Description
Soft scales are serious pests of hundreds of woody plants, appearing as crusty bumps on bark and leaves. This scale group contains some of the largest species of scales found in the United States. Soft scales (also see Cottonycushion Scales) are related to both mealybugs (see Mealybugs) and armored scales (see Armored Scales). Many soft scales look like mealybugs; they are covered with a white, powdery wax during part of their life. Like mealybugs, soft scales excrete large quantities of undigested sap, called honeydew, as they feed on plant tissue. Soft scales develop an external skeleton that looks like the armored scales' shell-like covering. This skeleton can't be removed without killing the insect. Depending on the species, female scales lay eggs or produce living young beneath their bodies. The egg-laying females die and shrivel, and the skeletons protect the eggs until they hatch. The young scales, called crawlers, move away from their protected sites to find a suitable spot to feed. This stage of the insect, when it is not protected by a skeleton, is most susceptible to insecticides.
Control
Control is often aimed at the susceptible crawler stage, whose seasonal appearance varies with each species. Spray crawlers on ornamentals with an insecticide containing acephate. Contact your local County Extension Agent (see County Extension Agents) for the best time to spray for scales in your area. Control scales on fruit trees with an insecticide containing diazinon or malathion. A horticultural oil spray is very effective against the eggs and often against the crawlers.
