We have received several inquires over the past week regarding tuliptree scale (Toumeyella liriodendrii) and magnolia scale (Neolecanium cornuparvum). The two scales are often mistaken for each other because they look similar. Tuliptree and magnolia scales are two of the largest scales in the United States. In addition, both are soft scales with piercing-sucking mouthparts, and both produce large quantities of honeydew. However, magnolia scale attacks only magnolia (for example, Magnolia stellata and M. soulangeana), whereas tuliptree scale has a broader host range, attacking not only magnolia but also tuliptree, walnut, and linden.
Tuliptree scale females are 1/2 inch long and vary in color from gray-green to pink-orange, with black mottling. In addition, there are ridges on the edge of the body. Females are capable of producing more than 3,000 crawlers over a period of 2 to 3 weeks in August and/or September. The crawlers are black and migrate on plants before settling on twigs in the fall. They are primarily active from August through September. Tuliptree scale overwinters as a second-instar crawler. There is typically one generation per year in Illinois.
Magnolia scale females are 1/2 inch long and red-brown in color. They are initially covered with a white, waxy powder. In August, females produce eggs, which hatch into crawlers that are gray to red. The crawlers are active primarily in September. They crawl around before settling down to feed on twig growth. Crawlers are usually found on the undersides of 1- to 2-year-old twig growth. The crawlers eventually produce a white powdery wax covering over their bodies. Magnolia scale overwinters as a first-instar crawler. Similar to tuliptree scale, there is generally one generation a year in Illinois.
Infestations of both tuliptree and magnolia scale can cause branch dieback, rapid plant decline, and even plant death if repeated heavy populations occur. In addition, the large amount of honeydew produced by both scales may attract other insects, including wasps and ants. The honeydew also serves as a growing medium for black sooty mold fungi, which reduces the plant's ability to manufacture food through photosynthesis.
Treat for magnolia scale in late September, when the crawlers are most active. It is 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. Pest-control materials recommended for managing both tuliptree and magnolia scale, primarily targeting the crawler stage, are acephate (Orthene), insecticidal soap, and summer oil. It is important to thoroughly cover all plant parts. In addition, maintaining plant health by proper irrigation, fertility, and mulching practices may reduce susceptibility or limit injury from both these scale pests.
Tuliptree scale is susceptible to natural enemies, including ladybird beetles; but they are not usually present in numbers high enough to provide sufficient control.