Mesotrione is a new herbicide being developed for the selective pre- and post-emergence control of a wide range of broad-leaved and grass weeds in maize (Zea mays). It is a member of the benzoylcyclohexane-1,3-dione family of herbicides, which are chemically derived from a natural phytotoxin obtained from the Californian bottlebrush plant, Callistemon citrinus. The compound acts by competitive inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), a component of the biochemical pathway that converts tyrosine to plastoquinone and alpha-tocopherol. Mesotrione is an extremely potent inhibitor of HPPD from Arabidopsis thaliana, with a Ki value of c 6-18 pM. Commercialization of mesotrione began with its launch in the United States, Germany and Austria in 2001. It is now available under various Syngenta trade names — Callisto, Lumax, Lexar, Halex GT, Camix, Calcris, Elumis, Calaris Callisto Xtra and Tenacity — in more than 50 countries, including Austria, Argentina, Belgium, Brazil, Bulgaria, Canada, China, Croatia, Czech Republic, France, Germany, Greece, Hungary, Ireland, Italy, Japan, Netherlands, New Zealand, Mozambique, Poland, Portugal, Romania, Russia, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, Turkey, the United Kingdom and the United States.