A herbicide, commonly known as a weedkiller, is a type of pesticide used to kill unwanted
plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed.
Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of
plant hormones. Herbicides used to clear waste ground,
industrial sites, railways and railway embankments are non-selective and kill all plant
material with which they come into contact. Smaller quantities are used in forestry, pasture
systems, and management of areas set aside as wildlife habitat.
Some plants produce natural herbicides, such as the genus Juglans (walnuts), or the tree of
heaven; such action of natural herbicides, and other related chemical interactions, is
called allelopathy.
