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Herbicides are chemicals or biological agents used as pesticides to kill a weed, which is any plant growing where it is not wanted, usually those abundant enough to take over flowerbeds, gardens, or reduce yield in agricultural fields. Reasons for using herbicides include improving the aesthetic appeal of a landscape or ornamental garden, increasing crop yields, or to kill intoxicants or narcotic plants grown as illegal substances. Herbicides have also been used to expose enemy combatants in jungle areas.

Until the time of World War II, weeds were controlled mechanically. This included plowing, weeding by hand, or using a hoe. Cultural controls are methods used to cultivate the land so it is less hospitable to weed development. Altering the pH of the soil, its salinity, and ...

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