Armored Scale Species
Euonymus scale is usually found on lower branches or on the new leaves of several species of euonymus, bittersweet, and pachysandra. The male scale produces a small, thin, white covering and can be quite numerous on the undersides of leaves. The female scale lives under a gray or brown shell and is usually found on the branches. The female scale overwinters under its protective shell and deposits eggs in early spring under the scale covering. The eggs hatch into yellow-orange colored crawlers over a two-to-three week period in late May or early June. As the nymphs develop, they crawl to other parts of the host plant to feed, although they can be blown to other susceptible hosts. Once they start feeding, they quickly begin to produce the hard protective covering as they grow. Two generations are commonly produced per year.
Oystershell scale found in our area is either the gray race or the brown race. Host plants include ash, dogwood, lilac, maple, and willow. The oystershell scale adult armor is light to dark brown and shaped like a tiny oystershell. The scale overwinters in the egg stage under the females’ protective cover. Two generations are produced per year. Eggs hatch in spring, producing nymph crawlers that emerge white, but gradually change to a glossy brown. By mid July, the scale is fully grown. A second generation follows in late August or early September.
Pine needle scale
Pine Needle Scale is probably the most common armored scale found on conifers in the United States and Canada. The white, oystershell-shaped scale can completely cover needles causing plant discoloration, needle yellowing, and even branch death. This scale settles on the needles of its host and forms a 1/8-inch white, oystershell-shaped cover. Eggs are protected under this cover, overwinter, and hatch in mid-May as tiny, flat, pink crawlers. These crawlers search for suitable needles on which to feed and once settled, begin to form their protective armor. Males molt into a prepupa for a week and then emerge as winged adults. Females, however, molt into wingless nymph-like adults. After mating, the females lay eggs under their protective shell. There are two generations each year.
Soft Scale Species
European elm scale
European elm scale males and females differ considerably in appearance and life cycle. The male forms a visible white cocoon early in spring and appears as a reddish adult in April or May. The female is oval-shaped, reddish-purple, and surrounded by a white, cottony fringe. The female deposits her eggs beneath herself on a twig of the host plant. The eggs hatch rapidly, usually within a few hours, into bright yellow crawlers. The crawlers then migrate to feeding sites along the midrib and other prominent veins on the underside of leaves. Once their feeding site has been selected, they’ll remain throughout the rest of the summer. In the fall, the crawlers return to a limb or trunk crevice where they hibernate as nymphs (immature females). Hibernating females often resemble small mealy bugs: oval-shaped and covered in short, white, waxy filaments. All native elms are susceptible to this scale. There is one generation per year.
Fletcher scale is common in the northern parts of the Midwest and Canada and is most frequently found on arborvitae (Thuja sp.) and yew (Taxus sp.). Pachysandra and Eastern red cedar are also susceptible. Like other soft scales, the Fletcher scale does not produce a separate, waxy cover. Instead it secretes a thin, transparent film, which does not totally cover the insect. The amber to reddish-brown nymph overwinters on a branch. The following spring, it feeds heavily as it grows into an adult. At maturity, a single female can produce 500-600 eggs in May, which hatch in late June or early July. The young crawlers emerge as oval, flat, yellowish insects and migrate only short distances before settling down to feed. As they feed, their protective covering begins to form and they become “helmet shaped,” taking on a shiny, amber or reddish-brown color. One generation per year is produced.
Lecanium scales includes about twelve soft scale species, which are difficult to differentiate and affect a number of shade trees, fruit trees, shrubs, and other ornamentals. The scales can vary in length from 1/8-to-1/2-inch, depending on species. Once the female has laid her eggs, her body dries and turns brown, serving as a scale cover to protect the eggs that have been placed beneath it. Eggs hatch beneath the females in late spring or early summer, and crawlers then migrate to leaves of the host plant to feed. Excessive amounts of honeydew can attract black sooty mold fungus. In late summer, immature females return to twigs to overwinter. There is one generation per year.
Magnolia scale is our largest soft scale insect, reaching ½ inch in length. This scale spends the winter on one-to-two-year-old twigs as tiny, dark-colored nymphs. In the spring, the scales begin to feed, mature, and change color. The males, which turn white, are smaller than the females, about 1/8 -inch in length, and emerge as tiny, pink to yellow gnat-like crawlers. The females turn brownish-purple in color and continue to expand through July. Magnolia scale eggs hatch internally, and the crawlers are born alive. Crawler emergence occurs in the fall. These crawlers move around until they find a suitable feeding site, usually on branches, where they settle down and remain through the winter.