Through the international exchange of plants and plant products, many harmful insects and destructive plant diseases have travelled with their hosts to distant lands. Inadequate plant quarantine services have failed to exclude such pests and diseases, many of which have become established with even greater vigour in their new environments.
Prior to 1870 there was little realization by national governments of the dangers inherent in a free exchange of the plants and plant products that are hosts to injurious plant pests. The Colorado potato beetle was responsible for the first legislation affecting the international movement of a plant product, after its introduction into Germany. Following eradication of the infestation, a decree was issued by the German government in 1875, forbidding the further importation of potatoes and potato sacks. In the same year France also imposed exclusion measures against the beetle.
About 1859 the grape fungus Phylloxera, a native of the eastern USA, was introduced into France through the medium of imported grapevine cuttings; during the following 20 years it spread throughout Europe. Within 25 years of its discovery in France it had destroyed nearly one third of the French vineyards. Similar shipments of vine cuttings from France about 1872 spread the Phylloxera to Australia, where legislation to suppress the infestation was passed in 1877. This act gave power to quarantine and even to eradicate vines and destroy vineyards. In France regulation relating to Phylloxera was proclaimed in 1878. The first international action in the field of plant quarantine was in 1881, when a conference held in Bern, Switzerland, drafted an agreement known as the Phylloxera Convention, preventing the introduction of the Phylloxera from the USA and restricting the movement of grapevines and grape products to prevent its further spread between European countries.
Plant pests and diseases destroy over 20% of the potential world harvest annually. Among the hundreds of noxious insects and plant diseases that countries seek to exclude through quarantine regulations and controls are the golden nematode of potatoes and tomatoes, pink bollworm of cotton and cotton boll weevil, harmful species of fruit flies, such as the Mediterranean oriental and Mexican fruit flies and the melon fly, Colorado potato beetle, citrus canker and various virus diseases. Because there is greater impetus behind species introduction, commercial and otherwise, and behind international transport, than there is behind quarantine controls, the execution of controls remains inadequate, and plant pests and diseases are carried to new regions on plant products, seed and nursery stock. The worldwide distribution of many major crop and forest pests – the Hessian fly, Japanese beetle, Colorado potato beetle, grape fungus Phylloxera, spruce sawfly and gypsy moth; tree diseases – Dutch elm disease and chestnut blight; and crop diseases – golden nematode of potatoes, potato blight and vine powdery mildew – testify to the ability of man to spread plant pests and disease.
Quarantines are effective, preventing the introduction of many pests and diseases and retarding the movement of others, giving scientists time to combat such pests and diseases before they become well established; and annually save agriculture large amounts of money, more than sufficient to offset the business and trade losses due to, and the costs of, quarantine control measures.
As man is unable to effectively prevent the movement of microscopic pathogens, many quarantines are scientifically unsound and ineffectual. Occasionally, quarantines have been used as economic sanctions in restraint of free trade and have caused unnecessary economic losses.