Cobb County Extension Service
Horticulture

email: uge1067@uga.edu

SCALE:  Armored Scale (Diaspidinae) and Soft Scale (Lecaniinae)

By Louise Weyer

Closely related to aphids, mealybugs and whiteflies, scales are small sucking pests that attack woody ornamental shrubs and trees.  Most are 1/16 to 1/8 inches in diameter.  They can be oval, round or oyster shell shaped, and the color ranges from white to black, but predominately browns and grays.

Armored scales are 1/8 inch long and have a thick hard wax scale covering above the body and a thinner scale beneath the body that closely fits the bark surface of the plant.  Eggs are laid under the protective scale where they winter over.  In the spring the young crawl from beneath the scale and move about for a short time to select a favorable location to feed.  As they start to suck the sap from the plant they secrete fibers of wax to cover their body.  The insects molt very shortly after beginning to feed and shed their legs.  Females will remain at this site while males will develop into small winged insects, which are incapable of feeding.  They die shortly after mating.  The pregnant female increases in size very rapidly, laying 40 – 80 eggs that hatch in 2 – 8 weeks.  The female body then shrinks to the small end of the scale where she finally dies.

An important identifying characteristic is their habit of remaining attached to the host plant.  Slip a knife under the armored scale and you will see the body of the scale like a turtle, its legs and antennae waving about and clearly visible with a hand lens.  Armored scales do not produce much honeydew.

Soft scales are generally larger and darker than armored scales, and their shell does not lift off the body.  A marking in the form of an “H” can be seen on the backs of light colored soft scales.  The insect secretes a tough polysaccharide substance to form a protective shell.  The scales are brown, black or mottled in color.  The young female scales may move about for a time after they begin feeding.  Soft scales retain their legs and antennae through adult life.  Their life cycle is similar to the armored scale.  Soft scales produce much honeydew that attracts ants and provides nutrition for sooty mold.

DAMAGE:  A few scales will not cause significant damage, but will look unsightly.  A plant with a high infestation of scale may turn yellow.  If branches are heavily infested or ringed with scales, they will become cracked and scaly.  The plant will lose its vigor, foliage will be undersized and have yellow specks.  Death of the plant is possible.  Adult scales are very visible.  If in doubt if it is scale or a natural feature, scrap the spot, if you see green tissue beneath, it is part of the plant.  If it is scale you can disturb its cover, and with a hand lens, you will be able to see the sucking mouthparts.  Scale can be spread from plant to plant on the feet of birds and insects.  Scale can be a vector of viruses that cause plant diseases

CONTROL:  Selecting plants not prone to scale infestation is a significant role in managing this problem.  Be sure to inspect plants frequently looking for scale.  Ants are attracted to the honeydew of soft scale.  If you see lady beetles and other beneficial insects associated with scale, this is as clue that closer inspection and possible remedial actions are required. 

During the dormant season, spray the plants with lime-sulfur or insecticidal oils.  In spring and summer when young crawlers are actively moving on the plant, use an insecticide such as Sevin, Malathion, Cyfluthrin, horticultural oil or insecticidal soap.  The application should cover both sides of leaves and all twigs and branches.  Scales are most vulnerable to chemical controls at the crawler stage.  Check the plants for crawlers which look like small and flat pancakes. 

If only a few scale are present, they can be rubbed off with garden gloves, an old toothbrush or an alcohol dipped cotton swab.  This will break their mouthparts and they cannot reinfest the plant.

It is advisable to prune out heavily infested plant parts or discard the plants and replace them.

Several parasitic wasps and lady beetles offer natural control.  Scales can be controlled by moderating the amount of nitrogen in plant fertilizer.  They increase as the nitrogen levels in plants increases; therefore, use just enough nitrogen to keep the plant healthy.

Reference:        Complete Guide to Pest Control, George W. Ware, Thomson Publications

Common Sense Pest Control, William Olkowski, Sheila Daar, Helga Olkowski, TheTaunton Press

Destructive and Useful Insects, C. L. Metcalf, W. P. Flint, R. L. Metcalf, McGraw-Hill Book Co.

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The University of Georgia and Ft. Valley State University, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.