The very tool that simplified farming could be quietly undermining its future.
In fields across the world, a quiet revolution has transformed agriculture. Crops genetically engineered to survive powerful herbicides have allowed farmers to control weeds with unprecedented ease, contributing to billions of dollars in farm income 1 . Yet, behind this success story, weed scientists are observing troubling patterns that threaten to unravel these very gains. They're asking difficult questions about how long this technology can last and what happens when it fails.
The widespread adoption of herbicide-tolerant crops, particularly those resistant to glyphosate, has created a large-scale, unplanned experiment in evolutionary biology. When farmers use the same herbicide season after season, they apply intense selection pressure on weed populations 2 .
The result? Weed species that have evolved their own resistance, creating what are commonly called "superweeds."
"How long will current herbicides remain effective, especially in problematic weeds such as Russian thistle, Italian ryegrass and downy brome?" 3
Her concern is warranted. Before glyphosate-tolerant crops were introduced, only three weed species globally had developed resistance to glyphosate. Today, that number has jumped to at least 15 species, with nine confirmed in the U.S. alone 2 .
3 Resistant Species
Rigid ryegrass, goosegrass
9+ Resistant Species
Common waterhemp, horseweed, giant ragweed, Palmer amaranth
Weeds cause up to 31.5% reduction in global crop productivity
Annual economic losses of approximately $32 billion 4
Weed scientists recognize that resistance isn't their only concern. Herbicide-tolerant crops have created several additional challenges that extend far beyond the evolution of resistant weeds.
The controversy over dicamba, a herbicide used with genetically modified soybeans and cotton, illustrates another significant concern. Despite mitigation measures proposed by the EPA, dicamba has been notoriously prone to drifting and damaging neighboring crops that aren't genetically engineered to resist it 5 .
The 9th U.S. Circuit Court of Appeals noted "extensive evidence" that past damage from drifting dicamba was caused by "substantial non-compliance" with EPA's label restrictions, partly due to the "difficulty in complying with the complex and onerous label requirements" among farmers 5 . One court even noted that requirements for spraying only in low-wind conditions were compared to a "fairy tale" in blustery regions 5 .
Weed scientists also observe shifts in weed species—even without genetic resistance. Species that happen to be naturally more tolerant to certain herbicides increase in number when competing weeds are controlled 2 . This creates new management challenges as these naturally tolerant species fill the ecological niches left vacant by controlled weeds.
Another concern is "gene escape," where the herbicide-tolerance trait moves from crops to weedy relatives through cross-pollination. As one resource notes, "A crop such as Roundup Ready, Clearfield, or Liberty Link canola could pollinate nearby herbicide-susceptible canola, creating herbicide-resistant volunteers" that become weeds themselves in subsequent seasons 6 .
To understand how weed scientists are addressing these challenges, consider the work being done by the Pacific Northwest Herbicide Resistance Initiative. This collaborative project brings together researchers like Dr. Landau to identify and track herbicide-resistant weed populations 3 .
Collect samples from weed populations that survived herbicide applications
Grow suspect plants and apply precise herbicide treatments
Identify specific mutations responsible for resistance
Share confirmed resistant populations with farmers
| Weed Species | Herbicide Group Resisted |
|---|---|
| Kochia | Group 2, Group 9 (glyphosate) |
| Italian ryegrass | Group 1, Group 9 (glyphosate) |
| Downy brome | Group 1, Group 2 |
| Prickly lettuce | Group 2, Group 4 |
| Russian thistle | Group 2 |
The data collected from such initiatives is crucial. A new website launched in 2024 specifically tracks herbicide-resistant weeds in the Pacific Northwest, providing regularly updated information to help farmers make informed decisions 6 .
The results from this ongoing "experiment" are concerning. The Pacific Northwest now documents resistance in kochia, prickly lettuce, downy brome, Russian thistle, wild oat, Italian ryegrass, and others to multiple herbicide groups 6 . This research confirms that resistance is not isolated to a few species but is spreading across weed communities.
Weed scientists have developed multiple approaches to combat resistance, each playing a distinct role in integrated weed management.
Prevents repeated selection pressure from the same mode of action
Allows use of different herbicide options and tillage timings
Reduces the reservoir of resistant weed seeds in soil
Controls resistant weed escapes that survive herbicide applications
Identifies specific resistance mutations in weed populations
Destroys resistant seeds during harvest operations
Despite these challenges, weed scientists aren't suggesting we abandon herbicide-tolerant crops altogether. Instead, they advocate for a more nuanced approach called Integrated Weed Management (IWM) 2 .
"What kind of tools, ideas, rotations can we do to alleviate our reliance on these herbicides? However that goes, we need to be looking past herbicides."
The concerns weed scientists raise about herbicide-tolerant crops aren't meant to dismiss the technology's benefits but to ensure its sustainable use. As one extension publication aptly notes, "Herbicide-tolerant crops are a powerful tool in this toolbox," but they should not be the only tool 2 .
The solution lies in embracing diversity in weed control methods rather than seeking silver bullets. It requires looking beyond short-term convenience to long-term sustainability.
The greatest concern weed scientists may have is not about the technology itself, but about our willingness to adapt—to see weed management not as a simple chemical application but as a complex ecological dance that requires multiple steps and constant adjustment.