5. GM crops – impacts on the farm and environment

Section at a glance

  • GM does not increase intrinsic yield. Some GM crops have lower yields than non-GM counterparts.
  • GM crops have increased pesticide use by 383 million pounds in the US in the first 13 years since their introduction.
  • The modest reduction in chemical insecticide sprays from GM Bt insecticidal crops is swamped by the large increase in herbicide use with GM herbicide-tolerant crops.
  • GM herbicide-tolerant crops have caused an over-reliance on a single herbicide, glyphosate, leading to the emergence of resistant superweeds and causing farmers to use more herbicides, including older toxic ones like dicamba and 2,4-D.
  • The GM companies’ solution to the glyphosate-resistant superweeds problem is stacked trait GM crops that tolerate applications of multiple herbicides – and mixtures of herbicides. Weed scientists warn that this will cause herbicide use to triple, foster multi-herbicide-resistant superweeds, and undermine sustainable farming.
  • Claims of environmental benefits from no-till of farming as used with GM herbicide-tolerant crops collapse once herbicide use is taken into account.
  • GM Bt crops do not eliminate insecticide use – they merely change the way in which insecticides are used. The plant itself becomes an insecticide.
  • GM Bt technology is being undermined by the spread of insect pests that are resistant to Bt crops, forcing farmers to use chemical insecticides as well as buying expensive Bt seed.
  • Bt toxins in GM Bt crops are not specific to insect pests, but harm beneficial insect pest predators and soil organisms.
  • Roundup used on GM herbicide-tolerant crops is not environmentally safe. It persists in the environment and has toxic effects on wildlife as well as humans (section 4).
  • Roundup increases plant diseases, notably Fusarium, a fungus that causes sudden death and wilt in soy plants and is toxic to humans and livestock.
  • The economic impacts on farmers of adopting GM crops were described in a study for the US Dept of Agriculture as “mixed or even negative”.
  • “Coexistence” between GM and non-GM crops is impossible as non-GM and organic crops become contaminated, resulting in lost markets and massive economic losses.
  • The possibility that GM traits could spread not only to related species by cross-pollination but also to unrelated species by horizontal gene transfer, should be investigated before commercialising GM crops.


“Over the past decade, corporate and government managers have spent millions trying to convince farmers and other citizens of the benefits of genetically modified (GM) crops. But this huge public relations effort has failed to obscure the TRUTH: GM crops do not deliver the promised benefits; they create numerous problems, costs, and risks; and … consumers and foreign customers alike do not want these crops.
“It would be too generous even to call GM crops a solution in search of a problem: These crops have failed to provide significant solutions, and their use is creating problems – agronomic, environmental, economic, social, and (potentially) human health problems.”

– National Farmers Union of Canada1

GM crops are promoted on the claimed basis that they give higher yields, reduce pesticide use, and benefit farmers and the environment. But independent studies either contradict these claims or show them to be inflated. GM crop technology is already failing under the onslaught of developments such as the spread of herbicide-resistant superweeds and pests resistant to the Bt toxin engineered into crops. These failures mean increasing costs to farmers and harm to the environment.

On-farm and environmental impacts of GM crops are not limited to the effects of the GM crop itself – for example, GM genes can spread to non-GM and organic crops. They also include the effects of the pesticide that the crop is engineered to contain or that it is designed to be grown with. Research shows that impacts are occurring from all these sources.

Some of these impacts occur with industrially-grown non-GM crops, too. But often, GM proponents obscure the negative effects of GM crops by comparing them with crops grown under chemically-based agricultural systems. They then draw the conclusion that GM crops have less harmful impacts.

But this is to compare one unsustainable agricultural system with another. A more meaningful comparison, and one that would help advance agricultural technology, would be to compare GM with agroecological or integrated pest management (IPM) systems. Many farmers outside the certified organic sector already use agroecological and IPM methods. This progressive trend should be encouraged. Instead, it is being delayed by the false hope offered farmers by GM crops. In contrast to agroecological methods, GM agriculture is an extension of chemically-based, high-input agriculture.

Below, we point out some of the flaws in the common arguments used to promote GM crops.

  • For references, please click here.
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