Weeds Are Increasingly Able to Withstand Glyphosate


The study, published in the scientific journal “PNAS Nexus,” suggests that glyphosate, considered a miracle cure for weed-free agriculture with higher yields, may be becoming less suitable in many regions of North America. The herbicidal effectiveness of glyphosate on test fields in those areas reportedly declined rapidly after a few years due to the development of resistance in unwanted plants within agriculture.

The authors, affiliated with the research service of the U.S. Department of Agriculture and the University of Illinois at Urbana-Champaign, analyzed data from multiple field experiments conducted over the past 25 years in the USA and Canada. During this period, Monsanto, now part of the German Bayer Group, established the glyphosate business under the brand name Roundup.

In North America, genetically modified seeds were introduced, designed by Monsanto to make crops resistant to glyphosate. Farmers in this region can apply the herbicide to fields with existing crops, allowing for intensive use. The widespread cultivation of corn and soybeans in the USA heavily depends on this herbicide today.

The European Union has not approved this application of green biotechnology. In the EU, glyphosate is used by farmers to clear fields of weeds before sowing crops. However, once crops like corn begin to grow, the herbicide is not applied, in contrast to many fields in North America, as it would lead to the death of the crops. It’s important to note that the results of the current study may not directly apply to the EU.

It Worked Perfectly at First

“The nature has done exactly what we were trying to avoid,” explained co-author Aaron Hager, a plant agriculture researcher from the University of Illinois, regarding the results. “It has adapted.”

The initial package solution for North America, consisting of new herbicides and resistant seeds, initially worked perfectly. However, over the years, an increasing number of weed species have mutated to the extent that they regrow on fields sprayed with glyphosate. Two of the examined species—velvet leaf and common lambsquarters—continue to be reliably controlled with glyphosate to this day. Nevertheless, given the observed changes, it is only a matter of time until resistance develops, even in these cases.

The effectiveness of the herbicide has decreased from 100 percent in many instances to 50, 30 percent, or even less, as noted by ecologist Marty Williams from the Ministry of Agriculture’s research service. Initial signs of adaptation typically manifest within two to three years after the initiation of glyphosate use.

31.6 Percent Loss of Control per Decade

The strategy of not relying solely on this one herbicide proved noticeably more successful in the long term. According to the lead author, Christopher Landau from the University of Illinois, glyphosate lost up to 31.6 percent of its weed control efficacy within a decade. When an older herbicide was additionally used, weed resistance increased by at most 4.4 percent.

The researchers affirm early warnings about dependence—warnings that were mostly ignored during the initial enthusiasm for glyphosate. Due to Monsanto’s commercial success, research and development of alternative methods were reduced, resulting in a current lack of viable alternatives. “Unfortunately, we were right,” commented Hager.

The research group’s recommendation to farmers is to employ diverse methods, apply agricultural chemicals alternately to the soil and leaves, cultivate different crops consecutively in a field, and use mechanical tools to remove weeds. Additionally, they advise farmers not to place unwavering belief in the promise of a miracle solution.