Scale Insect Management

Identification, Life Cycle, Damage and Management

US National Collection of Scale Insects Photographs Archive, USDA ARS

Scales are sucking insects which feed mainly on perennial plants, trees and shrubs via tiny, straw-like stylets. Scale infestations are easily overlooked due to their abnormal appearance. Adult females and nymphs of most species are circular to oval, wingless and lack a head or other recognizable body parts. In most species adult males are miniscule and rarely seen. There are two common families of scale; armored and soft and many, many species within each.

The family Diaspididae is that of the armored scale (ex. at right) insects. They appear flattened and plate like, growing only up to 1/8 of an inch. The actual body is beneath this plate like cover, which can be removed leaving the body on the plant. Armored scales causing the most damage include cycad scale, euonymus scale, oystershell scale, and San Jose scale. They do not produce honeydew.

University of Florida

Soft scales are in the family Coccidae and have a smooth, cottony or waxy surface (ex. at left). They grow only to ¼ of an inch long at maturity and appear more humped than armored scale insects. They do not have a cover which can be removed; the surface is actually the body wall of the insect. Soft scales feed on sap and excrete honeydew; an infestation may be apparent due to abundant sooty mold. Commonly found soft scales include; black scale, brown soft scale, Kuno scale, lecanium scales, and tuliptree scale. Scales hatch from an egg and go through two nymphal instars (depending on species and gender), which appear vastly different, before reaching maturity. Once mature, females produce eggs which they protect with their bodies. Yellowish-orange “crawlers” emerge from eggs and spend one to two days walking over plant surfaces before settling in to feed. Nymphs may progress to adults while never moving from their initial spot.

University of Maryland

Plants suffering a scale infestation appear water-stressed; leaves will become chlorotic and prematurely drop, portions with heavy infestations may die. Severity and importance of the infestation will depend on the scale species, environmental conditions and affected plant. Some scale populations will increase drastically in warm weather. A few scale insects do not a problem make and in some cases even large populations won’t damage a plant to the point of mortality.

Many scale species will be effectively kept in check by natural predators. Dependent of the degree to which your landscape and plants are affected, proper treatment and care may be warranted. Contact your arborist if you are concerned about scale insects on your landscape.