Glyphosate’s Rise to Top Weedkiller: A 1997 Account

What Is the 1997 Glyphosate Monograph?

It is a 653-page review of a single herbicide, published by the American Chemical Society in 1997 as ACS Monograph 189 (Franz et al., 1997). The authors were John Franz, Michael Mao and James Sikorski. Besides xv pages of front matter, the volume carries eight pages of plates, a bibliography and an index (Franz et al., 1997).

Franz is the reason the book carries weight. He joined Monsanto in 1955, discovered the glyphosate class of herbicides in 1970 and retired in 1991, six years before the book came out; the National Inventors Hall of Fame inducted him in 2007 (National Inventors Hall of Fame, 2026).

Franz found a use for the molecule rather than the molecule itself. IARC notes that glyphosate was first synthesised in 1950 as a possible pharmaceutical, and its herbicidal activity emerged only when it was made again and tested in 1970 (International Agency for Research on Cancer, 2017).

The publisher presents the book as a comprehensive review of the herbicide’s history and properties, chemistry and biology, formulation and technology, enzymology and structure–activity relationships (Franz et al., 1997). It adds syntheses of hundreds of analogues and derivatives and an account of how glyphosate acts on its target enzyme (Franz et al., 1997). The same description praises the herbicide’s environmental properties, soil inactivity and low toxicity (Franz et al., 1997). Those are the publisher’s words about a book led by the chemist who found its herbicidal use, not an independent assessment.

How Does Glyphosate Kill Plants?

Glyphosate kills plants by blocking EPSP synthase, an enzyme of the shikimate pathway that plants use to make aromatic amino acids (International Agency for Research on Cancer, 2017). According to IARC, it competitively inhibits this enzyme, which is not present in mammalian cells (International Agency for Research on Cancer, 2017).

The target was pinned down in 1980, a decade after the herbicidal effect was found. Steinrücken and Amrhein reported that year that glyphosate is a potent inhibitor of 5-enolpyruvylshikimic acid-3-phosphate synthase, the enzyme’s full name (Steinrücken & Amrhein, 1980). Writing in 2008, Duke and Powles noted that glyphosate is the only herbicide that targets this enzyme (Duke & Powles, 2008).

What the monograph covers

The 1997 book builds on that biochemistry. Its publisher says it clarifies the molecular mode of action on EPSP synthase and also covers uptake and transport in plants, metabolism in soil and plants, and formulation (Franz et al., 1997). The blurb opens by calling glyphosate a popular post-emergent herbicide for perennial weeds (Franz et al., 1997).

From a laboratory find to a global product

Commercial sales began in 1974, when the isopropylamine, sodium and ammonium salts were introduced; a trimesium salt followed in Spain in 1989 (International Agency for Research on Cancer, 2017). Duke and Powles later wrote that glyphosate grew into the world’s dominant herbicide after that 1974 launch (Duke & Powles, 2008). By 2010 it was registered in at least 130 countries, and more than 750 products containing it were reportedly on sale in the USA alone (International Agency for Research on Cancer, 2017).

An enzyme missing from mammalian cells gives glyphosate a clear biochemical difference between its effect on plants and on people (International Agency for Research on Cancer, 2017). That difference is not a safety verdict in itself. Regulators still assess residues in food, wildlife and cancer data separately, and their conclusions differ, as later sections show (European Commission, 2023; European Food Safety Authority, 2023).

Why Did Glyphosate Use Surge After 1997?

Duke and Powles judged glyphosate-resistant crops perhaps the most important reason for the herbicide’s success, alongside a sharp fall in its price once it became a generic compound (Duke & Powles, 2008). IARC dates the first glyphosate-tolerant genetically modified crops to 1996 (International Agency for Research on Cancer, 2017). It says the original patent protection expired outside the USA in 1991 and within the USA in 2000 (International Agency for Research on Cancer, 2017).

Herbicide-tolerant seed then spread quickly across American farms. The share of US soybean acres planted with it rose from 17% in 1997 to 68% in 2001 and reached 96% in 2024 (Economic Research Service, US Department of Agriculture, 2025). In 2025 herbicide-tolerant varieties covered 93% of upland cotton, and the figure for maize is about 92% (Economic Research Service, US Department of Agriculture, 2025).

An analysis by Benbrook estimated that total global glyphosate use rose more than 12-fold, from about 67 million kg in 1995 to 826 million kg in 2014 (Benbrook, 2016). Agricultural use alone rose 14.6-fold over the same years. By 2012, genetically engineered herbicide-tolerant crops accounted for 56% of global agricultural use (Benbrook, 2016). In the United States, agricultural use grew roughly 300-fold between 1974 and 2014 (Benbrook, 2016).

These numbers need care: Benbrook built the global series from industry production figures, treats parts of it as projections and disclosed funding from organic food companies (Benbrook, 2016).

How Did Weeds Adapt to Glyphosate?

Weeds adapted by evolving resistance. As of September 2026, the International Herbicide-Resistant Weed Database lists 62 weed species resistant to inhibitors of EPSP synthase, the mode of action glyphosate uses (International Herbicide-Resistant Weed Database, 2026). The earliest entry in its table is rigid ryegrass (Lolium rigidum) from Victoria, Australia, in 1996 (International Herbicide-Resistant Weed Database, 2026).

That first report came a year before the monograph appeared (Franz et al., 1997; International Herbicide-Resistant Weed Database, 2026). The publisher’s description of the book dwells on chemistry, biology and environmental behaviour rather than on resistance (Franz et al., 1997). A decade later the picture looked different. Duke and Powles praised glyphosate as a virtually ideal herbicide but warned that its use was now threatened by resistant weeds (Duke & Powles, 2008).

