Found in practically every part of the country, scales are sucking insects closely related to mealybugs and aphids. Like mealybugs, they have a protective waxy, shell-like coating--but while mealybugs are mobile (albeit slow moving), scales are stationary for almost their entire lives (juvenile scales do move about, but they soon settle down in one spot). They look like small brown or black bumps on branches and leaves; some excrete honeydew, which attracts ants and fosters sooty mold.
Afflicted plants lose vigor and wilt; new growth is distorted. Branches and even whole plants may die. If infestation is light, you may be able to control it by picking scales off the plant or scraping them off with a plastic scouring pad. If the plant is deciduous, spray it with horticultural oil in winter to suffocate the pests.
Juvenile scales crawl slowly and are best controlled by natural predators; they can also be blasted off plants with strong jets of water.
Do not use chemical controls unless the plant is very valuable and all else has failed; chemicals kill the pests' natural enemies and may exacerbate scale elsewhere in the garden. Chemical controls for juvenile scales include acephate, carbaryl, diazinon, and malathion.