Magnolia scale (Neolecanium cornuparvum)

Published August 01, 2017

Magnolia can usually tolerate small populations of scale, but extensive feeding by a large population will lead to stress and decline of the tree.

Magnolia scale is the largest soft scale insect, reaching ½ inch in length. It attacks magnolia trees and tulip trees. Star magnolia, saucer magnolia and many hybrids are most commonly and severely affected.

Scale insects can be divided into two groups: armored scales and soft scales. Armored scales secrete a protective cover over their bodies and usually overwinter as eggs beneath the female cover. Soft scales are usually larger and lack the protective cover, but protect themselves with waxy secretions. Soft scale produce honeydew; armored scale do not.

Source: The Morton Arboretum. Photos: Brian Kunkel, University of Delaware, Bugwood.org; John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org

THE FACTS ABOUT magnolia scale

LIFE CYCLE

Magnolia scale

This scale spends the winter on small twigs as tiny, dark-colored nymphs. In the spring, the scales begin to feed, mature, and change color. The males, which turn white, are smaller than the females, about 1/8 inch in length, and emerge as tiny, gnat-like insects. The males mate with the females and then die. The females turn white to brownish-purple in color and continue to enlarge through July. Magnolia scale eggs hatch internally and the crawlers emerge from the mother insect. Crawler emergence occurs late summer into early fall.

DAMAGE

Scale insects have sucking mouth parts and feed on sap from the tree. Trees can usually tolerate small populations of scale, but extensive feeding by a larger population will stress the trees and often leads to yellowing of leaves and twig dieback. Over time, an untreated population of magnolia scale may lead to decline of the tree.

CONTROL

Infestation on magnolia

Cultural: Trees that are stressed are more prone to attack by scale. Avoid excessive fertilization as this make lead to a build-up of scale populations.

Physical: It may be possible to manage small populations by pruning.

Chemical: Scale insects are very vulnerable in the crawler stage. Chemical sprays should be used at the time of crawler emergence (on average from late August through the end of September). Insecticidal soaps and horticultural oils can be effective against the crawler stage but usually have no effect on the adult scale. They also have a limited impact on beneficial insects that may attack magnolia scale. These products require multiple applications because they have no residual activity. Apply dormant oil to overwintering nymphs in early spring before buds open. Systemic insecticides that contain imidacloprid or dinotefuran can be drenched into the soil several weeks before the crawlers become active. These products will kill the crawlers but take time to move through the tree, so they must be applied early.

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