The silver bullet that wasn’t: Glyphosate’s declining weed control over 25 years

By Lauren Quinn
Published December 5, 2023 on University of Illinois Urbana-Champaign

It has been a quarter century since corn and soybeans were engineered to withstand the withering mists of the herbicide glyphosate.

Initially heralded as a “silver bullet” for weed control, the modified crops and their herbicide companion were quickly and widely adopted across corn and soybean-growing regions of North America.

In the years that followed, though, weeds targeted for eradication quietly fomented a rebellion.

A study led by scientists from the U.S. Department of Agriculture’s Agricultural Research Service and the University of Illinois Urbana-Champaign (U of I) takes a retrospective look at glyphosate efficacy after the engineered crops were commercialized.

Amassing data from annual herbicide evaluation trials at land-grant universities across the United States and Canada, the researchers show a significant and rapid decline in glyphosate control for all seven major weed species they examined.

“Our analysis represents one of the largest cumulative measures of how weed communities have adapted to the simplified weed management tactics adopted at an unprecedented scale throughout North America,” said Chris Landau, postdoctoral researcher for the ARS.

Less Responsive

Although glyphosate provided superior weed control in the early years, most of the weeds in the dataset showed signs of adaptation to the chemical in just two to three years.

Within a decade, weeds were up to 31.6% less responsive to glyphosate, with further linear declines as time went on.

“Nature did exactly what we were trying to help people avoid — it adapted,” said co-author Aaron Hager, professor and faculty Extension specialist in the Department of Crop Sciences at the U of I.

In addition to loss of control, glyphosate efficacy became more variable over time.

“When glyphosate-tolerant crops were first adopted, weed control was high in every environment; however, year after year glyphosate performance became less consistent,” said co-author Marty Williams, ARS ecologist and affiliate professor of crop sciences.

“For example, glyphosate provided nearly 100% control of a given species in most plots in the mid-1990s. But over time, acceptable weed control became rarer, often deteriorating below 50%, 30% and worse.”

These patterns were derived from annual herbicide evaluation trials conducted at land-grant universities, usually in conjunction with their respective Extension services.

These carefully managed trials test new and existing herbicides against numerous common and troublesome weed species.

Mining Data

A couple years ago, Landau, Hager and Williams mined historical data from U of I herbicide evaluation trials to look at the effect of climate change on weed control in Illinois corn and soybean fields.

When they decided to look at the history of the country’s most widely used herbicide, the team knew it would be more powerful to access data beyond Illinois.

In cooperation with 24 institutions throughout North America, Landau compiled a massive database representing nearly 8 million observations from 1996 to 2021.

For the current study, he winnowed the data down to fields that tested glyphosate annually, alone or in combination with a preemergence herbicide.

Landau also narrowed the target weeds to seven major players: annual and giant ragweed, horseweed, lambsquarter, Palmer amaranth, velvetleaf and waterhemp. In the end, the dataset represented trial data from 11 institutions.

Pre-Emerge Trials

After documenting patterns of glyphosate control and variability over time, Landau reran the analysis for plots in which a preemergence herbicide had been applied before glyphosate. The results were strikingly different.

“Adding a preemergence herbicide effective against the target weed species significantly improved control and reduced variability of glyphosate over time,” Landau said. “The most we saw for any weed species was a 4.4% loss of control per decade, compared to 31.6% loss for glyphosate alone.”

“Having already seen loss of control with ALS- and PPO-inhibitors, we eventually reached the point where we felt it necessary to come out with some very specific recommendations for glyphosate,” Hager said.

“Because if we didn’t, we had a pretty good idea of where this was going to end up. And, unfortunately, we were right.”

Patterns Only

The dataset for glyphosate can only show patterns, not explanations. While herbicide resistance might be to blame — the issue has become a major problem in agricultural weeds in recent decades — it’s not the only reason glyphosate may have loosened its grip.

Landau noted that two species he tracked in the analysis — velvetleaf and lambsquarter — have not yet had a confirmed case of glyphosate resistance anywhere in the world. Yet both followed the same trends as glyphosate-resistant species in the dataset.

Landau said herbicide pressure, or concurrent climate changes, over the past 25 years may have selected for larger leaf area or earlier emergence, both of which could help weeds survive glyphosate.