Reading the resistance numbers

The count of 62 refers to species, not to individual cases in different countries or crops, and the database is live, so the total changes as new reports are confirmed (International Herbicide-Resistant Weed Database, 2026).

The farm context helps explain why the number matters. With 96% of US soybean acres planted to herbicide-tolerant seed in 2024, such varieties dominate the main US field crops, and they are bred to tolerate herbicides such as glyphosate, glufosinate and dicamba (Economic Research Service, US Department of Agriculture, 2025). Duke and Powles discussed glyphosate-resistant crops, introduced in 1996, alongside the threat that resistant weeds pose to the herbicide’s use (Duke & Powles, 2008).

Does Glyphosate Cause Cancer, and Why Do Agencies Disagree?

Agencies disagree. In 2015 IARC classified glyphosate as probably carcinogenic to humans (Group 2A), while the US EPA judged it not likely to be carcinogenic (International Agency for Research on Cancer, 2017; US Environmental Protection Agency, 2026). An EU risk committee found it does not meet the criteria for classification as a carcinogen (European Commission, 2023).

The IARC working group met in Lyon on 3–10 March 2015, and the full volume followed in 2017 (International Agency for Research on Cancer, 2017). It found limited evidence in humans, based on a positive association with non-Hodgkin lymphoma, and sufficient evidence in experimental animals (International Agency for Research on Cancer, 2017). It also judged the mechanistic evidence strong, including for genotoxicity and oxidative stress (International Agency for Research on Cancer, 2017).

EPA concluded in 2017 that glyphosate is not likely to be carcinogenic to humans and attributes the gap with IARC to differences in scope and method (US Environmental Protection Agency, 2026). In 2022 an appeals court vacated the human-health portion of its 2020 interim decision, and EPA withdrew that decision (US Environmental Protection Agency, 2026).

In Europe, the Committee for Risk Assessment of the European Chemicals Agency found in 2022 that glyphosate does not meet the criteria for classification as carcinogenic (European Commission, 2023), and EFSA reported in 2023 that it identified no critical areas of concern (European Food Safety Authority, 2023).

What Is Glyphosate’s Legal Status in 2026?

Glyphosate remains approved in the EU until 15 December 2033 under Implementing Regulation (EU) 2023/2660 (European Commission, 2023). Member States reached no qualified majority either way, in the standing committee or on appeal, so the Commission adopted the renewal itself (European Commission, 2023). Any application to renew beyond 2033 is due by 15 December 2030 (European Commission, 2026).

Conditions attached to the EU renewal

Only uses as a herbicide may be authorised, and spraying to desiccate crops before harvest is banned (European Commission, 2023). By default, professional field spraying needs an unsprayed in-field buffer strip of 5 to 10 m and nozzles that cut drift by at least 75% (European Commission, 2023). Equivalent measures may replace them, and they can be dropped when a product’s risk assessment shows no need (European Commission, 2023). The regulation also notes that indirect effects on biodiversity could not be excluded (European Commission, 2023).

Courts and settlements in the United States

The US Supreme Court decided Monsanto Co. v. Durnell on 25 June 2026 (Supreme Court of the United States, 2026). By seven votes to two, it held that federal pesticide law expressly preempts a state failure-to-warn claim that would require a cancer warning on Roundup’s label (Supreme Court of the United States, 2026). The case turned on labelling where EPA had not required such a warning, not on whether glyphosate causes cancer (Supreme Court of the United States, 2026).

Reuters reported that Bayer faces about 65,000 claims from people who say they developed cancer after using Roundup, which Bayer denies, and has proposed a $7.25 billion class settlement in a Missouri state court (Knauth, 2026).

How Should the 1997 Book Be Read Today?

The book is best read as a technical record of glyphosate’s chemistry and biochemistry at a turning point, led by a scientist from the company behind Roundup (Franz et al., 1997; National Inventors Hall of Fame, 2026; Supreme Court of the United States, 2026). Its technical core, as the publisher describes it, is synthesis, structure–activity work on hundreds of analogues, formulation and the target enzyme (Franz et al., 1997).

The biochemistry at its centre has lasted. EPSP synthase, identified as glyphosate’s target in 1980, is still the enzyme IARC named as its target in 2015 (Steinrücken & Amrhein, 1980; International Agency for Research on Cancer, 2017). For readers interested in how herbicides are designed, the book’s subject matter remains relevant (Franz et al., 1997; Duke & Powles, 2008). It was also written three years before the original US patent protection on glyphosate expired, in 2000 (International Agency for Research on Cancer, 2017).

A monograph led by the man who found glyphosate’s weedkilling power captures how the molecule works, but was written before its success showed its costs.

Its framing has aged less well. The publisher’s praise of low toxicity and soil inactivity came before IARC’s 2015 classification and before EFSA’s first-tier assessment flagged a high long-term risk to mammals in many representative uses (Franz et al., 1997; International Agency for Research on Cancer, 2017; European Food Safety Authority, 2023). It also came before resistance spread to 62 species and before the EU tied renewal to buffer strips and a desiccation ban (International Herbicide-Resistant Weed Database, 2026; European Commission, 2023).

Readers should also weigh who wrote it: Franz spent his career at Monsanto (National Inventors Hall of Fame, 2026). For the current science, the regulatory documents cited here are the better starting point (European Commission, 2023; European Food Safety Authority, 2023; US Environmental Protection Agency, 2026).

Frequently asked questions

Tobias Mardle — author

Tobias Mardle is an author with a background in agricultural engineering. A graduate in Agricultural Engineering, his earlier work focused on explaining farm machinery, guidance systems and the use of field data to growers and agricultural advisers. At Cabdire...