Scale insects are small, highly modified animals that have little resemblance to most insects. Because of their small size and often cryptic appearance, large numbers may be present without being noticed. While a few scale insects are little cause for concern, large numbers may be harmful to the host plant. By closely watching your trees and shrubs, we can often catch a scale infestation in its early stages and take appropriate action.
Scale insects injure plants as they feed. Long, threadlike mouthparts are inserted into the host plant and used to suck plant sap from the tissues. If large numbers are present, the insects can remove so many nutrients from the plant that it does not have enough left over to carry on its own metabolic activities.
Scale insects can injure plants in other ways, too. Large amounts of honeydew, a sugary waste product, can cover leaf and other surfaces located beneath a scale infestation. A fungus called “sooty mold” will use the honeydew for food and can cover leaves, sidewalks, patios or other surfaces, giving them a discolored appearance. We divide scale insects into two broad categories: 1) the soft scales, and 2) the armored scales. Each category has characteristics that are important to recognize. Let’s look at each separately.
Categories of Scale Insects
Armored scale insects secrete a thick, waxy covering over the tops of their bodies. This covering, combined with their own cast skins, serves to protect the insect from the environment as well as from contact pesticides. Therefore, it is difficult to control scale insects with most contact insecticides after the waxy covering has formed. Examples of armored scales include pine needle scale, oystershell scale, euonymus scale, and obscure scale.
Soft scale insects do not produce such a thick protective barrier. While they may produce waxy secretions, the wax is granular and does not serve as a protective barrier as do the armored scale secretions. Examples of soft scales insects include lecanium scale, Fletcher scale, cottony maple scale, and magnolia scale.
There are many different scale insects and their life cycles vary. As a general rule, however, armored scales usually spend the winter in the egg stage or as mature females. The eggs are located beneath the waxy scale covers of the female scale insects. The eggs usually begin to hatch during late May or early June.
Read more about scale insect life cycle and management.