Pyrithiobac sodium (also known as PE350) is a carboxyphenylthiodimethoxypyrimidine derivative patented by Kumiai Chemical Industry Co., Ltd. and Ihara Chemical Industry Co., Ltd. as herbicide and commercialized for uses in cotton cultivation. Pyrithiobac acts as a potent inhibitor of Acetohydroxyacid synthase (AHAS), also known as acetolactate synthase, that catalyzes the first reaction in the pathway for synthesis of the branched-chain amino acids. Pyrithiobac is applied POST at 70 g/ha in cotton (1- to 2-leaf stage) for effective control of several broadleaf weeds such as Xatithium stmmarium, Ipomoea spp., Abutilon theophrasli, Sesbania exaltata (hemp sesbania), Salvia reflexa, Sida spinosa, Amaranthus spp., etc. When applied at this rate, wheat, soybean and grain sorghum may be rotated with cotton with no crop toxicity to these crops. Cotton is very tolerant of Pyrithiobac even at rates as high as 112 g/ha. It may also be applied PPI or PRE in cotton to control Cassia occidentalis, a troublesome broadleaf weed. Higher rates cause injury to cotton. However, caution may need to be exercised, as insecticides (malathion, fenvalerate, methomyl, chlorpyriphos, etc.) applied along with Pyrithiobac, as mixtures are likely to make cotton sensitive to the herbicide.