Arborvitae scales (Carulaspis miniena) not only attack arborvitae but probably all the junipers listed below. The females are roundish shape and are white with a dark center. The males are somewhat elongated and are whiter. The crawlers emerge over a two-week period in May.
Juniper scale (Canulaspis juniperi) is often difficult to detect - often requiring strong magnification to see them. This scale is known to commonly attack eastern red cedar, Savin and Pfitzer junipers. Symptoms may be confused with other problems. The first indication that there is a problem is the loss of the dark lustrous coloring of the foliage. New growth does not occur on infected twigs. As feeding damage increases, the foliage becomes yellowish and then turns brown as it dies. The scale can kill entire plants when not brought under control. There is one generation a year. The cover on the female is white. Eggs hatch and crawlers emerge in late May to early June. Crawlers' emergence lasts for four to five weeks.
Crawlers of both of these scales move to other areas on the plant to feed. In addition, they are light enough for the wind to blow them to other host plants. Field diagnosis is almost impossible. Microscopic examination is required for correct identification. It is believed that the Arborvitae scale is more common in the south. However, records of their distribution are not always considered reliable.
Scale infestations on juniper frequently stay small, so treatment is usually not needed. High populations can be treated with a dormant oil spray in early spring. Use the lowest recommended rate of application. Crawler sprays are also effective.
Written by James Schuster, Extension Educator, Horticulture, and reviewed by Philip L. Nixon, Extension Specialist-Entomology, Department of Natural Resources and Environmental Sciences University of Illinois at Urbana-Champaign.
Filed under plants: Evergreen Trees & Shrubs