p-Hydroxyphenyl pyruvate dioxygenase inhibitor, which ultimately affects carotenoid biosynthesis. Selectivity in maize derives from differential metabolism (to the 4-hydroxy derivative) and also possibly from slower foliar uptake. Mode of action Uptake is foliar and via the root, with both acropetal and basipetal translocation. Symptoms are whitening of leaves, followed by necrosis of the meristematic tissue. Uses Under development for pre-emergence (at 100-225 g/ha) and post-emergence (at 70-150 g/ha) control of broad-leaved weeds, such as Xanthium strumarium, Ambrosia trifida, Abutilon theophrasti, and Chenopodium, Amaranthus and Polygonum spp., and some grass weeds, in maize.