Chemical control of multiple herbicide-resistant Amaranthus: A review

: Plants of the genus Amaranthus are important agricultural weeds that compromise food production worldwide. Several biological characteristics make these plants thrive in the environment and cause significant yield losses in many crops. Among the seven most important Amaranthus species in the Americas, four have populations with resistance to more than one mode of action ( A. hybridus , A. palmeri , A. retroflexus , and A. viridis ). While multiple herbicide-resistance in Amaranthus species is widespread, chemical control remains as one of the most important tools against those weeds. In this review, we compiled data from multiple sources on the efficacy of different herbicides across the most common modes of action that are used in Amaranthus management. Both PRE and POST herbicides are discussed, as well as the key factors to be considered when using each one of them. Residual PRE herbicides bring several advantages when managing Amaranthus species. These herbicides can avoid weed interference in the initial stages of crop development and provide a more favorable situation for weed control in POST. In addition, including PRE herbicides allows for the addition of alternative modes of action that are not available as POST treatments. Most POST herbicides have limitations regarding weed size and herbicide resistance status. Applying POST herbicides at the early growth stage of weeds is crucial to obtain efficacy. Finally, weed management sustainability depends on herbicides. Therefore, herbicide use should be combined with other weed control methods to avoid herbicide resistance evolution.