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Defoliation

DEFOLIATION

DEFOLIATION. Defoliation involves the extermination of plant life that in military operations might conceal enemy armed forces, command centers, supply depots, or, less commonly, fields of crops. Such destruction is accomplished by three principal courses of action: setting fires; dropping napalm or phosphorus bombs; and spraying chemical agents from trucks, helicopters, or fixed-wing aircraft. During World War II and the Korean War the United States employed the former two methods, whereas during the Vietnam War chemical agents, chiefly Agent Orange, tended to be used. Defoliation generally produced the desired military objectives, but the human and ecological consequences remain controversial.

In Vietnam the American attempt to defoliate jungle growth and thus expose the enemy focused on the areas around South Vietnamese and later American base camps; along the Ho Chi Minh Trail; across the Demilitarized Zone separating Northand South Vietnam; up and down rivers, canals, and railways; and on any suspected North Vietnamese or Vietcong concentration. In a July 1999 interview Elmo R. Zumwalt Jr., the commander of naval forces in Vietnam from 1968 to 1970, explained that he had ordered the use of defoliants because his personnel were taking casualties at the rate of 6 percent a month, which meant the average young man would have about a 70 percent probability of being killed or wounded during his year's tour.

The campaign to reduce that casualty figure was designated Operation Ranch Hand, which began officially in January 1962 and lasted until January 1971. During that period U.S. Air Force UC-123 aircraft flew thousands of sorties and sprayed nearly 10,000 square miles with roughly 19 million gallons of herbicide, about 11 million of which were Agent Orange. The nonscientific names for the herbicides—Agent Orange, Agent White, and so forth—were derived from the color codes on the drums that contained the defoliants. These chemicals, mainly those tagged 2, 4-D and 2, 4, 5-T, were combined and sprayed to fatally accelerate plant growth, causing destruction within days of the spraying.

From the outset the military use of herbicides generated negative responses from both Vietnamese and Americans, most particularly when crop destruction was involved. Although the spraying of crops succeeded in reducing the available food supply for the North Vietnamese and Vietcong, it also resulted in the destruction of innocent farmers' crops. State Department officials argued that what little advantage was gained in diminishing the enemy's food supply was vastly exceeded by the ill will generated from the unavoidable damage to non-enemy crops. Since crop destruction never constituted more than 15 percent of Ranch Hand's operations, defoliation advocates in the Defense Department grudgingly accepted sporadic political restrictions placed on crop eradication activities, down to the ending of all chemical operations in January 1971.

Other consequences—chiefly political, ecological, and medical—ensued. During the war many in the American media and scientific communities claimed that the use of herbicides constituted chemical warfare, outlawed by numerous treaties to which the United States was a signatory. At the very least this charge created a public relations problem and added to the opposition that the Vietnam War was generating. It also led to pointed questions about the ecological and human costs of defoliation, compelling the Defense Department to commission studies, the results of which caused further heated debates. One study, begun by the National Academy of Sciences in 1970, asserted in its 1974 report that no long-term damage, including birth defects or environmental degradation, could be attributed to the various herbicidal agents sprayed in Vietnam.

In the 1990s that same organization found connections between herbicides containing dioxin and several ailments, including sarcomas, non-Hodgkin's lymphoma, Hodgkin's disease, and chloracne. Congress, the Air Force, and the Veterans Administration (VA) commenced studies of Vietnam veterans who had possibly been exposed to herbicides. In 1978 the VA began conducting physical examinations, doing laboratory work, and launching a registry to study systematically the latent effects of exposure.

Perhaps the most notable case of an American soldier's illness being attributed to Agent Orange is that of Elmo R. Zumwalt III. His sickness and eventual death from cancer at age forty-two in 1988 attracted much attention, since his father had ordered the spraying of herbicides in areas where the son served from 1969 to 1970. Although a causal relationship could not be established, Elmo III believed one existed, particularly since his son, Elmo IV, had been diagnosed with a genetic disorder. In 2001 a University of Texas researcher, Arnold J. Schecter, produced a public health report on Bien Hoa, where seven thousand gallons of Agent Orange had spilled in 1970. His study revealed high levels of dioxin in children born after the war and in adults who moved to the city from locations where no herbicides containing dioxin were sprayed. Schecter concluded that the toxic substance migrated from soil to the groundwater to waterways, from which fish were caught and eaten. One gathers that some relationship exists between exposure to the various herbicidal agents and numerous health problems, since the VA has provided compensation to nearly two thousand veterans and because the various chemical companies that manufactured the agents settled a class-action lawsuit out of court that provided almost $200 million in damages to veterans.

