Readers respond to an Opinion guest essay about the common weedkiller Roundup.
Re "MAHA Is Focused on the Wrong Pesticide," by Michael Grunwald (Opinion guest essay, Oct. 3):
"There is no Roundup crisis," Mr. Grunwald writes. But there is, and the crisis is epistemological: The scientific record has been skewed to the point that a credible risk-benefit analysis of glyphosate cannot be conducted with confidence.
One telling case is a glyphosate safety review published in the journal Regulatory Toxicology and Pharmacology in 2000. Litigation documents released in 2017 revealed that it was conceived and drafted by Monsanto staff members, yet it circulated as an independent review. Twenty-five years on, it still anchors the conversation: heavily cited, invoked in policy debates and embedded in Wikipedia and, by extension, A.I. models -- shaping how the public encounters "the science."
Against that backdrop, proposing the development of alternative herbicides simply doubles down on a contaminated pipeline. The first step must be to repair the knowledge base with transparent authorship and funding, independent replication and regulatory re-review that discounts conflicted work. Fix the pipeline, and only then can "better" truly mean "safer."
Alexander A. Kaurov
Naomi Oreskes
Cambridge, Mass.
The writers are the authors of a paper on the 2000 glyphosate safety review cited in this letter.
To the Editor:
Michael Grunwald expounds on the benefits of the herbicide Roundup without mentioning the detrimental environmental effects of its active ingredient, glyphosate. He correctly points out that Roundup is an effective weedkiller, but fails to mention its impact on milkweed, an essential component of the monarch butterfly's life cycle, and a major factor in the species' demise across North America.
Of course, the deforestation of the monarchs' overwintering habitat of the oyamel forests in Michoacan, Mexico, is another serious threat. We need to start recognizing that milkweed and other flowering wildflowers are not noxious weeds but actually beneficial plants for the beloved monarchs and myriad other insects.
Brian Houseal
Brunswick, Maine
The writer facilitated the trinational North American Monarch Conservation Plan on behalf of the NAFTA Commission on Environmental Cooperation.
To the Editor:
Michael Grunwald's defense of glyphosate misses the forest for the food crops. The most dangerous toxicity of glyphosate, the main active ingredient in Roundup, is ecological. When it is sprayed on crop fields it enters the environment, where it wipes out nontarget plants that provide critical habitat for birds, butterflies, reptiles and amphibians.
The now-endangered status of monarch butterflies is due in large part to Roundup's killing all the milkweed that formerly grew at the margins of agricultural fields, and that is critical to monarch egg-laying and caterpillar growth.
There are many more examples; please do not restrict discussion of health to humans when there is a whole planet full of life that we are actively poisoning with chemicals like glyphosate.
Liza Ryan
San Rafael, Calif.
To the Editor:
I am a board-certified pediatrician. In 2023, the American Academy of Pediatrics published a clinical report that didn't condemn genetic engineering but cautioned that its main use, engineering crops to survive repeated sprayings of Roundup, means the herbicide ends up in our food. The report cited studies linking glyphosate exposure to cancers and endocrine disruption.
Michael Grunwald notes in his essay that glyphosate blocks an enzyme that is found in plants, but is "nonexistent in animals," and he states that it "can kill weeds without harming anything else." He overlooks, however, the fact that this enzyme exists in the bacteria that make up our microbiome.
Glyphosate's antimicrobial effect can upset the balance of the trillions of beneficial bacteria that live in and on our bodies. Bacterial imbalances are increasingly linked to poor health.
Glyphosate use has surged over the last three decades, while our nation's health has deteriorated. Many peer-reviewed studies now document the adverse health effects of glyphosate-based herbicides. That evidence suggests that Roundup is far from completely safe.
Lee A. Evslin
Kapaa, Hawaii
To the Editor:
Michael Grunwald's defense of glyphosate is less science than spin. He frames the debate as wellness warriors versus regulators, but sidesteps a deeper truth: Science in agriculture is not neutral. It has long been politicized by the corporate sector. Regulators lean on industry-funded studies while dismissing independent, peer-reviewed evidence that threatens profits.
Mexico's own national science dossier on glyphosate and genetically modified corn is rigorous, peer-reviewed and alarming, and documented real risks to health and biodiversity. Instead of reckoning with that research, the United States and agribusiness lobby waved it away in favor of science for hire.
Both the MAHA movement and corporate apologists erase the real crisis: a food system captive to agribusiness, where what counts as sound science is dictated by those with the most to lose.
If we cannot tell the difference between independent science and corporate propaganda, then we've already surrendered the future of our food -- and our health -- to industry.
Loren Cardeli
Mexico City
To the Editor:
Michael Grunwald's piece essentially parrots chemical companies' talking points about Roundup's health effects and misleads readers about its importance for the future of food. Roundup may be largely safe for consumers, but there are enough questions about its health effects on farmers and pesticide applicators that Roundup's manufacturer, Bayer, has paid out more than $10 billion to settle lawsuits for human health effects.
Bayer sells most Roundup as a weedkiller for genetically modified corn and soybean crops that produce vast amounts of biofuels, cattle feed and ultraprocessed foods. That is not what we need to fix a food system that leaves roughly two billion people around the world with food insecurity, including one in seven Americans, many of them hungry or malnourished, and that contributes to rates of diabetes and obesity that cost trillions globally. What we do need is a food system that nourishes people without destroying the planet.
Agroecology, an approach to agriculture that integrates social and ecological principles to create sustainable farming and food systems, provides a framework for getting us there. In a debate with Mr. Grunwald in April, I explained how agroecology interweaves multiple fields of science with the wisdom of farmers past and present. We have decades of evidence that it is working all over the world. What we haven't had is the political will to make it the foundation of our food system.
Tim Bowles
Barcelona, Spain
The writer is a professor of agroecology at the University of California, Berkeley.