Herbicide rates are established to be applied under a range of environment and crop management conditions. Sometimes, herbicide rates can be reduced and, yet, suppress weed interference in a crop. The aim of this study was to test rate reduction for the herbicide acifluorfen + bentazon to control beggarticks (Bidens spp.) and arrowleaf sida (Sida rhombifolia), at different weed development stages relative to soybean emergence time. A field experiment was carried out in Passo Fundo, RS, with treatments consisting of five application times and four Doble rates (1,25; 1,5; 1,75 e 2,0 L ha-1), plus two checks, (without weed control and with weeds removed by hand, at the same times of herbicideapplication. Considering all the situations tested, the level of arrowleaf sida control varied from 80 to 99%, whereas that of beggarticks varied from 78 to 99%. For the whole cycle evaluation of the target species, the best control was found to be application in the four-leaf plants. Increasing acifluorfen + bentazona rate in the1.25 to 2.0 L ha-1 range results in a positive linear soybean yield return.. The most biologically efficient rate was the 2.0 L ha-1 labeled rate. The rates close to 75% of the labeled rate provided thebest economic return.
Bidens pilosa; Bidens sulbalternans; Sida rhombifolia; herbicides; spraying time; yield loss
