Economic Importance Economic Importance Scale insects are serious plant pests and as small, highly cryptic components of the plant ecosystem, they frequently are not detected until they have caused significant damage. They are particularly difficult to detect in quarantine inspections especially at low population levels. They are most important as agricultural pest of perennial plants and can cause serious damage to nut and fruit trees, woody ornamentals, forest vegetation, greenhouse plants, and house plants. Damage is usually caused by removal of plant sap, but also may be caused by plant pathogens, toxins and the production of large quantities of honeydew with resultant growth of sooty mold fungi that cover leaf surfaces and reduce photosynthesis.
Scales also can be beneficial.
Cochineal scales and mealybugs have been used in the control of noxious weeds.