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herbicide (hrˈbəsīdˌ), chemical compound that kills plants or inhibits their normal growth. A herbicide in a particular formulation and application can be described as selective or nonselective. In agriculture, selective herbicides are often used instead of tillage, or in combination with tillage and other agronomic practices, to control weeds without damaging crops. For these no-till or low-till systems, scientists have used biotechnology to develop crop varieties with increased tolerance for herbicides. Nonselective herbicides (e.g., paraquat) toxic to all plants, are used where complete control of plant growth is required.

Contact herbicides kill only the parts of the plant they touch; systemic herbicides are absorbed by foliage or roots and translocated to other parts of the plant. Preemergence herbicides, mixed into the soil, will kill germinating seeds and small seedlings. Postemergence herbicides either hinder photosynthesis or inhibit growth.

Early chemical herbicides were inorganic compounds. Herbicides such as ashes, common salts, and bittern have been used in agriculture since ancient times. Observation in 1896 that Bordeaux mixture, a fungicide, also provided control of certain weeds, led to the use of copper sulfate as a selective weed killer to control charlock (wild mustard) in cereals. By 1900, solutions of sulfuric acid, iron sulfate, copper nitrate, and ammonium and potassium salts were known to act as selective herbicides; soon thereafter sodium arsenite solutions became the standard herbicides, and they were used in large quantities until about 1960. Other inorganic herbicides include ammonium sulfamate, carbon bisulfide, sodium chlorate, sulfuric acid solutions, and formulations containing borate.

Organic herbicides began to be produced in earnest with dinitrophenol compounds in 1932. A breakthrough occurred in the 1940s with 2,4-D (2,4-dichlorophenoxyacetic acid), a compound similar to plant hormones, which is a highly selective systemic herbicide when used in very small quantities. 2,4-D was quickly adopted to control broad-leaved weeds in corn, sorghum, small grains, and grass pastures, as well as in lawns and other ornamental turf. The phenoxyaliphatic acids and their derivatives, another major group of organic herbicides, succeeded because of their selectivity and ease of translocation. Other groups of organic herbicides include organic arsenicals, substituted amides and ureas, nitrogen heterocyclic acids, phenol derivatives, triazines, and sulfonylureas.

In the 1960s and 1970s, a combination of 2,4-D and 2,4,5-T was widely used in Vietnam as a defoliant under the name Agent Orange. As a result of questions concerning the possible health effects of the use of Agent Orange, heightened awareness of possible ecological and health dangers attributable to herbicides has resulted in reevaluation of many compounds and has called indiscriminate use into question. Use of the dioxin-containing 2,4,5-T was prohibited in the United States in 1984. In 1975, Mexico, at the urging of the United States government, began spraying fields of marijuana with paraquat, which both eliminated the crop and raised fears of toxic side effects in marijuana users.

Glyphosate, a compound first identified as a herbicide in 1970 and sold beginning in the 1970s (initially only under the tradename Roundup), has been widely used as a broad-spectrum weedkiller because of its apparent relatively low toxicity and tendency to degrade relatively quickly in the environment. Beginning in the 1990s, the use of crop strains that were resistant to its herbicidal effects contributed to the herbicide's much more widespread use and led to the development of so-called superweeds, which have resistance to glyphosate.

See also pesticide.

The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.


A chemical agent that destroys or inhibits plant growth.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a chemical that destroys plants, esp one used to control weeds
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
" There is a growing public concern over the continuous usage of glyphosate with local and international agronomists calling for total ban of the weed killer. Several countries in the world have joined the call to ban the use of these herbicides following a wave of lawsuits against Monsanto and parent company Bayer by those diagnosed with cancer after using Roundup in America.
Hardeman's case is one of more than (https://www.ibtimes.com/bayer-lawsuit-german-company-pay-2-billion-couple-after-roundup-cancer-case-2791980) 13,400 plaintiffs that are suing the company over its Roundup weed killer, which they claim is unsafe due to the active ingredient glyphosate, the news outlet reported.
To make an effective batch of weed killer, purchase a gallon of white vinegar from your favorite store.
Wrexham Council is one of many authorities across the UK which deploys a weed killer containing the chemical to control plants.
The past breaches include Neal spraying weed killer, and pouring urine through the fence onto her neighbours' plants.
Weed killer with the ingredient glyphosate can currently be used inCroydonand it has been linked to causing cancer in a landmark case in America.
A recent EPA ruling clears the path for Arkansas farmers to use the herbicide dicamba on soybeans and cotton, ending a state-wide ban on the weed killer's use, according to an Associated Press report.
SAN FRANCISCO -- A Northern California groundskeeper said Wednesday that he will accept a judge's reduced verdict of $78 million against Monsanto after a jury found the company's weed killer caused his cancer.
ASPECIAL Forces veteran, publicly branded a poisoner, has broken his silence to deny he killed his my wife with weed killer.
BEES could be dying as a result of exposure to the world's most popular weed killer, new research suggests.
It is growing soft at the moment so it is best to crunch the foliage to expose a wound and then spray with SBK weed killer which you can find online or at your local garden centre.