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California Prop 65, glyphosate and soybeans: What farmers need to know

Article cover photo
The Iowa Soybean Association assembled the following answers to frequently-asked-questions about Prop 65, the association’s motivation in joining as a co-plaintiff in the lawsuit, the science behind glyphosate, and the impact on agriculture should the Prop 65 listing stand. (Photo: Joseph Murphy/Iowa Soybean Association)

By Aaron Putze, APR

The Iowa Soybean Association (ISA) Board unanimously approved joining as a co-plaintiff in legal action challenging California’s Proposition (Prop) 65 and the listing of glyphosate as carcinogenic.

On Wednesday (Nov. 15), the lawsuit was filed. ISA joined other state and national agricultural groups as a plaintiff in the legal challenge against the California Office of Environmental Health Hazard Assessment (OEHHA). Specifically, the suit disputes the state’s inaccurate classification of glyphosate under Prop 65.

The ISA has assembled the following answers to frequently-asked-questions about the lawsuit, Prop 65, the association’s motivation in joining as a co-plaintiff in the lawsuit, the science behind glyphosate, the product’s importance to agriculture and the impact on agriculture should the Prop 65 listing stand.

What is the lawsuit?

Under California Prop 65, businesses must warn Californians about the presence of chemicals “known to the State of California to cause cancer.” California’s Office of Environmental Health and Hazard Assessment (OEHHA) has issued a notice that glyphosate will be added to the list of chemicals subject to Prop 65.

The OEHHA’s action was prompted after the France-based International Agency for Research on Cancer (IARC) reported that glyphosate is probably carcinogenic. This report automatically triggered California’s listing mechanism under Prop 65. 

Plaintiffs, including the ISA, seek declaratory and injunctive relief against the OEHHA to prevent it from mandating false, misleading and highly controversial cancer warnings concerning the herbicide.

What is the lawsuit challenging?

The arbitrary listing by the OEHHA of glyphosate as a carcinogen as compelled by Prop 65 violates the First Amendment of the U.S. Constitution because it compels the plaintiffs in the case to make false, misleading, and highly controversial statements about their products. The listing also conflicts with, and is preempted by, the U.S. Federal Food, Drug and Cosmetic Act (FDCA). The FDCA regulates the presence of herbicides on food and establishes scientifically-set safe food tolerance levels for herbicide residues in food and forbids the misbranding of food products with any false or misleading information.

What is Prop 65?

In 1986, the California voters, by initiative, enacted the Safe Drinking Water and Toxic Enforcement Act of 1986—commonly known as Prop 65.  In general, Prop 65 prohibits businesses from both exposing California residents to chemicals known to the state to cause cancer without providing required warnings, and from knowingly discharging a chemical known to the state to cause cancer into the environment where the chemical passes or will probably pass into a source of drinking water. Prop 65 provides a number of mechanisms by which OEHHA is directed to perform this listing function and, as relevant here, provides that OEHHA’s “list shall include at a minimum those substances identified by reference in The California Labor Code. The Labor Code in turn references “[s]ubstances listed as human carcinogens by the International Agency for Research on Cancer.” 

Why is the Iowa Soybean Association joining as a co-plaintiff?

The ISA board of directors unanimously approved joining as a co-plaintiff in the legal challenge to California’s Prop 65 and the listing of glyphosate as a carcinogen. The loss of glyphosate because of a France-based, non-scientific organization making an arbitrary determination that negatively impacts consumers and food producers sets a dangerous precedent. It would also devastate farmers who rely on glyphosate as a critical weed management tool.

Who are the other plaintiffs?

The plaintiffs include the National Association of Wheat Growers, National Corn Growers Association, United States Durum Growers Association, Agri-Turf Distributing, LLC, Missouri Farm Bureau, South Dakota Agri-Business Association, Western Plant Health Association, North Dakota Grain Growers Association, Missouri Chamber of Commerce and Industry, Monsanto Company, Associated Industries of Missouri and the Agribusiness Association of Iowa.

What’s the potential impact on soybean farmers if OEHHA’s designation stands?

If the OEHHA’s action proceeds unimpeded, the ripple effect would quickly and negatively impact farmers in Iowa and wherever soybeans are grown in the United States. Labeling glyphosate a carcinogen would likely require either the elimination of glyphosate altogether or, at the very least, segregation (somehow) of soybeans produced in fields where weeds were treated with glyphosate. Farmers and landowners will be severely impacted by either the elimination of the weed management tool or the creation of an identity preserved system. Both scenarios would increase production costs substantially and threaten the viability of the U.S. soybean crop due to intensified weed pressures (Iowa soybean farmers are expected to harvest nearly 560 million bushels of soybeans this fall with a market value of nearly $5.3 billion).

Is the science around glyphosate controversial?

The herbicide is approved by the federal government for use in more than 250 agricultural crop applications in all U.S. states. Subject to significant scientific review by the federal government repeatedly for multiple decades, glyphosate is regarded as one of the safest herbicides ever developed and is widely recognized as non-carcinogenic. The U.S. Environmental Protection Agency has emphatically reaffirmed its 1991 classification of glyphosate as a Group 3 oncogen – one that shows evidence of non-carcinogenicity for humans – based on the lack of the convincing evidence of carcinogenicity in adequate studies.

How and where is glyphosate used?

Glyphosate is safely used on most corn, soybean and canola crops grown in the United States and Canada. It’s also used in conjunction with cultivation of wheat, beans, peas and other crops in many locations including almond, citrus, cotton and other crops in California. Finally, glyphosate is used by municipalities to control vegetation in utility right-of-ways, along roadsides and railways, in aquatic environments, in residential home and garden settings and to reduce the risk associated with the rapid spread of wildfires.

What benefits are there to using glyphosate?

In addition to all-important weed management, glyphosate allows farmers to control weeds with minimal tilling of soil, thereby conserving valuable topsoil, reducing soil movement into streams and other surface water, retaining soil moisture and reducing fuel and energy use.

Does the IARC determination have merit?

IARC is an international organization based in Lyon, France.  It is not a regulator.  Instead, IARC prepares so-called informational “Monographs” regarding the possibility that everyday products and substances may be carcinogenic.  IARC is perhaps most famous (or infamous) for its conclusions that substances like coffee, aloe vera, pickled vegetables, and food exposed to “high temperatures”—such as French fries—are probably or possibly carcinogenic.  See, e.g., Law360, Starbucks’ ‘Junk Science’ Downplays Cancer Risk (Apr. 9, 2015) (noting Starbucks’ disagreement with “junk science”).

The determination by IARC that glyphosate is probably carcinogenic is counter to the conclusion of every global regulatory body that has examined the issue over the past 40 years, including the OEHHA itself (the OEHHA has previously concluded that glyphosate is not carcinogenic). It’s also important to note that OEHHA’s designation of glyphosate as a chemical “known” to cause cancer is based solely on IARC’s conclusion that glyphosate is “probably carcinogenic.” Not only does the scientific community disagree with IARC’s conclusion, IARC’s internal process for reviewing glyphosate has also been roundly criticized.


For media inquiries, please contact Katie James, ISA Public Relations Manager at or Aaron Putze, ISA Communications Director at

For permission to republish articles or to request high-res photos contact Aaron Putze at Iowa Soybean Association | 1255 SW Prairie Trail Pkwy | Ankeny | IA | 50023 | US

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