Euomymus Scale (Unaspis euonymi)

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.

Euonymus scale

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.

Life Cycle of Euonymus Scale

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.

Control Measures -

• Natural predators like the lady beetle do an excellent job at suppressing heavy infestations of scale insects.
• If the problem isn't extensive, infested branches can sometimes be pruned out but if a shrub is repeatedly infested year after year, it may be wise to remove it and replace it with a more resistant variety.
• If chemical treatment is necessary, the timing of the application is important. The best time to control euonymus scale and other species of armored scale is when they are in the crawler stage since at this point they are not protected by a shell. Killing the first generation of crawlers (April, May, and June) provides the best control because at the time these hatch, the adults from the previous year have already died. 
  
  • Horticultural oil sprays are very effective in killing the crawlers. Bonide All Seasons Oil and Pure Spray Green (from the makers of Clear Choice) are good choices. It is imperative to coat every surface of the plant (all sides of the leaves and stems) in order to achieve the best control.
  • Systemic insecticides such as Bayer Advanced All-in-One Rose & Flower Care and Bonide Annual Tree and Shrub also provide effective control of crawlers and will also help suppress the adult stages of the scale insect. 

Recommendations and pesticide use may vary depending on on the state you live in.

Read the label before applying any pesticide.