Regardless of the mechanism, the pattern is clear: silver bullets for weed control don’t exist. The researchers urge diversification in chemistries, including soil- and foliar-applied products; crop rotation patterns and mechanical controls.

And if another silver bullet is marketed in the future? Hager said the glyphosate story should serve as a cautionary tale.

“Let’s imagine a company says they have the next silver bullet. It’s going to enjoy a huge market share almost instantaneously,” he said.

“But it needs to come with a stewardship plan to better preserve that chemistry over time. Why would we think nature would behave any differently? It won’t.”

Read the original article on University of Illinois Urbana-Champaign College of Agricultural, Consumer & Environmental Sciences »

How Safe Is Glyphosate Chemical Backed by Trump? What the Science Says

By Jasmine Laws
Published February 20, 2026 on Newsweek

U.S. President Donald Trump recently signed an executive order that would push for a greater supply of glyphosate-based herbicides, leaving scientists and environmentalists deeply concerned.

The president said in the order, titled “Promoting the National Defense by Ensuring an Adequate Supply of Elemental Phosphorus and Glyphosate-Based Herbicides,” that the chemicals play “a critical role” in American farming and a lack of access to them would “critically jeopardize agricultural productivity” and the country’s food systems.

However, the International Agency for Research on Cancer (IARC) labeled glyphosate as “probably carcinogenic to humans” in 2015, and other studies have indicated its harm to human health.

“This is not a chemical with zero risk,” Melissa Perry, a professor of public health at George Mason University, told Newsweek. “The weight of independent scientific evidence supports caution, not complacency.”

Despite its studied health impacts, glyphosate remains popular because it is “broad-spectrum, effective, and supports large-scale agriculture,” Perry said. “Its effectiveness and relatively low acute toxicity compared to some older herbicides have contributed to the perception that it’s benign.”

When approached for comment, the Department of Health and Human Services pointed Newsweek to a statement from Health Secretary Robert F. Kennedy Jr.: “Donald Trump’s Executive Order puts America first where it matters most—our defense readiness and our food supply. We must safeguard America’s national security first, because all of our priorities depend on it. When hostile actors control critical inputs, they weaken our security. By expanding domestic production, we close that gap and protect American families.”

Why It Matters

Scientists have expressed concerns that increased use of glyphosate-based herbicides could increase health risks, including cancer, among humans and other species and damage biodiversity.

Trump’s move also contradicts the fundamental policies of Kennedy’s Make America Healthy Again campaign, as tackling pesticide and herbicide usage that harmed public health was one of his main objectives. The health secretary’s apparent support for the order has sparked a backlash among MAHA proponents, who have expressed feeling betrayed.

What To Know

Glyphosate, the chemical in Bayer-Monsanto’s Roundup, is the most commonly used herbicide in the U.S. The chemical’s use has also increased almost 15-fold globally, according to studies, since the introduction of the company’s Roundup Ready crops—genetically engineered glyphosate-tolerant crops that were first used in 1996.

Since the introduction of the glyphosate-based herbicide, Bayer—which acquired Monsanto in 2018—has been hit with thousands of lawsuits alleging the company failed to warn people that its popular weedkiller could cause cancer. The agrochemical maker proposed a $7.25 billion settlement on Tuesday to settle the lawsuits.

About 200,000 Roundup-related claims have been made against Bayer, which includes more than 125,000 plaintiffs who have sued since 2015, according to the settlement documents.

The IARC concluded that glyphosate was “probably carcinogenic to humans,” that there was also “‘strong’ evidence for genotoxicity, both for ‘pure’ glyphosate and for glyphosate formulations.” Genotoxicity is a property in certain substances that can damage the genetic material in a cell, which can lead to cell mutations and diseases such as cancer.

To make its evaluation, the IARC reviewed about 1,000 studies “by independent experts, free from vested interests.”

Other studies and reviews have concluded that glyphosate exposure is associated with a higher risk of non-Hodgkin lymphoma, a cancer of the lymph system. Those exposed to glyphosate-based herbicide saw their risk of the cancer increase by 41 percent, a 2020 study found.

Based on the research, Perry said, “it is inaccurate to describe glyphosate as unequivocally safe.” She added that it was “concerning” that glyphosate use had expanded dramatically in the country, “even as evidence of potential health risks has grown.”

