The weed dayflower, Commelina spp., can survive in a great diversity of environments, what makes its control difficult. In coffee plantations of the Zona da Mata, Minas Gerais - Brazil, glyphosate is repeatedly applied to control weeds, but Commelina benghalensis and C. diffusa have not been successfully controlled. To confirm such fact and to verify the effect of increasing doses of glyphosate (720, 1,400, 2,160, 2,880 and 3,600 g a.i. ha-1) on these weed species, an experiment was installed in a randomized block design with six replications. The rates of herbicide were applied in the flowering period of plants grown in polyethylene boxes 10 cm high, 27.5 cm wide and 39.5 cm long, in unprotected environment. The effectiveness of the treatments was evaluated through the percentage of weed control related to the check treatment (no herbicide), and by the shoot dry biomass that survived the treatments. C. benghalensis was efficiently controlled by glyphosate, but C. diffusa presented herbicide tolerance. The control of C. benghalensis was above 94%, starting from the smallest rate, 25 days after treatments (DAT), and it was 100% in all the doses at 63 DAT. For C. diffusa, in general, as the doses of glyphosate increased, the shoot dry biomass became smaller. However, even with the three higher doses, when up to 98.3% of control at 46 DAT was observed, plant recovery occurred at 88 DAT. Under the conditions of this experiment, glyphosate provided an excellent control of C. benghalensis starting from 720 g a.i. ha-1, 25 DAT. However, excellent control of C. diffusa for over 60 DAT was only achieved with glyphosate rate starting from 2.880 g a.i. ha-1.
dayflower; chemical control; tolerance
