This work evaluatedthe herbicides selectivity acetolactate synthase inhibitors and photosyntheticII applied in post- emergency in palisadegrass (Brachiaria brizanthacv. Marandu) and signalgrass (Brachiaria decumbens cv. Basilisk) plantsin field conditions and their effect in seed quality. Treatments tested in gha-1 were: imazethapyr at 100, chlorimuronethyl at 15, nicosulfuronat 50, bentazon at 720, atrazine at 3.000, and control plot. Two field trialswere set up on complete randomized block design with four replicates; laboratorystudies were carried out in a complete randomized design, with 16 repetitions.All the herbicides showed some visual effect of phytotoxicity in both evaluatedcultivars. Nicosulfuron showed the highest visual damages in the cultivars.Dry mass production in the initial growth stage of B. brizantha decreasedwith application of nicosulfuron and atrazine; dry mass production of B.decumbens was reduced just by the nicosulfuron herbicide. Seed quality ofboth cultivars was affect by nicosulfuron herbicide only, which induced theseed dormancy of B. decumbens and decreased the normal seed percentageand, like the atrazine, increased the dead seeds.
