Do GMO crops increase the use of pesticides?

By Eva Greenthal

April 29, 2021

It’s a polarizing question with no simple answer.

Pesticides—substances used to destroy or repel pests—are one of several pest management tools that farmers use to prevent crop loss and increase the efficiency of crop production. While they provide important benefits to farmers, chemical pesticides can pose varying levels of risk to humans and the environment depending on their properties and how they are used.

You may have seen scientists and advocates of different persuasions argue one way or another—either genetically engineered (GE) crops increase the use of pesticides, or GE crops decrease the use of pesticides.

The problem with these sweeping statements is that “pesticides” is a broad category that includes herbicides (pesticides used to destroy weeds), insecticides (pesticides used to repel insects), and more. Also, different GE crops are engineered with different traits and are designed to interact with specific herbicides or insecticides in different ways.

Crops engineered with herbicide tolerance allow farmers to spray those specific herbicides to kill the weeds around a plant, but enable the plant to survive. Crops engineered with insect resistance produce their own biological pesticides which are toxic to insects but (ideally) not to humans. The details matter. And so a case-by-case consideration of each product is necessary.

At Center for Science in the Public Interest (CSPI), we set out to answer the question of whether GE crops increase the use of pesticides, and dove into the weeds of the available data. Our new report, “In the Weeds: Understanding the Impact of GE Crops on Pesticide Use” identifies specific questions that need answering in order to assess the impact of these crops on agriculture’s chemical footprint, and begins to answer those questions.

We ask:

  • How has the adoption of insect-resistant crops impacted the use of insecticides?; and
  • How has the adoption of herbicide-tolerant crops impacted the use of herbicides?

Here are our topline findings:

  • The impacts of GE crops on pesticide use must be considered on a case-by-case basis: crop by crop and pesticide by pesticide, with particular attention to substitution effects and their implications for the net toxicity of pesticides applied on each crop.
  • There is no simple answer to whether the net impact of GE crops on pesticide use has been beneficial or adverse.
  • The debate over pesticide use and GE products should only apply to GE crops with traits related to pesticide use, not traits unrelated to pesticide use, such as non-browning apples and potatoes.
  • GE insect-resistant crops have been associated with a significant reduction in insecticide sprays across all crops engineered with traits for insect resistance.
  • The impact of GE herbicide-tolerant crops upon herbicide use depends on which crop, which trait, and which herbicide(s) one considers.
  • The first generation of herbicide tolerant crops were designed to withstand spraying of the herbicide glyphosate, which is relatively less toxic than most other chemical herbicides in common use.
  • Since glyphosate-tolerant crops became widely adopted in the early 1990s, use of glyphosate and overall herbicides has increased in corn, soybean, and cotton (as well as in non-GE crops like wheat and barley).
  • However, trends in herbicide use are better measured by changes in toxicity (volume X toxicity) rather than by volume alone, as adoption of herbicide-tolerant crops has changed the mix of herbicides used.
  • Acute (or short-term) toxicity of overall herbicide use after the introduction of GE crops decreased for all three major crops (corn, soybean, and cotton) and chronic (or long-term) toxicity of herbicides decreased by 78% in soybean, but increased by 7 percent in corn and by 91 percent in cotton.

Our report calls for caution in pesticide use going forward, noting recent trends that may threaten progress made with the adoption of GE crops. As we’ve seen in COVID, organisms have the ability to adapt to changing circumstances. While organisms can develop resistance to any pesticide (not just those associated with GE crops), the adoption of GE crops has in some cases accelerated the evolution of resistance. Weeds have developed resistance to herbicides use with GE herbicide-tolerant crops, and insects have developed resistance to the bioinsecticides produced by some GE insect-resistant crops.

To prevent the loss of the benefits identified above, integrated pest management practices must be implemented to mitigate these threats. Stacked trait products (which are GE products with multiple introduced genes providing multiple new traits) are increasingly common and represent a potentially promising approach to emerging weed and insect resistance, but could also lead to increased volume and toxicity of pesticide applications.

Finally, and perhaps most concerning, the latest herbicide-tolerant crops are designed for use with herbicides such as 2,4-D and Dicamba that are considerably more toxic than glyphosate. Their adoption and impact on net toxicity of herbicide applications must be closely monitored.

We invite you to learn more by reading our new report. The CSPI Biotechnology Project will continue to monitor the impact of agricultural biotechnology on human and environmental health, and to advocate for practices that protect the health and well-being of farmers and farmworkers, the environment and the public.

Eva Greenthal is a Senior Science Policy Associate whose work at CSPI focuses on food labeling, scientific integrity, biotechnology, and more. This article was originally published on the CSPI website.