Research Protocol for Approval of Drift-Reducing Adjuvants for Dicamba in Brazil

The increased use of soybean cultivars genetically modified to be tolerant to dicamba is encouraging the development of new adjuvants for drift reduction. In this context, the objective of this work was to develop a test protocol for the approval of tank-mix drift-reduction adjuvants for dicamba in Brazil. A candidate adjuvant undergoes a set of droplet-spectrum tests in a paired manner with a standard adjuvant (Xtend Protect at 1.0% v/v). The protocol is based on comparing the new adjuvant with the standard, spraying them in a tank mixture with dicamba and glyphosate using a Teejet TTI 11003 spray nozzle at 5 bar. This solution contains XtendCam (480 g/L dicamba diglycolamine salt at 1.0 L/ha mixed with Roundup Transorb R [588 g/L glyphosate potassium salt at 2.0 L/ha]) at 100 L/ha. Because some of these adjuvants contain components sensitive to the pumping process, reducing its effectiveness, a sprayer equipped with a piston pump was used to simulate the pumping recirculation process, providing 5 bar to a nozzle inside a spray chamber, in which the droplet spectra generated over time was evaluated by a Sympatec Helos laser-diffraction particle analyzer. Four recirculation levels were considered: not pumped and 4, 10, and 16 cycles (one cycle means that the solution passed through the pump once). The volume median diameter (VMD) and the percentage by volume composed of droplets smaller than 150 μm (V150) data were used as parameters to compare the adjuvants through a statistical analysis. To be approved, an adjuvant must offer an VMD equal to or greater and V150 equal to or less than that generated by the standard adjuvant. Ten candidate adjuvants were evaluated, and only one was approved. The most frequent reason for failure was the generation of V150 higher than that generated by the Bayer adjuvant (Xtend Protect).