Home & Garden

Learn to spot and control scales on your plants

Scales can weaken plants and stunt their growth.
Scales can weaken plants and stunt their growth.

Scales are sucking insects that insert their tiny, strawlike mouthparts into bark, fruit or leaves of trees, shrubs or other perennial plants.

Scales don’t look like other insects. Adult females usually have a circular to oval shape, are wingless, and lack a head or any easily identifiable body parts. Adult males are rarely seen and are tiny, delicate, whitish insects with one pair of wings and a pair of long antennae. Some species lack males altogether; females reproduce without mating.

The two most common forms of scales are armored scales and soft scales. Armored scales have a flattened, plate-like cover that is less than1/8 inch in diameter. The actual insect body is under neath the cover; if you remove the cover, the insect body will remain on the plant. Soft scales grow up to 1/4 - inch long and have a soft, cottony or waxy surface. At maturity, soft scales are usually larger and more rounded and convex than armored scales. Their surface is the actual body wall of the insect and cannot be removed. Soft scales feed on sap and ex crete abundant, sticky honeydew. This drips on plants and surfaces underneath and promotes the growth of blackish sooty mold.

While most varieties of scales cause minimal damage, some do weaken plants and impact growth. Infested plants look water stressed. Their leaves turn yellow and drop off prematurely. Plant parts that remain heavily infested may die. If the scales produce honeydew, they will attract ants. Ants feed on the honeydew and harvest it, carrying it back to the nest to feed the developing colony.

Scales are usually kept in check by small parasitic wasps and certain predatory beetles, true bugs, lacewings and predatory mites. Ants will fight off these parasites and predators to protect the honeydew producer, so it’s important that they are controlled. Prune up branches that touch the ground or buildings and allow access to the plant. Apply a layer of Tanglefoot to the trunks of trees. (Wrap the trunk with a collar of heavy paper or masking tape first to avoid injury to the bark.)

For more information and photos of scales, visit the UC IPM website http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7408.html#IDENTIFICATION.