Crusty, waxy, or scaly bumps cover stems or leaves. They''re brown, yellow, or white, and can be scraped or picked off. Leaves turn yellow and may drop. In some cases, a shiny or sticky substance coats the leaves. A black sooty mold often grows on the sticky substance.
An uncontrolled infestation of scales may kill the plant after 2 or 3 seasons. Spray with an insecticide labeled for these pests, following label directions.