Scales are major insect pests of trees and shrubs grown in landscapes and nurseries. Certain scales feed on only one plant type, whereas other scales may feed on many different plant species; for example: magnolia scale, Neolecanium cornuparvum, and tuliptree scale, Toumeyella liriodendrii. These two scales are often mistaken for each other because they look similar. Magnolia and tuliptree scale are two of the largest scales in the United States. Both are soft scales with piercing-sucking mouthparts and produce large quantities of honeydew. However, magnolia scale is specific in that it attacks only magnolia, including Magnolia stellata and M. soulangeana, whereas tuliptree scale has a broader host range, attacking magnolia, tuliptree, walnut, and linden.
Magnolia scale females are 1/2 inch long and red-brown in color. They are initially covered with a white, waxy powder. In August and into September (depending on the temperature), females produce eggs, which hatch into crawlers that are gray to red. Crawlers are active in September and move around before settling down to feed on twigs. The crawlers are usually located on the undersides of 1-to-2-year-old twig growth. They eventually produce a powdery, waxy white covering over their bodies. Magnolia scale overwinters as a first-instar crawler. There is one generation per year in Illinois.
Tuliptree scale females are also 1/2 inch long and vary in color from gray-green to pink-orange, with black mottling. Also, there are ridges on the edge of the body. Females have a high reproductive capacity, producing more than 3,000 crawlers over 2 to 3 weeks. Crawlers are black and move around on plants before settling on twigs in the fall. They are normally active from August through September. Tuliptree scale overwinters as a second-instar crawler. Similar to magnolia scale, there is one generation per year.
Infestations of either scale can cause branch dieback, plant decline, and possibly even plant death if repeated heavy populations occur. Also, the excessive amount of honeydew produced by the scales may attract other insects, including wasps and ants. Large quantities of honeydew serve as a growing medium for black sooty mold, which reduces a plantís ability to manufacture food through photosynthesis.
Treat for magnolia scale in late September, when the crawlers are most active. It is now too late to treat for the active crawlers of tuliptree scale; however, a dormant oil spray may be performed in late fall or winter to kill the overwintering crawler stage. Insecticides recommended for managing both scales, primarily targeting the crawler stage, include acephate (Orthene), insecticidal soap, and summer oil. It is important to cover all plant parts thoroughly. The primary way to minimize problems with scales is by promoting plant health through proper irrigation, fertility, mulching, and pruning practices. This reduces susceptibility or limit the injury from both scales.
Although there are natural enemies, including ladybird beetles, that feed on scales, they are not usually present in numbers high enough to provide sufficient control.