The established criteria for determining the course of action and corresponding treatment to be taken are:
Tolerance threshold. A visual analysis determines how badly a pest has affected trees and the control method to be applied. This may involve its removal or complete eradication, or its containment by keeping its population at tolerance levels.
Tree placement. The places where trees are planted have a direct influence on how much a pest may affect the general public. Trees on busy squares and streets may have more of an impact on or cause greater nuisance to local residents and economic activity in the surrounding area.
Impact of a pest on a tree's structure. Certain pests can end up affecting the actual structure and stability of certain species. This is the case with pests that affect oak, cypress and palm trees. Timely action can prevent possible subsequent effects that may require the replacement of infected trees.
Effects from quarantine pests. According to the Government's FAO glossary of plant health terms, a quarantine pest can have a potentially serious economic effect on an area in danger even where the pest is not present or has not spread to but is not under official control.
Quarantine pests in Barcelona are considered to be those caused by fire blight and citrus woodlice. European and national regulations establish that the competent bodies have to monitor and control these poisonous organisms, placing great importance on the need to detect blight at the first signs using quick intervention and control to prevent it from developing and spreading in other areas and to know the evolution of already developed blights to stop them growing.