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

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

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 used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all p ...

s, allowed for the

Green Revolution The Green Revolution, or the Third Agricultural Revolution, was a period during which technology transfer initiatives resulted in a significant increase in crop yields. These changes in agriculture initially emerged in Developed country , devel ...

, 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 Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

during the

Malayan Emergency The Malayan Emergency, also known as the Anti–British National Liberation War, was a guerrilla warfare, guerrilla war fought in Federation of Malaya, Malaya between communist pro-independence fighters of the Malayan National Liberation Arm ...

and the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

in the

Vietnam War The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam w ...

. 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 weed killers, 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 f ...

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 discove ...

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 (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

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 (), first recorded in ancient India, 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 ...

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

Examples of defoliants

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

military. The environmental destruction caused by this defoliation has been described by Swedish Prime Minister

Olof Palme Sven Olof Joachim Palme (; ; 30 January 1927 – 28 February 1986) was a Swedish politician and statesman who served as Prime Minister of Sweden from 1969 to 1976 and 1982 to 1986. Palme led the Swedish Social Democratic Party from 1969 until as ...

, lawyers, historians and other academics as an

ecocide Ecocide (from Greek 'home' and Latin 'to kill') is the destruction of the natural environment, environment by humans. Ecocide threatens all human populations that are dependent on natural resources for maintaining Ecosystem, ecosystems and ensu ...

Health and environmental effects

In 1998, the U.S. Environmental Protection Agency (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 collective ecological communities that encompass all aquatic animals, aquatic plant, plants, algae, marine fungi, fungi, marine protists, protists, single-celled marine microorganisms, microorganisms ...

. High doses of tribufos were labeled as a possible

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

and a toxin to freshwater and marine

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

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 or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to ''channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

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 uses of 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 1962 to 1971. T ...

, 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 contaminants. Members of the Air Force Ranch Hand and the Army Chemical Corps 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 neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

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 An institute is an organizational body created for a certain purpose. They are often research organisations (research institutes) created to do research on specific topics, or can also be a professional body. In some countries, institutes ca ...

, University of Florida {{Authority control Environmental science Environmental chemistry Soil science Herbicides Pesticides

Use and application

Examples of defoliants

Health and environmental effects

See also

References

External links