A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

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

pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...

s, 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 continental mainland. It comprises England, Scotland, Wales and North ...

during the

Malayan Emergency The Malayan Emergency, also known as the Anti–British National Liberation War was a guerrilla war fought in British Malaya between communist pro-independence fighters of the Malayan National Liberation Army (MNLA) and the military forces o ...

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 territorie ...

in the

Vietnam War The Vietnam War (also known by #Names, 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 Vie ...

. 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

herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...

s 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 opposin ...

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 perce ...

, 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 Thidiazuron (TDZ) is a plant growth regulator. Applications Plant growth regulator The synthesis routes and their use as plant growth regulating agent were patented in the early 1980s by the German company Schering AG. Thidiazuron is taken up by ...

. 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 com ...

National Agricultural Statistics Service The National Agricultural Statistics Service (NASS) is the statistical branch of the U.S. Department of Agriculture and a principal agency of the U.S. Federal Statistical System. NASS has 12 regional offices throughout the United States and Puer ...

(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 The Rainbow Herbicides are a group of tactical-use chemicals used by the United States military in Southeast Asia during the Vietnam War. Success with Project AGILE field tests with herbicides in South Vietnam in 1961 and inspiration by the Briti ...

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 executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...

(U.S. EPA) concluded that the use of agricultural defoliants led to increased risks of water contamination and dangers to freshwater and

marine life Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...

. 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 substan ...

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 Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...

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 Agent Orange is a chemical herbicide and defoliant, one of the "tactical use" Rainbow Herbicides. It was used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. It ...

, a defoliant used by the

during the

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 Dioxin may refer to: * 1,2-Dioxin or 1,4-Dioxin, two unsaturated heterocyclic 6-membered rings where two carbon atoms have been replaced by oxygen atoms, giving the molecular formula C4H4O2 *Dibenzo-1,4-dioxin, the parent compound also known as ...

contaminants. Members of the Air Force Ranch Hand and the

Army Chemical Corps The Chemical Corps is the branch of the United States Army tasked with defending against chemical, biological, radiological, and nuclear (CBRN) weapons. The Chemical Warfare Service was established on 28 June 1918, combining activities that unti ...

who served in the

were occupationally exposed to

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 Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

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 The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is a teaching, research and Extension scientific organization focused on agriculture and natural resources. It is a partnership of federal, state, and county governmen ...

, 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