Replacing glyphosate in the garden won’t be easy

The city of Davis, California, started phasing out the use of glyphosate-based herbicides in public spaces in the fall of 2017. The public works department warned residents that the change might mean more weeds, but complaints still rolled in.

City Council member Dan Carson put it bluntly at a public meeting in 2020 when he complained about the medians on city roads: “It looked horrible,” he said. “It looked absolutely horrible.”

Davis decided to stop using glyphosate, one of the world’s most widely used herbicides, over concerns that it could be harmful to human health. Instead, workers pull weeds, suffocate them under plastic sheets, steam them with hot water, or burn them with torches. Those methods are more work, adding $400,000 to the city’s annual budget.

Gardeners in the US will soon face a similar challenge. Earlier this year, Bayer announced it would remove glyphosate from lawn and garden versions of its popular weed killer Roundup in the US by 2023. The company plans to create several new Roundup formulations with other, existing active ingredients. Bayer hasn’t announced what will replace glyphosate, but it will be difficult to find other chemicals that match glyphosate’s weed-killing firepower while maintaining its relatively low environmental and human health risks.

Bayer acquired the Missouri-based crop science company Monsanto in 2018 for $66 billion. That gave Bayer the Roundup brand but also a heap of legal liabilities. By the beginning of 2020, the company was facing about 125,000 court cases claiming Roundup caused cancer or other injuries. In June 2020, Bayer announced it would settle a large chunk of those lawsuits for nearly $10 billion.

During a conference call in July, Bayer CEO Werner Baumann emphasized that the company decided to move away from glyphosate exclusively to avoid further litigation, not because of any concern about safety.

Bayer will continue using glyphosate in its agricultural products. More than 90% of the glyphosate lawsuits come from home gardeners, though sales of agricultural products dwarf lawn and garden sales.

Bayer’s plan for dealing with the lawsuits stresses that regulatory agencies in Australia, Canada, Europe, Japan, the US, and other countries have all concluded that glyphosate is safe to use and unlikely to cause cancer. The only outlier is the International Agency for Research on Cancer, part of the World Health Organization, which warned in 2015 that glyphosate likely poses a cancer risk.

Bayer will choose active ingredients for the lawn and garden market that kill a broad spectrum of plants, “consistent with the expectations of our customers,” the company said in a statement.

No matter what the active ingredients are, the company will keep using the Roundup brand name. Glyphosate is long off patent, and other companies make glyphosate-based herbicides for the lawn and garden market. Baumann said on the call that the company doesn’t expect the brand to lose any traction after the switch. Bayer didn’t answer specific questions for this story and did not make anyone available for an interview.

While Bayer remains tight lipped about possible alternatives, there are a few clues. Austria and Belgium have already banned the use of glyphosate for private gardens. In those countries and several other European markets, Bayer sells Roundup formulations with either pelargonic acid, which is made from natural fats, or acetic acid, a component of vinegar.

Michael Braverman helps companies navigate the herbicide registration process at the IR-4 Project, which is funded by the US Department of Agriculture to identify and register new pesticides for specialty crops. Braverman, who has received research funding from Bayer but isn’t working on the Roundup reformulation, says the European products would give Bayer a head start in the US. The company could likely reuse much of the data for registration in the US.

Acetic acid and pelargonic acid are both contact herbicides that burn any vegetation they touch. Braverman says pelargonic acid could be a good replacement, partly because it’s cheap. Bayer includes small amounts of pelargonic acid in some existing US Roundup formulations, which means the company has done the regulatory legwork to get it approved as an active ingredient.

“You would need a higher concentration if it’s by itself,” Braverman says.

The US Environmental Protection Agency considers pelargonic acid and acetic acid biopesticides because they occur naturally. That would open the door to marketing new formulations of Roundup as more natural. But Guy Abrahams, a marketing consultant who worked on a Roundup marketing campaign in the early 2000s, says he would tell Bayer to continue focusing on existing customers, who think of Roundup as a heavy-duty product.

“If you’ve got a weed killer, it’s about performance,” he says. “What they need to lean into is that it’s good at killing. . . . I’d advise them not to position this as less kill-y.”

And biopesticides like pelargonic acid and acetic acid don’t kill weeds as well as glyphosate, according to Steve Duke, a weed scientist at the University of Mississippi. Even many conventional pesticides can’t match glyphosate’s effectiveness.

“It’s a pretty unique herbicide,” he says. “There’s no other compound out there that’s going to have the same properties.”

While many herbicides target specific groups of plants, glyphosate affects nearly all plants by disrupting a process that produces amino acids they need to survive. Glyphosate is also a systemic herbicide, meaning it is transported throughout the plant. As long as the dose is sufficient, it slowly kills every part of a plant, including the roots, rather than just the parts the spray touches.

