Scale is one of the most common insect pests of Euonymus. These tiny insects take up residence on the stems and leaves of most of the Euonymus species, especially the evergreen forms. The winged euonymus (E. alatus) is not usually susceptible to scale.
Many different species of scale infest these shrubs but the most common is the euonymus scale, Unaspis euonymi.
Males of this species are tiny, narrow, and white. They are generally more abundant than the females and tend to coat both the stems and the leaves. Heavy infestations can make the shrub appear almost white even from a distance. The females are brown and oyster-shaped. They are about twice the size of the males and are primarily found on the stems.
Scale insects feed by sucking juices from the plant with thread-like mouth parts. This causes damage to the stem and yellow stippling of the leaves. Eventually leaves are damaged enough that photosynthesis is reduced and in severe cases, leaf drop and the death of infested branches occurs. Heavy infestations may kill the entire plant.
Fertilized adult females overwinter on the stems of the plants. They lay their eggs in the early spring under the protection of their hard waxy shell. After the eggs are laid, the females die. The tiny crawler stage hatches from the eggs in April, May, and June. This stage is the most vulnerable to pesticide treatment because the crawlers are not protected by the hard waxy shell of the adult stage. These small nymphs crawl around the leaves and stems of the plant and mate before settling down to feed through mouth parts inserted into the plant tissue. At this point, they become sedentary and secrete their hard waxy shell. There may be up to 3 generations per year depending on the area of the country and at times all life stages may be present on a plant at the same time.