She said the population’s increased exposure to the chemical “deserves careful scrutiny.” Beyond cancer concerns, the harmful chemical is now “ubiquitous in soil, water, and food systems,” she added.

“That level of environmental persistence raises legitimate ecological and long-term human health questions,” Perry continued.

The environment can also suffer from the chemical, experts have warned. Glyphosate can “harm biodiversity” by “killing plants that are not weeds (non-target plants), and it’s harmful to fish and other endangered species,” Stephanie Eick, a professor of environmental health at Emory University, told Newsweek.

It also has “a long half-life in soil, meaning that it does not easily break down and can remain in the soil for up to several months and potentially harm soil,” she added.  

What People Are Saying

Stephanie Eick, a professor of environmental health at Emory University, told Newsweek: ”From my perspective, I think that glyphosate is harmful to human health. There are also studies in animals that show that glyphosate can lead to kidney and liver damage, even at relatively low doses. I think this update is concerning because glyphosate is already very widely used in agricultural settings, which ultimately is a major way for which humans are exposed (for example by eating foods that contain glyphosate). Ultimately, it’s possible that this ban will lead to an increase in the amount of glyphosate that’s used, which in turn could lead to higher levels of glyphosate exposure for humans, leading to increased health risks.”

She added: “While I am very concerned about this executive order, there are actions that we can take on an individual basis to limit our intake of glyphosate. Examples of this include choosing organic products when possible (organic products are free of synthetic chemicals, including glyphosate). If that’s not possible, also remember to wash fruits and vegetables thoroughly before eating them, this will help to remove potential pesticide residue.”

George Kimbrell, the legal director at the Center for Food Safety, said in a statement: ”This Trump Executive Order follows a long pattern from the administration: sound and fury, ultimately signifying nothing. Executive orders do not have the force and effect of law without new authority from Congress and here cannot magically give Monsanto immunity for the harms of its toxic glyphosate products. 

“In addition to being legally meritless, the EO is factually unmoored from reality. The Trump Administration has demonstrated no threat to the continued availability of glyphosate, and in any case there are literally hundreds of other herbicides available to farmers and others. This EO is a transparent attempt to influence the Supreme Court to grant glyphosate-maker Monsanto/Bayer and other pesticide behemoths immunity from liability for the harms caused by their products. It also represents the Trump administration betraying MAHA yet again and a feeble attempt to divert attention from the disastrous effects of Trump tariffs on the farming community.”

What Happens Next

Despite the chemical’s history of litigation and harm, Trump said in the executive order, “United States-based production of glyphosate-based herbicides is central to American economic and national security.” He has instructed the secretary of agriculture to ensure a “continued and adequate supply of elemental phosphorus and glyphosate-based herbicides.”

In a polarized era, the center is dismissed as bland. At Newsweek, ours is different: The Courageous Center—it’s not “both sides,” it’s sharp, challenging and alive with ideas. We follow facts, not factions. If that sounds like the kind of journalism you want to see thrive, we need you.

Read the original article on Newsweek »

Glyphosate resistance is not inevitable: changes you can make

By Siobhan Walsh
Published February 20, 2026 on Irish Farm Journal

Glyphosate resistance in Italian ryegrass is dotted around England. Currently, about five cases have been confirmed with more being examined and expected to be confirmed. The cases are independent. They’re not linked and they come about due to a number of different factors, from application timing and quality to a reliance on glyphosate and a lack of variation in control.

One thing that John Cussans, weed science principal agronomist at ADAS, made clear at his talk at Crop Tec show in Birmingham last week is that for every case there is a farmer behind it who is dealing with a weed issue, increased costs and curtailed operations on their farm.

John explained some of these factors: “Where there is too much reliance on glyphosate across the whole rotation for all your weed control. You’re reducing the amount of mechanical weeding. 

“You’re reducing the amount of cultivation – the number of cultivation timings and how intense that cultivation is. You’re moving towards a low disturbance drill system that’s taking away another mechanical weeding event you used to get with a drill. He said older establishment systems gave nearly 100% control of weeds before sowing.

“Combine this with lots of stubbles where there is no weed control on the stubble, trying to establish a spring crop where you’ve got large, well-established ryegrass plants and you’re trying to use high doses of glyphosate and then you don’t have any more mechanical weeding before you go into the crop. 

