Scale Insects- Bumps on tree twigs
Scales refers to a large group of insects that feed from the fluids of trees and other plants. They can be divided into two different groups: armored scales and soft scales. Armored scales produce a waxy substance that protects their bodies whereas soft scales excrete copious amounts of sugar in the form of honeydew. Long term infestations are very damaging to tree health. Both types are difficult to control without pesticides, but not impossible.
Scales are typically found on the trunks, limbs and smaller twigs of plants. Though, they are also found on the needles of some coniferous plants (Juniper Scale) and leaves of deciduous trees. They look like barnacles, oyster clusters, or small bumps on trees and are usually found in great numbers. When rubbed with the hand they will smear and “bleed”. A black chalky substance called Sooty Mold is often found where soft scales exist. Sooty Mold grows on the sticky excretion released from the scale that covers any surface below (notice the black sooty mold covering the base of the needles in the photos to the right, click to enlarge). It will appear as a shadow and generally covers the entire area directly under the canopy of the tree.
The life cycle varies between species of scale. Some scales overwinter as immature crawlers in the cracks and crevices of bark while other species overwinter under the protection of their “shell” or in the egg stage. Typically, they become active in the spring and begin feeding and creating eggs. Immature crawlers and mature adults feed on trees by piercing and sucking through the epidermis and extracting nutrients.
Common effects of severe infestations include twig and branch dieback and epicormic sprouting (sucker growth).
There are some effective systemic treatments that deliver a lethal dose of insecticide to the site where scales are feeding. Scales are also quite vulnerable to various insecticide sprays during the young crawler stage.
Dormant Oils reduce populations by killing the insects during the crawler stage and overwintering stage of their life cycle.
Proper watering, annual soil treatments, and power washing or otherwise physically removing them from the plant can help reduce populations.