Hawthorn (Crataegus)-Scale insect

Several species including
Oystershell scale (Lepidosaphes ulmi)
San Jose scale (Quadraspidiotus perniciosus)

Pest description and damage Scale insects are common on many ornamental trees and shrubs as well as landscape plants. Adult female scale live under a shell-like covering that may resemble a "volcano," "barnacle," "hemispherical bump," "cotton puffs," "oyster" or even flat, soft and naked, and with various dull colors and markings. They are found attached along the branches, twigs, leaves, needles or even fruit. Most scale insects measure from 0.0625 to 0.25 inch in length. Occasionally scale build up large enough numbers to cause damage to the host plant. These insects have piercing-sucking mouthparts that they inject into plant tissues to feed on plant juices. Large populations of scale can devitalize plants and retard growth, as well as discolor the foliage. Severe infestations can kill twigs. In many cases, large quantities of honeydew are produced, which makes leaves and underlying plants shiny and sticky. Sooty mold fungus may grow on the honeydew giving the plants a dirty, sooty appearance.

For biology, life history, monitoring and management

See "Scale insect" in:

Management-chemical control

See Table 1 in: