In their recent article, we feel that Wright et al. (1) [Dow AgroSciences researcher] misrepresented the potential for 2,4-dichlorophenoxyacetic acid (2,4-D)–resistant weeds in 2,4-D–resistant cropping systems and exaggerated the sustainability of their approach to addressing glyphosate-resistant weed problems in agriculture.
We were surprised that Wright et al. (1) stated that only "very few" 2,4-D–resistant weed species have evolved without quoting a specific number. We checked the database that they used to support this claim (2) and were alarmed to learn that, globally, 28 species across 16 plant families have already evolved resistance to the synthetic auxin herbicides, the mode of action to which 2,4-D belongs. Of these, 16 are known to be resistant to 2,4-D specifically (for comparison, 21 species are resistant to glyphosate globally). Furthermore, the claim that 2,4-D resistance is unlikely to evolve because of the complex and essential functions that auxin plays in plants is unsubstantiated.