BIBLIOGRAPHY

Buckingham, William A., Jr. Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia, 1961–1971. Washington, D.C.: Office of Air Force History, United States Air Force, 1982.

Schuck, Peter H. Agent Orange on Trial: Mass Toxic Disasters in the Courts. Cambridge, Mass.: Harvard University Press, 1986.

Texas Technical University. "Vietnam Archive." Burch and Pike collections. Available from http://archive.vietnam.ttu.edu/vietnamarchive.

Wilcox, Fred A. Waiting for an Army to Die: The Tragedy of Agent Orange. New York: Random House, 1983.

Zumwalt, Elmo R., Jr., and Elmo R. Zumwalt III. My Father, My Son. New York: Macmillan, 1986.

ThomasReins

See alsoInsecticides and Herbicides ; Vietnam War .

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defoliation

defoliation The process of leaves being removed from a plant.

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defoliation

defoliation The process of leaves being removed from a plant.

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Defoliation

Defoliation


Several factors can cause a plant to lose its leaves and become defoliated. Defoliation is a natural and regular occurrence in the case of deciduous trees and shrubs that drop their leaves each year with the approach of winter. This process is aided by an abscission layer that develops at the base of the leaf petiole, weakens the attachment to the plant, and eventually causes the leaf to drop. Severe drought may also cause leaves to wilt, dry and drop from a plant. The result of severe dehydration is usually lethal for herbaceous plants, although some woody species may survive an episode of drying. Heavy infestation by leaf-eating insects can lead to partial, or complete defoliation. The gypsy moth (Porthetria dispar ) is an important defoliator that attacks many trees, defoliating, and weakening, or killing them. Parasitic wasps that feed on the larvae can help to control gypsy moth outbreaks. Insecticide sprays have also be used to kill the larvae. Spider mites, any of the plant-feeding mites of the family Tetranychidae (subclass Acari), feed on house plants and the foliage and fruit of orchard trees. Heavy infestation can lead to serious or complete defoliation. Spider mites are controlled with pesticides, although growing resistance to chemical control agents has made this more difficult, and alternative control measures are under investigation.

Along with natural causes of defoliation, chemicals can cause plants to drop their leaves. The best known and most widely used chemical defoliators are 2,4,5 trichlorophenoxyacetic acid (2,4,5-T ) and 2,4 dichlorophenoxyacetic acid (2,4-D ). Both chemicals are especially toxic to broad-leaf plants. The herbicide 2,4-D is widely used in lawn care products to rid lawns of dandelions, clover, and other broad-leaf plants that interfere with robust turf development. At appropriate application rates, it selectively kills broad-leaf herbaceous plants, and has little effect on narrow-leaf grasses. The uses of 2,4,5-T are similar, although it has been more widely used against woody species.

A mixture of 2,4-D and 2,4,5-T, in a product called Agent Orange has been extensively used to control the growth and spread of woody trees and shrubs in sites earmarked for industrial or commercial development. Agent Orange saw extensive use by American forces in Southeast Asia during the Vietnam war, where it was used initially to clear for power lines, roads, railroads, and other lines of communication. Eventually, as the war continued, it was used to spray enemy hiding places, and U.S. military base perimeters to prevent surprise attack. Food crops, especially rice, were also targets for Agent Orange to deprive enemy forces of food. Although Agent Orange and other formulations containing the chlorinated phenoxy acetic acid derivatives are generally lethal to herbaceous plants, woody deciduous plants may survive one or more treatments, depending on the species treated, concentrations used, spacing of applications, and weather. In Vietnam it was found that mangrove forests in the Mekong delta were especially sensitive, and often killed by a single treatment. A member of the dioxin family of chemicals, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been found to be an accidental but common contaminant of 2,4,5-T and Agent Orange. Dioxins are very resistant to attack by microbes in the environment , and are apt to persist in soils for a very long time. Although few disorders have been definitively proven to be caused by dioxins, their effects on laboratory animals have caused some scientists to rank them among the most poisonous substances known. The U.S. government banned some 2,4,5-T containing products in 1979 because of uncertainties regarding its safety, but its use continues in other products.

[Douglas C. Pratt Ph.D. ]


RESOURCES

BOOKS

Addicott, F. T. Abscission. Berkeley: University of California Press, 1952. Gansner, D. A. Defoliation potential of gypsy moth. Radnor, Pa.: U.S. Dept. of Agriculture, Northeastern Forest Experiment Station, 1993.

Teas, H. J. Herbicide toxicity in mangroves. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratory, Springfield Va.: for sale by the National Technical Information Service, 1976.

Whiteside, T. The withering rain; Americas herbicidal folly. New York: Dutton, 1971.

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