sciences & medical health

ISIS Report 08/11/12

Study Confirms GM crops lead to increased Pesticide Use

GM technologies have led to a 7% increase in pesticide use Dr Eva Sirinathsinghji

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A new peer-reviewed study has blown away the persistent claims made by agritech corporations that GM crops are beneficial to both the environment and human health by reducing pesticide use.

The study, led by Professor Charles Benbrook at Washington State University, US was published in the peer-reviewed journal Environmental Sciences Europe and shows that overall pesticide use in the US has gone up by 7 % from 1996 to 2011. Most crucially, this rise comes as a direct result of genetically modified (GM) crop cultivation [1]. Herbicide-tolerant (HT) crops, mainly those tolerant to Monsanto’s glyphosate-based herbicide Roundup, have increased herbicide use by 239 million kilograms, while GM crops expressing the insecticidal toxins Bacillus thuringiensis(Bt) have reduced  insecticide use by 59 million kilograms. But the emergence of Bt-resistant pests means that insecticide use is expected to rise in the near future.

Drawing upon publicly available USDA data, the study applied a model to quantify the impacts of the 6 major GM crops on the kilograms of pesticides applied per hectare and across all GM hectares. The 6 crops were glyphosate-tolerant corn, soybean, and cotton; Bt corn targeting the European corn borer; Bt corn targeting corn rootworms; and Bt cotton targeting Lepidopteron insects. Non-GM and GM crop data were compared to assess the impact GM crops have on pesticide application rates. Of the extra 239 million kgs (527 million pounds) of herbicide applied in the 1996–2011 period, soybean accounted for 70 % of the total increase across the three HT crops, mostly from reliance on glyphosate. Furthermore, the data show that although pesticide use decreased from 1996-2002, it then increased since 2002 as the result of two major factors.

The first is a reduction of herbicides applied to non-HT crops, which can be explained by the increasing progress made by the pesticide industry in discovering more potent herbicidal active ingredients effective at progressively lower levels. Between 1996 and 2006, the number of registered soybean herbicides applied at levels below 0.11 kg/ha increased from nine to 17. As a result, the amount of herbicides applied to conventional crops has steadily fallen since 1996. In contrast, glyphosate is a relatively high-dose herbicide usually applied at between 0.67 to 0.9 kg/ha.

The second major factor for the increase in pesticide use due to GM crops is the spread of glyphosate-resistant weeds. That, the authors suggest, is by far the most important factor in driving up herbicide use over the last decade.

Since the emergence of glyphosate-resistant ryegrass in Australia in 1996, there has been an additional 22 species of resistant species that have forced some farmers to abandon their crops due to the severity and resilience of the so-called “super-weeds”  (see [2] Monsanto Defeated by Roundup-Resistant Weeds SiS 53). The majority of resistant species have been documented since 2005, reflecting the extreme selection pressure placed on plants as a result of wide-scale glyphosate application.  

Pest resistance to Bt toxins has only been recently documented and does not therefore parallel the impacts seen with glyphosate-resistant weeds. However, with populations of corn rootworm resistant to Cry3Bb1 toxin [3] (see [4] Bt Resistant Rootworm Spreads, SiS 52), reduced insecticide use is in jeopardy, particularly when companies advise farmers to revert back to soil-based insecticides as a management tool. Not only is this increasing the pesticide burden, but completely negates the purpose of Bt crops in the first place.

An important point brought up by the study is the notion of counting Bt toxins produced by GM crops as “insecticides applied”.  When Bt toxins are applied exogenously, they would be included in insecticide use counts. Although there are differences between exogenous Bt and that produced by GM plants, the environmental burden may indeed be the same. Further, GM Bt crops increases the likelihood of ingestion of the insecticide by animals and humans, posing more risk than Bt sprays which can be washed off and break down in sunlight. Bt crops have been associated with health problems including respiratory problems, allergies and immunogenicity, internal organ damage, as well as skin and eye damage (see [5] Bt Crops, Failures and Hazards, SiS 53).

With the proposed deregulation of GM crops tolerant to the herbicide 2.4-D, this herbicide was projected to increase an estimated 30-fold from 2010 levels if 55 % of HT corn is 2,4-D resistant coupled with 2.3 applications at 0.94 kg/ha on average. The herbicide has been linked to many health problems including congenital birth defects, so this dramatic rise in 2,4-D application would be a huge public health concern.

Although few studies have attempted to calculate pesticide application levels, those living and working in pesticide-use zones are more than aware of these facts. However the GM industry is a well-polished propaganda machine that endlessly distorts facts with misinformation and lies. The accumulation of peer-reviewed data however, is beginning to overpower the noise created by the industry. Now, we have data showing that pesticide use is on the rise. The health and environmental risks posed by glyphosate and Bt toxins have been documented in over 100 peer-reviewed studies (see [5, 6] Why Glyphosate Should be Banned, SiS 56). It is becoming ever clearer that these substances need to be removed from the market until proven safe to both people and the planet.


  1. Benbrook C. Impacts of genetically engineered crops on pesticide use in the U.S. - the first sixteen years.  Environmental Sciences Europe2012, 24,24 doi:10.1186/2190-4715-24-24
  2. Sirinathsinghji E. Monsanto Defeated By Roundup Resistant Weeds.Science in Society 53, 40-41, 2011.
  3. Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW. Field-evolved resistance to Bt maize by Western corn rootworm.PLoS One2010, 6, e22629.
  4. Sirinathsinghji E. Bt Resistant Rootworm Spreads. Science in Society 52, 34-36, 2012
  5. Sirinathsinghji E. Bt Crops Failures & Hazards.Science in Society 53, 44-45, 2012
  6. Sirinathsinghji E & Ho MW. Why Glyphosate Should be Banned Science in Society 56, to appear