A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the development of other herbicides and pesticides, allowed for the

Green Revolution The Green Revolution, also known as the Third Agricultural Revolution, was a period of technology transfer initiatives that saw greatly increased crop yields and agricultural production. These changes in agriculture began in developed countrie ...

, an increase in agricultural production in mid-20th century. Defoliants have also been used in warfare as a means to deprive an enemy of food crops and/or hiding cover, most notably by the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

during the Malayan Emergency and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

in the

Vietnam War The Vietnam War (also known by other names) was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vietnam a ...

. Defoliants were also used by Indonesian forces in various internal security operations.

Use and application

A primary application of defoliants is the selective killing of plants. Two of the oldest chemical herbicides used as defoliants are 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T). 2,4-D and 2,4,5-T are absorbed by broad-leafed plants, killing them by causing excessive hormonal growth. These

phenoxy herbicide Phenoxy herbicides (or "phenoxies") are two families of chemicals that have been developed as commercially important herbicides, widely used in agriculture. They share the part structure of phenoxyacetic acid. Auxins The first group to be discover ...

s were designed to selectively kill weeds and unwanted plants in croplands. They were first introduced at the beginning of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

and became widespread in use in agriculture following the end of the War. Defoliants have a practical use in the harvesting of certain crops, particularly

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...

, in the

as well as a number of other cotton-producing countries. The use of defoliants aids in the effective harvesting of cotton and finer lint quality. The effectiveness of defoliant use in cotton harvesting depends on the type of defoliant(s) used, the number of applications, the amount applied, and environmental variables. Common harvest-aiding chemical defoliants include tribufos, dimethipin, and thidiazuron. According to a 1998 report by the

U.S. Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...

National Agricultural Statistics Service (NASS), tribufos and thidiazuron accounted for 60% of crop area that was treated by defoliants during that crop year.

List of defoliants

In Southeast Asia during the Vietnam War, the Rainbow Herbicides were a group of tactical-use chemicals used by the

military.

Health and environmental effects

In 1998, the

U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an Independent agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...

(U.S. EPA) concluded that the use of agricultural defoliants led to increased risks of water contamination and dangers to freshwater and marine life. High doses of tribufos were labeled as a possible

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

and a toxin to freshwater and marine

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. Dimethipin has also been labeled as a possible human carcinogen. A published study in the ''Journal of Agricultural and Food Chemistry'' reported that through successive surface runoff events in defoliated cotton fields, defoliant concentrations decreased exponentially within the test area and could negatively affect marine life in the runoff zones. Agent Orange, a defoliant used by the

during the Malayan Emergency in the 1950s and the

during the

to defoliate regions of Vietnam from 1961 to 1971, has been linked to several long-term health issues. Agent Orange contains a mixture of 2,4-D and 2,4,5-T as well as dioxin contaminants. Members of the Air Force Ranch Hand and the Army Chemical Corps who served in the

were occupationally exposed to Agent Orange have a higher incidence of diabetes, heart disease, hypertension, and chronic respiratory diseases. Among other occupations, farmers are at a significantly higher risk of developing Alzheimer's disease due to a greater chance of defoliant exposure.

References

External links

Defoliants and Desiccants
by Frederick M Fishel, Pesticide Information Office, Institute of Food and Agricultural Sciences, University of Florida {{Authority control Environmental science Environmental chemistry Soil science Herbicides Pesticides

Use and application

List of defoliants

Health and environmental effects

See also

References

External links