Mixtures of herbicides for the control of multiple resistant Conyza sumatrensis in soybean pre-sowing burndown

The objective of this study was to evaluate the effectiveness of synthetic auxins in the control of Conyza sumatrensis in mixtures for use in the first application, and the effectiveness of burndown herbicides alone or in mixtures for use in the second application, in soybean pre-sowing. Experiment 1 consisted of auxin herbicides (fluroxypyr or dicamba) in mixtures with herbicides (glyphosate, glufosinate, saflufenacil, carfentrazone, and chlorimuron) used for the first application in pre-sowing. Experiment 2 consisted of burndown herbicides (diquat, glufosinate, glyphosate, chlorimuron, saflufenacil, and carfentrazone), alone or at mixtures, used for sequential application in pre-sowing. For the first application, the effectiveness of glyphosate + dicamba or fluroxypyr was low and must be complemented by the addition of a PPO-inhibiting herbicide, mainly saflufenacil. The mixture of glufosinate, instead of glyphosate, with synthetic auxin was more effective, even increasing with the addition of saflufenacil. For the second application, with burndown herbicides, glufosinate was superior and effective when mixed with saflufenacil. For the first application in soybean pre-sowing, glyphosate or glufosinate + synthetic auxin + saflufenacil are effective for the control of C. sumatrensis. For the second application, glufosinate at mixtures is effective in controlling C. sumatrensis.