a common and destructive pest of over l20 different species of fruit trees, shade trees, and woody ornamental shrubs. Hosts include apple, lilac, dogwood, boxwood, birch, elm, sycamore, viburnum and many others. There are two generations per year with crawlers active May l-20 and July l5- 25.
Mature scales are pure white and shaped like oyster shells. This is a common and serious pest of ornamental pines and various spruces. Less preferred hosts include hemlock and fir. Ornamental plants, Christmas tree plantations, and nursery stock are more frequently infested than forest trees. In heavy infestations, needles may be completely whitened by a continuous layer of scales. Crawlers are active between April 20-May 30 and July l0- 20.
Females are pear-shaped and blackish-brown. Males are elongate and white. This is a common and serious pest of evergreen euonymus, often causing defoliation and dieback. Pachysandra and bittersweet are also suitable hosts. There are two generations per year. Crawlers are active May 5-June l0 and August l-25. .
Females are round and dirty-white with yellow centers. Under a magnifying glass they resemble miniature fried eggs. Males are also white, but smaller and narrower. Hosts include junipers, arborvitae, incense cedar, and cypress. There are two generations annually. Crawlers are active April 5-20 and June 5-20.
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, but others retain them and are able to crawl short distances to find suitable overwintering sites in the fall. Except for 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:
Our largest scale insect, this species reaches l/2 inch in length. Color ranges from dark brown to pink-orange and older scales are covered with a white waxy powder. Large amounts of a sticky waste product called honeydew are secreted by the scales. Wasps and ants are attracted to the honeydew and black fungi called sooty molds grow on surfaces where honeydew collects. There is one generation per year with crawlers active from September l-20, much later than most other species.
Dormant oils are effective on the overwintering stage of most species, but they can only be applied in early spring before leaves appear. Adult scales are protected from insecticides by waxy coverings. Control measures, therefore, must be aimed at unprotected immatures (crawlers) or the overwintering stage.
Pine Needle Scale
European Fruit Lecanium
This is our second largest scale, reaching l/3 inch in length. Color varies from gray-green to pink-orange, mottled with black. It is easily mistaken for magnolia scale but lacks the white, waxy powder. Both tulip tree and magnolia are attacked and may be seriously weakened. Large amounts of honeydew are produced. There is one generation per year with crawlers active September l-20. A single female can produce over 3000 young!
Mature scales are shiny, dark brown, and very convex. They are similar in appearance to European fruit lecanium and oak lecanium which are close relatives. Arborvitae and yew are the most frequently attacked hosts, but pachysandra and Eastern Red cedar are also susceptible. Honeydew excreted by the scales supports unsightly, sooty molds. There is one generation per year with crawlers active June 5-25. When necessary, treat between June l0-l5.
Typical scales are l/8 inch long, oval, and very convex. Color varies considerably with age and host, but usually they are brown to reddish-brown, smooth and shiny. The host list of this insect includes a wide range of fruit and shade trees, shrubs, and other woody ornamentals. Favorite hosts include peach, cherry, plum, apple, ash, blueberry, black walnut, boxelder, elm, grape, hickory, locust, magnolia, maple, oak, redbud, willow, and many others. There is one generation per year with crawlers active between June l-20.
Long, white, cottony egg sacs produced by this scale are much more conspicuous than the scales themselves. After completion of the egg sac, the female dies, dries up, and falls to the ground. Host plants include camellia, holly, taxus, rhododendron, hydrangea, maple, and English ivy. There is one generation per year with crawlers active June l-l0. When necessary, treat June l0-20.
Cottony Camellia Scale, Cottony Taxus Scale
Cottony Maple Scale
Cottony Maple Leaf Scale
Large, conspicuous, white egg sacs are produced on the twigs and small branches of host plants. Conspicuous, cottony egg sacs, similar to cottony maple scale, but produced on the leaves. Occurs on maple, dogwood, holly, andromeda, and gum. There is one generation per year with crawlers hatching June l-l0. When necessary, treat between June l5-30.
Large, conspicuous, white egg sacs are produced on the twigs and small branches of host plants. During summer, immature scales feed on leaves, but they migrate to twigs as fall approaches. Honeydew excreted by the scales supports unsightly, sooty mold growth. Cottony maple scale is most common on silver maple, but also found on other maples, boxelder, linden, black locust, red mulberry, white ash, apple, beech, cherry, dogwood, elm, hickory, holly, honeylocust, peach, plum, sycamore, willow, and others. There is one generation per year with crawlers active June 5-25. When necessary, treat on both June l0 and 20.