Black scale usually has one generation per year in interior valley olive-growing districts. In cooler, coastal regions multiple generations occur. Black scale prefers dense, unpruned portions of trees. Open, airy trees rarely support populations of black scale. At first, affected trees and leaves glisten and then become sooty and black in appearance as sooty mold fungus grows on the honeydew.
Infestations reduce vigor and productivity of the tree.
Continued feeding reduces bloom the following year. Olive pickers are reluctant to pick olive fruits covered with honeydew and sooty mold. These parasites, combined with proper pruning, provide sufficient control in northern and coastal orchards. In other regions, biological control is often ineffective because black scale's development pattern hampers parasite establishment. The first indication of black scale is usually the presence of honeydew on the leaves.