INTERFERENCE OF SOURGRASS PHENOLOGICAL STAGE ON THE EFFECTIVENESS OF GLYPHOSATE HERBICIDE

Abstract

Efficient weed chemical control with post-emergence herbicides depends upon the phenological stage of the target plants in the moment of application. In this sense, plants’ phenological stage is an important variable to be considered in the production environment, once it interferes on product’s efficacy and demands reallocation of the recommended rates. Thus, this work was developed with the objective of evaluating glyphosate-susceptibility of sourgrass influenced by the phenological stage at the moment of application. Two similar experiments were carried out, in which treatments were organized according to a 8x5 factorial scheme, where eight were the rates of glyphosate herbicide (0, 45, 90, 180, 360, 720, 1440, 2880 g ha-1) and five were the phenological stages of sourgrass. Compared to the dry mass variable, it was observed that the variable percent control promoted better estimative of sourgrass susceptibility to glyphosate considering different phenological stages; for that variable, calculating DL80 reached excellent estimative of species herbicide susceptibility, providing the equation y = 26.276x – 112.42, i.e., increasing glyphosate rate by 150 g ha-1 was necessary to reach DL80 for each 10 units of plants’ development in BBCH scale.