How Does Glyphosate (Roundup) Herbicide Function?

Key Insights

Protecting crops from pests is a challenge for even the most skilled farmers. While the development of chemical pesticides has made this task easier, it has also created a new problem: finding a solution that keeps pests at bay without harming unintended targets.

Roundup (a trademark of Monsanto) and other herbicides containing glyphosate (its generic name) are among the most widely used weed killers in the U.S. These chemicals are utilized by farmers, foresters, gardeners, and biologists alike to manage invasive plant species.

Herbicides based on glyphosate share a common biochemical action – they block an enzyme known as EPSP synthase [source: Funke et al.]. This enzyme is crucial for plants to synthesize proteins necessary for growth, and without it, plants turn yellow and die over several days or weeks. Nearly all plants rely on this enzyme, so glyphosate is effective against most plant species.

Given that all plants require EPSP synthase for survival, why would farmers choose to use glyphosate? As the herbicide gained popularity, scientists developed genetically modified crops that could withstand it. By 2018, 91% of U.S. cotton, 94% of soybeans, and 90% of corn were "Roundup-Ready" varieties [source: USDA]. The premise was simple: the herbicide kills the weeds while leaving the crops intact.

In recent years, concerns have grown about consuming genetically modified foods. When glyphosate is added to the equation, many people have raised further questions regarding the safety of both the herbicide and the crops that are engineered to resist it.

While glyphosate is generally considered less toxic to humans than other herbicides, some experts raise concerns about its potential to disrupt endocrine function in people [source: U.S. National Institutes of Health]. Other animals, including frogs and fish, may also experience harmful effects.

Researchers investigating glyphosate have observed an increase in cases of Non-Hodgkin lymphoma, a cancer type, among individuals exposed to the chemical [source: Dixon]. The International Agency for Research on Cancer, part of the World Health Organization, declared in March 2015 that glyphosate is "probably carcinogenic to humans."

However, the news agency Reuters uncovered evidence suggesting that the IARC's report had omitted conclusions from some scientists stating that glyphosate was not linked to cancer in laboratory animals. In August 2019, the U.S. Environmental Protection Agency (EPA) declared it would not approve cancer warning labels for glyphosate.

The EPA stated that its review of long-term animal studies found no evidence suggesting glyphosate is toxic to the nervous or immune systems, nor does it appear to be a developmental or reproductive toxin. However, the agency acknowledged that glyphosate is typically mixed with other ingredients when applied and can cause skin and eye irritation [source: National Pesticide Information Center]. Some argue, however, that glyphosate is highly toxic to both animals and humans.

Nevertheless, the overuse of glyphosate has led to the emergence of glyphosate-resistant "superweeds" in agricultural fields. Potential solutions to this issue include using a variety of herbicides rather than relying on just one and further modifying crops to be resistant to multiple herbicides [source: Genetic Literacy Project, Wilkerson]. These solutions have faced criticism, while more eco-friendly approaches like using cover crops, crop rotation, and manual weed removal, though labor-intensive, are gaining traction.