The herbicide 2,4-D is systemic like glyphosate, but it kills only broad-leaved plants. Glufosinate can kill all plants but only damages tissue it touches. Braverman says pelargonic acid and acetic act quickly but aren’t as effective against older, well-established weeds.

Replacing glyphosate could prove to be the gardening equivalent of subbing a bench player for Michael Jordan. No one chemical can play defense, grab rebounds, and dunk. Duke says Bayer may have to combine multiple active ingredients to equal glyphosate’s weed-killing power.

“There are a lot of smart people at Bayer, so I’m sure they’ll come up with something,” Duke says. “But I doubt it’s going to have the overall utility that glyphosate has.”

Glyphosate is so effective that before Davis, California, banned it, the city’s public works department hadn’t really considered using other chemicals.

After the ban, a handful of areas were too difficult to clear manually, so the city had to find a new herbicide, according to public works director Stan Gryczko. After evaluating the options with an outside consultant, the city determined that glufosinate was the safest alternative.

However, the World Health Organization’s chemical safety program recommends classifying glufosinate as a little bit riskier than glyphosate, which is categorized as slightly hazardous. Similarly, the EPA’s recommended safety limit for glufosinate residue in drinking water is lower than the limit for glyphosate.

“It’s an ongoing challenge to find what is least toxic when you have to go to a chemical application,” Gryczko says.

From an environmental health perspective, glyphosate is considered relatively safe compared with other herbicides, according to Ryan Prosser, an ecotoxicologist at the University of Guelph. Like most herbicides, it can kill natural vegetation, but it’s only mildly toxic to animals, partially because the amino acid pathway it targets doesn’t exist in animals.

A 2018EPA environmental assessment came to a similar conclusion. It found that drifting glyphosate can kill plants next to agricultural fields and slow the growth of birds. In some cases, it can affect mammals’ growth and reproduction.

Prosser says glyphosate binds with soil particles, limiting the risk that it will pollute rivers and streams. He detects other, more water-soluble herbicides like 2,4-D, atrazine, and metolachlor in water more frequently.

Results from the EPA’s ECOTOXicology Knowledgebase toxicity database show that glyphosate and pelargonic acid are about equally toxic to rainbow trout, a common test species. Prosser says neither herbicide presents a high risk for rainbow trout or other aquatic animals, in line with the EPA’s assessment. “The general public feels that . . . the natural has got to be less toxic, less dangerous than the synthetic,” he says. “That’s not always the case.”

The picture is less clear when it comes to human health. That’s partially because the science around the safety of glyphosate has become a mud-slinging contest. Pesticide skeptics criticize industry-supported studies that consistently find glyphosate to be safe, while Monsanto waged a public relations offensive against scientists that questioned those conclusions.

The most recent assessment of glyphosate’s impact on human health by the EPA, published in 2018, found no risks of concern for human health and no evidence that glyphosate causes cancer in humans when used properly.

Anneclaire De Roos, an epidemiologist at Drexel University who has studied the long-term health effects of pesticides, says the epidemiological studies on glyphosate are a bit murky, sometimes finding a link to cancer and sometimes not.

She’s not convinced it causes cancer but says the combination of epidemiological results and concerning data from animal studies provides reasons to be skeptical of Bayer’s framing that glyphosate is innocuous. “Clearly, it’s doing more than causing irritation or cell damage,” De Roos says. “It’s not a benign chemical.”

But neither are most alternatives. While not conclusive, she says, some evidence points toward a link between cancer and phenoxyacetic herbicides like 2,4-D, the most widely used conventional herbicide for home gardeners in 2012, according to a list from the EPA.

The EPA doesn’t consider 2,4-D carcinogenic but warns that pendimethalin, also on the list of common herbicides, might be. Other common, conventional pesticides also pose their own health risks. Mecoprop and MCPA can cause severe eye irritation. In comparison, glyphosate only causes mild skin and eye irritation. Switching to other conventional herbicides after Bayer removes glyphosate from Roundup may not be a win for human health.

De Roos says she thinks removing glyphosate from home gardening products is a good idea. Farmers benefit enormously from glyphosate. Many grow crops that have been genetically modified to tolerate Roundup, making weed control easier and saving huge amounts of money every year. It’s harder to make a case for the societal benefit of tidy gardens.

“Everything needs to be weighed in terms of risk-benefit, including economics,” she says. “This is not a situation where you really need to kill these weeds. It’s just for your aesthetic benefit.”

Back in California, the Davis City Council made the same judgment. Ditching glyphosate made the medians a little scruffier, but council member Will Arnold said that’s a trade-off that people in Davis can live with.

“There might just be more weeds, and that’s not the worst thing in the world,” he said at a 2020 City Council meeting. “I don’t mind if there’s a few more weeds if that means we’re not spraying chemicals all over town.”