Magnolia scale is the largest scale found in North America. The scale is often the size of a fingernail. A major pest on magnolias in the eastern states; it has become a pest in Illinois since the mid-nineties.
This scale produces honeydew in large quantities. Sooty mold (a fungus) grows on the honeydew. This causes the plant to turn blackish in appearance. In addition to the feeding damage by the scale, the sooty mold, when it becomes dense enough, causes the leaves to die early.
The scale will over winter as a first-instar nymph (look like immature adults). The nymphs continue to develop the following spring. The nymphs secrete a powdery white wax over their body. In northern Illinois, the adult female produces live young.
In the first nymph stage is when the scale is most susceptible to control. This occurs in late September to early October in Northern Illinois. Or treat in the spring when buds are opening. Insecticides need to be applied when insect is in the crawler stage.