Magnolia – False Oleander Scale
Q: Any idea what these are on my magnolia leaves and what to do about them?
A: You have false oleander scale. False oleander scale is not a good name since this insect attacks over 100 plant species, including Southern magnolia, sweetbay magnolia, aucuba, and English ivy, as well as oleander.
Armored scales like this are very difficult to control when mature. Horticultural oils are often effective and relatively safe on beneficial organisms. For established infestations, apply a second application in two weeks. Time sprays to coincide with the crawler stage (May-June), which is most susceptible to insecticides.
For tall trees that cannot be sprayed easily, you can use a systemic insecticides that are applied to the root system of the tree. It’s easy to find imidacloprid, sold as as Bayer Advanced Tree and Shrub Insect Control.
A second option is the insecticide dinotefuran, sold as Safari.
Dinotefuran will provide a much quicker kill than imidacloprid.