Paraquat is classified as a viologen, a family of redox-active heterocycles of similar structure. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic to human beings and animals. It is linked to development of Parkinson's disease. The name is derived from the para positions of the quaternary nitrogens. Paraquat is classified as non-selective contact herbicide. Paraquat kills a wide range of annual grasses and broad-leaved weeds and the tips of established perennial weeds. Paraquat is an oxidant that interferes with electron transfer, a process that is common to all life. Paraquat is often used in science to catalyze the formation of reactive oxygen species (ROS), more specifically, the superoxide free radical. Paraquat will undergo redox cycling in vivo, being reduced by an electron donor such as NADPH, before being oxidized by an electron receptor such as dioxygen to produce superoxide, a major ROS. Paraquat is used to control broad-leaved weeds and grasses, being less effective on deep rooted plants such as dandelions. It does not harm mature bark, and is thus widely used for weed control in fruit orchards and plantation crops, including coffee, cocoa, coconut, oil palms, rubber, bananas, vines, olives and tea, ornamental trees and shrubs and in forestry. Other uses include weed control in alfalfa, onion, leeks, sugar beet, asparagus. Paraquat is used for weed control on non-crop land and can be used as a defoliant for cotton and hops before harvesting. Paraquat is used as a desiccant for pineapples, sugar cane, soya beans and sunflower.
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