The continuous use of herbicides from the chemical groups triazines and substituted ureas has imposed a selection pression upon tolerant species of crabgrass (Digitaria spp), in sugarcane plantations, causing the phenomenon of weed species shift, by reducing the populations of susceptible crabgrass species and increasing the proportion of tolerant species of this weed genus. In order to scientifically elucidate this phenomenon, this research was developed, under field conditions, with the following objectives: a) to evaluate the agronomic efficacy of herbicides used in sugarcane crops to control D. nuda and b) taxonomic identification of Digitaria species selected by herbicides in areas that received repetitive applications. Eight herbicide treatments (ametryne, diuron, tebuthiuron, diuron + hexazinone, imazapyr, isoxaflutole, metribuzin e imazapic), applied during pre-emergence were used, and control percentage was evaluated at 15, 30 and 60 days after herbicide application (DAA). The identification of species of Digitaria population was carried out following analytical identification key, through the observation of plant morphologic characteristics. The specie D. nuda was selected by herbicide repetitive applications. The specie D. nuda was controlled in a lower level by the herbicides diuron, tebuthiuron, diuron + hexazinone, imazapyr and imazapic. However, the herbicides ametryne, isoxaflutole and metribuzin showed good efficacy to control until 60 DAA.
herbicide tolerance; susceptible specie; Digitaria spp
