Eficácia e seletividade do iodossulfurão-metilo-sódio +mesossulfurão-metilo na cevada dística (Hordeum distichum L.)

Abstract

During the vegetation periods 2012/13 and 2013/14 four field trials were carried out (two per year) on the Experimental Farm of Almocreva (Beja), with the objective to study the efficacy and selectivity of the herbicide iodosulfuron-methyl-sodium (50 g L-1) + mesosulfuron-methyl (7.5 g L-1) in malt barley. In both trials three application rates were applied (5.0 + 0.75, 7.5 + 1.125 e 10.0 + 1.5 g a.i ha-1) at two different development stages of both weeds and the barley crop. In the year 2012/2013, the herbicide was applied when the weeds were in the development stage of three to four pairs of leaves, and the crop, at the beginning of tillering that corresponded the stage 20 of Zadoks scale (first application timing). The second application timing was when the weeds were at the development stage of six to seven pairs of leaves, and the crop at the complete tillering (29 Zadoks` stage). In the year 2013/2014, the first application timing was when the weeds were in the development stage of five to six pairs of leaves, and the crop at the main culm (24 Zadoks` stage). The second application timing was when the weeds were at the development stage of seven to eight pairs of leaves, and the crop at the third visible node (33 Zadoks` stage). The results show that the first application date at earlier weed and crop development stages did not lead to an increase in efficacy when compared to the later application timing, and for application rates. Using the recommended application rates (7.5 + 1.125 e 10.0 + 1.5 g a.i ha-1) an increase in efficacy could be observed in both years and application dates when compared to the lowest application rate (5.0 + 0.75 g a.i ha-1), but no significant interaction between application rates and dates was obtained. In contrast to 2013/14, a significant reduction in crop yield was observed in 2012/13 when anticipating the application date. This effect is attributed to phytotoxicity caused by the herbicide when applied at an early tillering stage.