Weeds controlled with<unk> <unk> s (, ), also commonly known as weedkillers, are substances used to control unwanted plants. Selective<unk> s control specific weed species, while leaving the desired crop relatively unharmed, while non-selective<unk> s (sometimes called total weedkillers in commercial products) can be used to clear waste ground, industrial and construction sites, railways and railway embankments as they kill all plant material with which they come into contact. Apart from selective/non-selective, other important distinctions include persistence (also known as residual action: how long the product stays in place and remains active), means of uptake (whether it is absorbed by above-ground foliage only, through the roots, or by other means), and mechanism of action (how it works). Historically, products such as common salt and other metal salts were used as<unk> s, however these have gradually fallen out of favor and in some countries a number of these are banned due to their persistence in soil, and toxicity and groundwater contamination concerns.<unk> s have also been used in warfare and conflict. Modern<unk> s are often synthetic mimics of natural plant hormones which interfere with growth of the target plants. The term organic<unk>  has come to mean<unk> s intended for organic farming. Some plants also produce their own natural<unk> s, such as the genus Juglans (walnuts), or the tree of heaven; such action of natural<unk> s, and other related chemical interactions, is called allelopathy. Due to<unk>  resistance – a major concern in agriculture – a number of products combine<unk> s with different means of action. Integrated pest management may use<unk> s alongside other pest control methods. In the United States in 2012, about 91% of all<unk>  usage, determined by weight applied, was in agriculture. In 2012, world pesticide expenditures totaled nearly $24.7 billion;<unk> s were about 44% of those sales and constituted the biggest portion, followed by insecticides, fungicides, and fumigants.<unk>  is also used in forestry, where certain formulations have been found to suppress hardwood varieties in favor of conifers after clearcutting, as well as pasture systems, and management of areas set aside as wildlife habitat.
Herbicide
Amebicide
Fungicide
Prebiotic 
Deodorant
Herbal medicine
Insecticide
Pesticide