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A herbicide is a pesticide used to kill unwanted plants. Selective herbicides kill certain targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often based on plant hormones. Herbicides used to clear waste ground are nonselective and kill every plant with which they come into contact.

Table of contents
1 History
2 Uses
3 Classification of herbicides
4 Application
5 Terminology
6 Some major herbicides in use today
7 Other herbicides of historical interest
8 External links


The first widely used herbicide was 2,4 dichlorophenoxyacetic acid, often abbreviated 2,4-D. It first saw widespread production and use in the late 1940s. It is easy and inexpensive to manufacture, and kills many broadleaf plants while leaving grasses unaffected. Its low cost has led to continued usage today. Like other acid herbicides, current formulations utilize either an amine salt (usually trimethyl amine) or one of many esters (ester) of the base compound. These are easier to handle than the acid.

There are earlier examples of cultural controls, such as altering soil pH, salinity, or fertility levels to control weeds.

2,4-D exhibits relatively poor selectivity, meaning that it causes stress to non-target plants. It is also less effective against some broadleaf weeds, including sedges and many vinous plants. Many other herbicides have been developed to address these limitations.

The 1970s saw the introduction of atrazine, which has the dubious distinction of being the herbicide of greatest concern for groundwater contamination.

Glyphosate, frequently sold under the brand name Roundup, was introduced in the late 1980s for non-selective weed control. It is now a major herbicide in selective weed control in growing crop plants due to the development of crop plants that are resistant to it. The pairing of the herbicide with the resistant seed led to the consolidation of the seed and chemistry industry in the late 1990s.


Herbicides are widely used in management of landscape turf and in agriculture. They are used in total vegetation control [tvc] programs for maintenance of way for highways and railroads. Relatively smaller quantities are used in forestry, pasture systems, and management of set-aside areas for wildlife habitat.

Classification of herbicides

Herbicides can be grouped by chemical family, mode of action, and type of vegetation controlled.

They are also classified by their activity:


Most herbicides are applied as water-based sprays using ground equipment. Ground equipment varies in design, but the greatest number of acres is sprayed with self-propelled sprayers equipped with a long boom (often 60-80 feet) with flat fan nozzles spaced about every 20". Towed, handheld, and even horse-drawn sprayers are also used.

Herbicides can also be applied aerially using helicopters or airplanes, and can be applied through irrigation systems (chemigation).


Some major herbicides in use today

Other herbicides of historical interest

2,4,5-T was withdrawn from use in the USA 1983, at a time of heightened public sensitivity about chemical hazards in the environment. Public concern about dioxins was high, and production and use of other (non-herbicide) chemicals potentially containing TCDD contamination was also withdrawn. These included pentachlorophenol (a wood preservative) and PCBs (mainly used as a stabilizing agent in transformer oil).

Some feel that the 2,4,5-T withdrawal was not based on sound science. 2,4,5-T has largely been replaced by dicamba and triclopyr.

See also; Weed control, weed, farming, agriculture, FIFRA- Federal insecticide, fungicide, and rodenticide act (USA) (also covers herbicides despite the title), Organic farming, Organic gardening

External links

Manufacturers and distributors

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