“If you think about it, so much of your weed control across the whole rotation is coming from glyphosate and it’s that over-reliance on glyphosate that’s driving the resistance.

“We’re not saying it’s the use of glyphosate over time or how much is being used. It’s that reliance. That means we’re seeing cases popping up right across the country [UK]. It’s because it’s not spreading, it’s being selected for in that way.”

John thinks farmers have become complacent with glyphosate and how it is applied. The timing of application, the weather at application and the quality of the water being used to spray the product all impact efficacy.

The weeds researcher said he is not telling people not to use low-disturbance establishment systems or not to leave over-winter stubbles for birds. 

These are all important, but he said farmers need to monitor weeds and for example if they see weeds emerging on winter stubbles, use some mechanical weeding to take out that patch.

Not inevitable

Where caution is taken and given that information John wanted to be clear that glyphosate resistance is not inevitable and that is clear from the fact that there is no cluster of resistance cases. 

The first case of glyphosate resistance in the UK was in Kent, where there was a lot of ryegrass in the crops and the weed abundance took hold. 

The farmer continues to grow arable crops and is managing the issue, but needs a lot of mechanical weeding and early intervention to keep weeds under control, adding work and cost to his system.

What causes resistance?

When looking at the resistance cases it is clear that all the locations where it occurs have a number of factors in common. 

There is no one individual thing that stands out as causing the resistance.

Factors that can contribute to glyphosate resistance:

·  A heavy reliance on glyphosate.

·  Low disturbance establishment systems.

·  Long durations of stubble post-harvest where there is no effective weed control. Weeds get too big to control.

·  Big weeds resulting in well-rooted and tillered ryegrass plants being sprayed with high doses of glyphosate before sowing.

·  Incorrect glyphosate application.

John made the point that traditional establishment systems have a mechanical weeder in some form. A power harrow for example will destruct weeds in its path, but minimum-tillage drills do not have this.

He also noted that operator decisions drive results. Applying at the wrong time or under-dosing can result in poor control.

Spraying at the wrong boom height will leave strips of weeds uncontrolled.

In the UK, there are stewardship guidelines to prevent glyphosate resistance build up and to ensure it is being used in the correct manner beside water for example.

The guidelines aim to:

·  Minimise weed survivors.

·  Maximise efficacy.

·  Use alternative herbicides where possible.

·  Monitor success.

·  A wider adoption of alternatives to glyphosate – in-crop herbicides, mechanical control.

·  Every single field and farm must monitor the success of a glyphosate application.

·  Implement free-resistance testing.

Spray water

The type of water that you spray with also needs to be examined when spraying glyphosate. 

Hard water can negatively impact the herbicide’s efficacy as it can result in poorer uptake through the leaf.

This is not true of all plant protection products, but does particularly impact glyphosate and some other herbicides.

Hard water should be treated with a conditioner. Growers can get a hard water metre or send water off to the lab for testing. 

Rain water is ideal for spraying glyphosate as it is not hard. If you can you should prioritise collected rain water for glyphosate spraying or dilute hard water with rain water.

If water is hard and needs a condition then this conditioner should be added to the water before you add in the glyphosate. You should pre-mix the conditioner with the water and then add in the glyphosate.

John also added that farmers should not be cutting glyphosate rates, particularly if using a generic product.

Comment

Glyphosate is an important product for weed control across tillage farms and livestock farms. Many reduced tillage farms will tell you it is a herbicide that is essential in their tool box. 

Those farmers in low-disturbance tillage systems need to be vigilant and perhaps be prepared to cultivate at times when they don’t want to in order to keep the herbicide working. 

All farmers need to pay attention to the success of the herbicide and all farmers will probably admit that they could apply it at better times or choose products more carefully for poorer weather. 

From what John says, little changes can go a long way when combined together to protect the herbicide. So, apply at the right time, the right rate, with the right water.

Read the original article on Siobhan Walsh »

Scientists Say This Potential Carcinogen May Be Lurking in Your Garden

By Korin Miller
Published February 20, 2026 on AOL.com

Glyphosate is an ingredient found in several herbicide products, including those from a major brand that has been in the news for settling a lawsuit around glyphosate’s potential link to cancer. Recent research links glyphosate to Hodgkin’s lymphoma and raises questions about the ingredient’s carcinogenic properties, however, more research is still needed.

