Glyphosate and Saflufenacil: Elucidating Their Combined Action on the Control of Glyphosate-Resistant Conyza bonariensis

Synergic effects of glyphosate and saflufenacil have been reported to control Conyza spp. However, the mechanism of this synergic combination is unknown. The objectives of this study were to investigate the effects of the combination of glyphosate and saflufenacil on the control and resistance status of glyphosate-resistant (GR) C. bonariensis, as well as on oxidative stress and lipidic peroxidation. Glyphosate-resistant and glyphosate-sensitive (GS) biotypes were treated with different rates of saflufenacil, glyphosate, and glyphosate combined with saflufenacil. The combination of glyphosate (1480 g ae ha−1) and saflufenacil (≥15 g ha−1) presented the best control of GR plants compared with their individual effects. It also reduced the resistance factor from 19.6 to 4.6 (4.3-fold) and represents a good alternative for resistance management. The combination of glyphosate and saflufenacil resulted in higher oxidative stress and lipidic peroxidation compared with the effects of either herbicide alone. The oxidative stress and lipid peroxidation promoted by the combination of the herbicides occurred earlier after treatment and remained at higher levels over a longer period (12–192 h) compared with their individual results. The combined oxidative stress and lipid peroxidation at high levels over a long time is likely to be one reason that the combination of glyphosate and saflufenacil effectively controls GR C. bonariensis.