Herbicide
Type of chemical used to kill unwanted plants / From Wikipedia, the free encyclopedia
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Herbicides (US: /ˈɜːrbɪsaɪdz/, UK: /ˈhɜːr-/), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.[1] Selective herbicides control specific weed species while leaving the desired crop relatively unharmed, while non-selective herbicides (sometimes called "total weed killers") kill plants indiscriminately.[2] The combined effects of herbicides, nitrogen fertilizer, and improved cultivars has increased yields (per acre) of major crops by 3x to 6x from 1900 to 2000.[3]
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Sprayed_weeds.jpg/640px-Sprayed_weeds.jpg)
In the United States in 2012, about 91% of all herbicide usage, determined by weight applied, was in agriculture.[4]: 12 In 2012, world pesticide expenditures totaled nearly $24.7 billion; herbicides were about 44% of those sales and constituted the biggest portion, followed by insecticides, fungicides, and fumigants.[4]: 5 Herbicide is also used in forestry,[5] where certain formulations have been found to suppress hardwood varieties in favor of conifers after clearcutting,[6] as well as pasture systems.