Defoliation, a form of chemical warfare, is the use of herbicides to destroy plant or forest landcover in order to improve visibility and cut off food supplies to the enemy. The use of chemical herbicides cannot be limited to affecting only the enemy, however. It both drifts over borders into neutral neighbouring areas and countries and also affects innocent civilians and animals in the warring countries themselves. Chemical agents have been proved to produce birth defects in humans and animals; have caused the starvation of civilians due to the destruction of food crops (sometimes so completely as to render regeneration impossible); have caused the death - and possible extinction - of species of animals which depend on foliage for food and concealment; and leave toxic residual in humans and animals which can eventually accumulate to lethal levels.
In the Vietnam War, the USA used considerable amounts of herbicides against Vietnam; in 1967, 50 million lbs of herbicides were sprayed over 1 million acres of South Vietnam; in 1968 10 million gallons infected 4 million acres (one third of which was crop land); usage was discontinued in 1970. A 1971 report shows that by 1970, 1.2 million acres of mangrove forests in Vietnam had been totally destroyed and 600,000 people had been cut off from their food supplies. Records from a Saigon children's hospital indicate a dramatic increase (from 26 per 1000 to 64 per 1000) in cleft palate, spina bifida, and other birth defects after 1966, the year in which heavy antiplant spraying began. In 1984, Kampuchea complained to the United Nations Commission on Human Rights that the Vietnamese occupying forces in Kampuchea were using chemical weapons in water sources and food supplies, leading to severe diarrhoea, dysentery, fever, and possible death.
The use of defoliants is even more inhumane than traditional warfare because of its unobservable and thus undetectable presence. It kills civilians as well as combatants and the consequences of its resultant ecological calamity remain long after the combat ceases.
Defoliants have been proved to be highly effective. They can kill personnel without great material destruction and the weapons used are relatively inexpensive. They are particularly useful in combating guerrilla warfare by exposing enemy positions usually concealed in foliage, thus making defensive positions possible. The use of defoliants on North Vietnamese supply routes was shown to have seriously impeded North Vietnamese movements.