There are several species of scale insects that damage different ornamental plants in West Virginia. These insects feed by sucking the plant juices, generally, causing the plants to become unhealthy in appearance. Often the affected plant will have a sooty-black appearance. This is due to the fact that scale insects excrete a sticky material called "honeydew" upon which saprophytic fungi, called sooty mold, develop.
Scale insects are often quite conspicuous on plants and may give the plant an overall whitish appearance. The scale coverings of the insect may be leathery, waxy, cottony, hard or mealy.
The insect passes through three developmental stages--the egg, the nymph, and the adult. During a part of the nymphal period the scales move about on the plant. This period is called the "crawler" stage. Once the crawlers settle down and insert their thread-like mouthpart into the plant they cannot move again.
Scale insects are generally not vulnerable to insecticides except during the "crawler" stage because of the protection provided the insect by the scales. The only other time that control measures can be applied is in the dormant period, before new growth begins.
Specific Scale Insects
Azalea Bark Scale (Eriococcus azaleae)(Comstock)--Scales are oval, cottony insects that may appear on twigs and leaves. Their feeding causes plants to become unhealthy in appearance.
European Elm Scale (Gossyparia spuria)(Modeer)--When abundant, these insects give a white appearance to the limbs and crotches of the tree. Females, that occupy natural depressions in the bark, are oval scales with brown bodies fringed with a white, cottony material. They excrete large amounts of "honeydew" that drops from the tree.
Euonymus Scale (Unaspis euonymi)(Comstock)--This insect, when abundant, looks like frost on green leaves and stems of Euonymus, Bittersweet and Pachysandra. Female scales concentrate on stems and are roughly pear-shaped, brownish, and about 1/16 inch long. Males, which are white and narrow, congregate in large numbers on the undersides of leaves. Immature scales, or "crawlers," appear as golden specks on leaves. There are two generations per season.
Holly Scale Insects--Several species of scale insects may infest the bark and reduce, the vitality of the plant. One species causes pits to form in the bark.
Juniper Scale (Carulaspis juniperi)(Bouche)--Junipers with heavy scale infestation appear sickly. Foliage may have a grayish appearance. Female scales are circular, convex, and gray with a small yellow center. Males are smaller, narrow, and white with a ridge down the center. The insects overwinter in nearly full grown condition. Egg laying begins in May and the new brood appears about mid-June. There is only one generation per year.
Oystershell Scale (Lepidosaphes ulmi)(L.)--These armored scale insects, resembling miniature oyster shells, may encrust the bark of various limbs and occasionally an entire tree. The insect overwinters in the egg stage under the female scale. "Crawlers," appear in May. Occurs on lilac, maple, poplar, and willow.
Magnolia Scale (Neolecanium cornuparvum)(Thro)--Insects are large, brown soft scales that may appear white, due to a waxy cover over the shell. Infected trees have a sickly, dirty-black appearance, due to excretion of "honeydew" upon which sooty mold develops. The bluish "crawlers" overwinter on bark.
Cottony Maple Scale (Pulvinari innumerabilis)(Rathvon)--This scale insect is rather conspicuous during the summer on maple due to large, white, cottony egg sacs on the end of the females. Adult females overwinter on twigs. "Crawlers" (Nymphs) are abundant in early July. Heavy populations of this insect seldom occur due to beneficial insects that attack it.
Golden Oak Scale (Asterolecanium variolosum)(Ratzeburg)--These circular, greenish-gold scales, about 1/16 inch in diameter, make "pits" in the bark of oak. Young scales appear in the spring. There is only one generation per year.
Pine Needle Scale (Chionaspis pinifoliae)(Fitch)--These are small, white elongated scales that infest needles. Heavily infested trees are pale yellow and have an unhealthy appearance. Insects overwinter as eggs beneath the scale covering. Two broods occur, one in May and another in July.
Rose Scale (Aulacaspis rosae )(Bouche)--These scales are frequently found in masses on the bark at the base of the plant. Females are white, circular, and about 1/8 inch in diameter. Males are long and narrow, with three ridges running lengthwise on their backs. The insect overwinters as eggs.
Tuliptree Scale (Toumeyella liriodendri)(Gmelin)--These are large, hemispherical, brown scale insects that suck sap from branches and limbs. The scales secrete much "honeydew," upon which sooty mold develops, giving the leaves and branches a black, unsightly appearance. They overwinter as partly-grown nymphs on the bark.
