What does scale look like?
There are many species of scale insects that feed on a wide range of host plants. One type of scale (Coccus hesperidum) are adult females that are smooth, oval, brown, flattened, and up to 1/5 inch long. Nymphs are similar, but smaller and almost transparent. Both can be difficult to see on leaf veins and twigs. Adult males are tiny, two-winged insects. Many plants are hosts to this insect. Indoor plants such as citrus, and other tropical and subtropical fruit; also a wide range of foliage plants and greenhouse ornamental plants can be attacked by scale insect as well as outdoor hardy plants. See images below in this link:
Courtesy of the NYBG Plant Information Service