Resistance of Amaranthus hybridus to glyphosate: detection, mechanisms involved and alternatives for integrated management

Background:  Glyphosate-resistant Amaranthus hybridus biotypes have been observed in Rio Grande do Sul (RS) crops. Their impact on soybean yield is high due to rapid growth and competitiveness. Investigating the resistance mechanism guides management strategies.

Objective:  To confirm the evolution of glyphosate-resistant A. hybridus biotypes in southern RS, identifying the resistance mechanism and proposing alternative management strategies.

Methods:  Dose-response curve studies, investigation of EPSPS gene mutation, and analysis of integrated management practices were conducted to characterize glyphosate resistance in A. hybridus biotypes.

Results:  Three Amaranthus hybridus biotypes from Aceguá, Bagé, and Rosário do Sul (RS) exhibit triple mutations in the EPSPS gene, providing glyphosate resistance. Resistance levels are high (>10). Alternative mechanisms of action to glyphosate such as glufosinate-ammonium or 2,4-D choline salt (Enlist technology) in post-emergence and sulfentrazone + diuron (pre-emergence) control resistant plants without compromising soybean yield.

Conclusions:  Confirming Amaranthus hybridus resistance to glyphosate requires alternative control measures. Combining alternative mechanisms of action, such as those available in new technologies, is important and should be the main action in a control program. Important aspects of integrated management should be prioritized combined with herbicide use.

Keywords:
Soybean; Pre-Emergent; Integrated Weed Management; Glyphosate