Topramezone is a pyrazolone herbicide developed by BASF, which is also an HPPD inhibitor, being effective for the control of weeds, which are resistant to glyphosate, triazines, ALS inhibitors and the ACCase inhibitors. Topramezone has a good control efficacy for corn grassy weed and broad-leaf grass worldwide. Topramezone was registered for the first time in Canada in 2006 for application to post-emergence weed removal in cornfield, followed by releases to Latin America, North America, Japan and Germany. In 2009, BASF brought to the Chinese market its Topramezone with the trade name Arietta®. Topramezone is moderately toxic to birds, honey bees, earthworms, fish and aquatic invertebrates. Topramezone strongly inhibited 4-HPPD activity in vitro, with I(50) values of 15 and 23 nM for the enzyme isolated from S. faberi and recombinant enzyme of Arabidopsis thaliana L. respectively.