The magnolia scale, Neolecanium cornuparvum (Thro), is one of the largest and most conspicuous scale insects known to occur in Ohio. Adult females may reach nearly ½ inch in diameter when fully grown. The scale is shiny, tan-brown, and smooth. As the scales grow, they are often covered with a white mealy wax. This wax is lost at the time the crawlers emerge. As the name implies, this insect is primarily a pest of various species of magnolia. Saucer, star, lily, and cucumber tree magnolias are the most common trees attacked.

Damage

Magnolia scales have sucking mouthparts and when heavy infestations completely encrust branches, the branches often die. Badly infested branches and twigs are weakened and growth is retarded. Leaves may also be under-developed. Under a continuous and heavy attack, trees may be killed. Like most soft scales, the excess plant sap is excreted as a sweet, sticky material called honeydew. The honeydew drips onto the foliage and branches. A dark fungus, called black sooty mold grows on the honeydew which results in the leaves becoming blackened. This greatly detracts from the plant’s normal ornamental value. The honeydew also attracts ants, bees, wasps, and flies which feed on it.

Description and Life Cycle

The magnolia scale spends the winter on 1 to 2-year-old twigs as tiny, dark-colored nymphs. As temperatures warm in the spring, the scales begin to suck sap and have molted once by early May. At this time, two distinct forms can be found, males and females. The males remain small, about ⅛ inch, and soon turn a translucent white. Soon after the males turn white, they emerge as tiny, pink to yellow gnat- like insects with two long waxy threads extending from the tip of the abdomen. The females continue to expand and by early June, they have turned a brownish-purple color. This is also the time they produce excessive amounts of honeydew. By July, the females are covered with a powdery-white, waxy coating and are turning more of a yellow- tan color. By late July and August, the adult females begin to give birth to their young, known as crawlers. The tiny, mobile crawlers move around until they find a suitable feeding site on which they settle down, feed, and remain through the winter.

Control Hints

Though there are several predators and parasites known to attack this scale, they rarely do an effective job of control, especially on smaller magnolias.