Meet the experts

Kelly Johnson-Arbor, M.D., a toxicologist at MedStar Health; Jamie Alan, Ph.D., an associate professor of pharmacology and toxicology at Michigan State University.

Here, experts dig into the science and what they want you to know to protect your health.

What is glyphosate?

Glyphosate is an herbicide that’s widespread in the environment. “It was initially registered as an herbicide in the United States in 1974 and has been used as a primary ingredient in various formulations of weed killer,” explains Kelly Johnson-Arbor, M.D., a toxicologist at MedStar Health.

An estimated 81% of the population has had a recent exposure to glyphosate, according to the Centers for Disease Control and Prevention (CDC). People are typically exposed to the weedkiller through food, skin contact, and from breathing in particles in the air, per the CDC. The biggest food sources of glyphosate include fruits, vegetables, and cereals.

The Environmental Protection Agency (EPA) has set tolerance levels for glyphosate on crops, and it varies by type. The tolerance levels range from 0.1 to 400 parts per million, depending on the food.

What does the science say?

There is some data to support the link between glyphosate and cancer, but more research is needed.

A 2025 study published in the journal BMC Environmental Health exposed rats to drinking water contaminated with glyphosate alone and two commercial glyphosate-based formulas (one being Roundup) daily for two years. The doses were 0.5, 5, and 50 mg/kg of body weight, which are levels currently considered safe by regulatory agencies. Rats in all three exposure groups developed more benign and cancerous tumors in multiple areas of the body.

The researchers found that the exposed rats were more likely to develop early-onset cancer and die young from rare cancers, including leukemia, liver, ovary, and nervous system tumors. Half of the deaths from leukemia happened when the rats were less than a year old, which correlates to 35 to 40 years old in humans.

An older scientific analysis also found that exposure to glyphosate increased the risk of developing certain cancers by more than 40%.

As of now, the World Health Organization’s International Agency for Research on Cancer (IARC) lists glyphosate as “probably carcinogenic to humans.” However, the EPA says that “there are no risks of concern to human health when glyphosate is used in accordance with its current label,” noting that the agency doesn’t agree with the IARC’s conclusion.

For what it’s worth, some research has also noted that glyphosate may cross the blood-brain barrier, raising concerns that it could interfere with brain and nerve health, too.

What do experts say? 

It’s important to stress that the link between glyphosate and cancer in humans is still being explored. While animal studies have suggested it, the link is less certain in humans.

“It’s likely a multi-factorial process,” says Jamie Alan, Ph.D., an associate professor of pharmacology and toxicology at Michigan State University. “There is evidence that glyphosate damages DNA, causes inflammation, and causes oxidative stress, all of which may contribute to cancer formation.”

But there’s still a lot we don’t know. “At this time, the connection between glyphosate exposure and adverse health effects in humans is not fully understood,” Dr. Johnson-Arbor says.

How to protect yourself

In a perfect world, you’d avoid using pesticides and simply pull weeds by hand, Alan says.

If you still want to use pesticides around your home, Alan recommends wearing a mask and gloves and washing your hands after use. “Importantly, after you apply it, wait for it to dry,” she says. “It will be taken up into the plant after a short time, but while the plants are wet, it [may] transfer to you.”

The advice also applies to people spraying large fields, but those who are exposed to higher levels and who have more frequent exposure should consider additional protective equipment and possibly a respirator, Alan says.

It’s easy to brush off these concerns if you don’t garden or use weed killer, but it’s important to stress that glyphosate is widespread in the environment and has been detected in produce and grains.

If it’s within your budget, Alan recommends doing your best to choose organic when you buy thin-skinned produce like berries and leafy greens, along with grains. “For bananas and fruits and veggies with thick skin, it likely would not make a difference,” she says. While these organic products may still contain trace amounts of glyphosate, research suggests that it’s at far lower levels than conventional goods.

Dr. Johnson-Arbor points out that your body is equipped to deal with exposure to pesticides and will often eliminate them from your body when going to the bathroom. But it’s unclear how much repeat exposure or exposure at high levels may impact your body—and your health—in the future.

Again, these findings are preliminary and more research is needed. Before you panic, remember that the EPA also says the risks are low when used in accordance with the current label.

Read the original article on AOL.com »

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