Weeds Are Now Developing Resistance to Herbicides They’ve Never Been Exposed To

October 13, 2021 | Pesticide use in conventional chemical-intensive farming is so pervasive that weeds are developing resistance to herbicides they have never encountered before. According to research published in Plant and Cell Physiology and New Phytologist, the notoriously difficult-to-control weed waterhemp (Amaranthus tuberculatus) is outpacing commercial crops in its ability to detoxify after herbicide exposure. “This is probably the first known example where waterhemp has evolved a detox mechanism that a crop doesn’t have. It’s using a completely different mechanism, adding to the complexity of controlling this weed,” says Dean Riechers, PhD, study coauthor and professor at University of Illinois. Analyses conducted by the University of Illinois scientists determined that waterhemp developed a process completely novel and separate from how corn detoxifies the compounds. While it is usually the cytochromes P450 enzymes that break down hazardous molecules, waterhemp uses different enzymes called glutathione S-transferases (GSTs). It is increasingly clear that herbicide use is the prevailing driver of the ever-evolving adaptability of waterhemp plants. [Strom, Seth et al. Metabolic Pathways for S-Metolachlor Detoxification Differ Between Tolerant Corn and Multiple-Resistant Waterhemp. Plant and Cell Physiology and New Phytologist. 62(11):1770–1785, 2021.]