The objective of this work was to evaluate the sugarcane straw potential and the association between the straw and the commercial mix of the trifloxysulfuron sodium + ametryn to control itchgrass (Rottboellia exaltata L.). The experiment was developed in the Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF), Campos dos Goytacazes Rio de Janeiro State, Brazil, from September to November 2004. It was carried out in randomized blocks, with the treatments arranged in a factorial scheme: five layers of straw (0; 4; 8; 12 e 16 t ha-1) and five doses of trifloxysulfuron sodium + ametryn (0,0; 1,0; 1,5; 2,0 e 2,5 kg ha-1), with four replications. The herbicide was applied in post-emergence, when weeds (R. exaltata) height was between 5 and 10 cm. Number of weeds was evaluated at 15, 30, 45 and 60 days after herbicide application. The herbicide concentration that inhibits 50% of the weed emergency (I50) was determined. In the sixty day, the itchgrass plants were collected and dry biomass was determined. The interaction between straw quantity and doses of trifloxysulfuron sodium + ametryn was significant. Straw layer of 16 tha-1 without herbicide addition was efficient to control R. exaltata and the herbicide trifloxysulfuron sodium + ametryn at 2,5 kg ha-1 used alone was efficient to control this weed. Straw levels between 8 and 12 t ha-1 intercepted the herbicide and consequently, increased the I50 value. In other words, the concentration of the herbicide to inhibit 50% of the weeds growth was greater when there were 8 and 12 t ha-1 than when there was 4 t ha-1 of straw.
raw sugarcane; itchgrass; straw management; weed
