Scale

This is a serious infestation! From the photo, it is hard to tell the disease. Golden euonymus (Euonymus japonicusäóÖ Aureomarginatusäó»), the plant affected, is prone to both scale and mildew on a grand scale. If the spots on the leaves rub off, then it is probably scale. Use a cotton swab dipped in alcohol to touch each one. Follow up with a weekly spray of Insecticidal Soap for 3 weeks to break up the life cycles of these piercing and sucking insects. Since so many of your Euonymus leaves were affected, you might be better off removing this shrub and starting over.

Scale insects are mostly immobile, so once removed, it is not likely to move to the other plants. They suck the nutrients out of the leaves and branches, and if untreated, can seriously damage a plant. Many insecticides cannot penetrate the insect’s shell, so you’ll need something specially formulated for scale. We suggest you take a few leaves into a local nursery and explain your problem. They can recommend a horticultural oil or systemic poison formulated for ornamentals. Good luck!