A few days after the application of the 2,4-D herbicide, either during V4 or V6, visual symptoms of toxicity were observed in the shoot of the soybean plants in treatments with doses equal to or greater than 20 g ha-1 (Figure 2). At this dose, the symptoms were mild and were characterized by a discrete bending of the main stem relative to its vertical axis. However, strong toxicity symptoms were observed at doses equal to or greater than 30 g ha-1, which were characterized by acute stem bending, leaf hyponasty, and reduced growth, as described in detail by Robinson et al. (2013) for the soybean crop. These toxicity symptoms are typical of sensitive dicotyledonous plants treated with auxin herbicides, since they cause a hormonal imbalance affecting protein synthesis, osmotic regulation, and cell wall plasticity when they bind to proteins in the cell membranes (Cobb and Reade, 2010). It is worth emphasizing that Robinson et al. (2013) showed that soybean yield was only affected when the toxicity reached a minimum of 20%, which coincided with the application of doses equal to or greater than 29 g ha-1 during V5.