Scale

Unlike most insects, scale insects are relatively immobile as adults.

Scale insects suck sap from many perennial plants using piercing, straw-like mouthparts. The majority of scale insects are classified as either ‘soft’ or ‘armored’.

Armored scale

Scale insect identification 

There are dozens of scale insect species. They can be found in a variety of sizes, shapes and colors. Generally, however, females and nymphs live under a circular shell, or scale. They have no discernible head or appendages. Adult males are almost never seen, being tiny winged insects. Some scale species have only females that can reproduce without mating. Most armored scale insects (Diaspididae) feature a 1/8” flattened cover with concentric rings and a slight nipple-shaped center. If the cover is removed, the animal will remain on the plant. Euonymus, oystershell, cycad, and San Jose are common armored scale species. Soft scale (Coccidae) insects can grow to 1/4” and they have a humped, waxy surface that cannot be removed. Soft scales feed on phloem sap. Common species include Kuna, Lecanium, Tuliptree, black and brown soft scale.

Identifying scale damage

Scale insects often go unnoticed until the damage is extensive. In some cases, scale insects can practically cover a plant without causing ill effects. Normally, plants infested with scale appear water-stressed because the pests are draining the plants of their bodily fluids. Chlorosis (yellowing) may also occur. Some varieties of scale produce honeydew that attract ants and provide habitat for sooty mold. Armored scale species do not secrete honeydew. 

How to control scale infestations

Control measures depend on the type of scale insect, as well as environmental conditions and the overall health of the plant. In some cases, no treatment is needed. Sago palm and other cycads, however, can be infested with the cycad scale, which can kill mature plants. Applying fixed copper combined with horticultural oil when the plants are dormant or when these pests are in the crawler stage (late winter to early summer) can help control scale insects.

​There are many natural enemies that help control scale, as long as broad-spectrum pesticides are not used. Inspect infested areas to see if the scales are being parasitized. If a small hole can be seen in the shell of a dead scale, it has been killed by a parasitic wasp and treatment is probably not needed. Applying sticky barriers around the trunks of heavily infested trees and shrubs can stop ants from protecting soft scale insects from their predators.​