Trade between continents, especially trade in plant materials, often involves unintentional imports of pest organisms. Most of the time such transmissions pose no threat, but sometimes organisms can establish themselves in their new environment and cause damage in agriculture and natural habitats. Once an organism has become established, damages may be considerable since the pest is capable of proliferating in the absence of any natural balance. It is therefore reasonable to carry out measures so as to prevent pests from being introduced or at least contain their spreading.
The international community established regulations in order to prevent spreading of agricultural pest organisms as effectively as possible. A list of organisms to be controlled is of primary importance. Since measures to prevent pest spreading involve costs and hamper trade, combating efforts have been limited to the most harmful pests. These are organisms which cause proven damages to agriculture and whose spread may be effectively controlled. They are usually spread by trade operations and not through natural pathways. Organisms which have already widely spread or which are not officially controlled are not listed.
Definition of the FAO of quarantine organisms (QO): A pest of potential economic importance to the area endangered thereby and not yet present there, or present, but not widely distributed and being officially controlled.
How measures against such pests are implemented depends on the size of the area (field, region, part of the country, country, and continent). Initially the definition of QO was related to a particular country. But since Switzerland is associated to the EU in terms of plant protection, the QO list is set up by the EU. This may cause a paradox that a QO might be widely distributed in Switzerland. Switzerland must make sure that a QO cannot infest other European countries which have not yet been affected.
The definition of a QO requires that its infestation be known, i.e. that official monitoring is in place.
The infestation dynamics cause situational changes over space and time so that various time periods or special zones may be identified during which or where official control measures may be implemented:
1) Prevention: The organism is not present in the area yet; measures are limited to imports.
2) Eradication: The organism has been detected locally where it is supposed to be eradicated.
3) Containment: The organism has established itself in an area. Its spread should be slowed down.
4) Suppression: The organism has practically established itself in an entire area. Official measures aim at preventing other areas from becoming infested. Control is no longer officially done, but is in the interests of the local farming communities.
Since QO are often spread by trading plant material, measures targeting propagation materials are of prime importance. Tests must ensure that propagation materials are free of QO at each processing stage. This is not only a reasonable provision for the local environment, but also an essential contribution to prevent pest spreading across larger areas or countries.