Magnolias are a family of approximately 80 large shrubs and trees native to Asia and North America. Several ornamental species include the southern magnolia (Magnolia grandiflora), which grows around 90 feet tall and has glossy dark-green foliage; cucumber magnolia (Magnolia acuminata), a 60- to 80-foot-tall variety with light green leaves; and star magnolia (Magnolia stellata), which grows around 20 feet tall. Scale insects commonly feed on magnolia trees and shrubs.
Magnolia Scale Identification
The magnolia scale (Neolecanium cornuparvum) is a large type of scale that can grow half an inch around when mature. Adult females and immature nymphs do not have evident heads, legs, wings or other moving body parts. The adult females have brownish- or pinkish-orange coverings that are coated with a powdery white wax, while the nymphs are greyish-black. Magnolia scales are soft scales; their covering is a part of the body and cannot be separated from the insect. Adult males are only around an eighth of an inch long and can fly; they have yellowish- or pinkish bodies.
Other Scale Pests
Several other types of scale also infest magnolia. Oleander scales (Aspidiotus nerii) are around 0.1 inch long; this armoured scale has a plated cover that protects its soft body, but the plating can be removed from the insect. Oleander scales have light-coloured coverings with a brownish or yellowish spot in the middle; beneath the plating, their bodies are yellow or yellowish-brown. Greedy scales (Hemiberlesia rapax) are around the same size as oleander scale; their conical plates have a black spot in the middle. California red scales (Aonidiella aurantii) are approximately 0.08 inches and have reddish-brown coverings.
California red scale, greedy scale and oleander scale rarely cause serious harm to magnolia trees; magnolia scales, however, attack and damage stressed plants. They primarily feed on species such as star, lily, saucer and cucumber magnolia. Magnolia scales attach their mouthparts to branches and drain sap from the tree. Severe infestations cause slow leaf and twig growth, branch death and can even kill trees. They also exude large amounts of a sticky substance called honeydew that drips down on the lower foliage. A black fungus called sooty mould forms on the honeydew.
You can control scale infestations by carefully checking new magnolia trees before purchase, since most scales enter the landscape on infested plants. Some species of lady beetles also feed on scale. Scale insects feed on stressed plants, so water and fertilise your trees as needed to keep them healthy. Treat infested plants by removing severely infested branches and by applying horticultural oils or insecticidal soaps. You can also use traditional insecticides to control infestations. Insecticidal treatments are most effective if you spray plants late in the summer before the nymphs develop a protective wax coating.