Mesotrione is the ISO common name for an organic compound that is used as a selective herbicide, especially in maize. A synthetic inspired by the natural substance leptospermone, it inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) and is sold under brand names including Callisto and Tenacity. It was first marketed by Syngenta in 2001. History The invention of the triketone class of herbicides had its beginnings in an observation in 1977 of allelopathic weed control near a bottlebrush tree, Callistemon citrinus. Chemists at the Stauffer Chemical Company identified the compound responsible as leptospermone, a known natural product which had not previously been reported as having biological activity. Extensive work on analogues led to the discovery and development of sulcotrione and mesotrione. The triketone herbicides were found to be effective on a wide range of commercially-important weed species and to have both pre- and post-emergence activity. Mesotrione was chosen for development (by Zeneca Agrochemicals under the code number ZA1296) because it controls a wide range of broad-leaved weeds...