Most of the benefits for farmers and the environment claimed for GM crops are either exaggerated or false. For example, contrary to frequent claims, GM crops have not increased intrinsic yield. Crop yields have increased over the past decades, but this is due to successes in conventional breeding, not GM traits.
Neither have GM crops decreased pesticide use. The adoption of GM Bt maize and cotton has resulted in a slight decrease in the volume of insecticide sprays, but this decrease is likely to be unsustainable as pests gain resistance to the Bt toxins and secondary pests take over. Also, the reduction in insecticidal sprays is dwarfed by the massive increase in herbicide use caused by the adoption of GM herbicide-tolerant crops. The adoption of these GM crops has caused farmers to spray 383 million more pounds (174 million kg) of herbicides than they would have done in the absence of GM herbicide-tolerant seeds.
This increase is largely due to the spread of weeds resistant to glyphosate, the herbicide most commonly used on GM crops. As a “solution” to the problem of glyphosate-resistant weeds, biotech companies have developed crops engineered to tolerate several different herbicides, including potentially even more toxic herbicides such as dicamba and 2,4-D (an extremely toxic ingredient of Agent Orange). The resulting chemical treadmill only benefits the GM seed companies, which profit from each failure of their technologies because the failure creates a new opportunity for them to sell more chemicals in increasingly complex mixtures. Claims for the environmental friendliness of the no-till farming system as practised with GM herbicide-tolerant crops are also unjustified.
Glyphosate over-use is also causing other problems for farmers, such as reducing crop vigour by making soil nutrients unavailable to crops and causing or exacerbating plant diseases that impact yield. Manufacturer claims that glyphosate/Roundup is an environmentally benign herbicide with low toxicity have proved to be false, with a growing number of studies showing that it persists in the environment and has toxic effects, in addition to studies showing that it is toxic to humans and causes birth defects and cancer.
Claims of reductions in insecticide use through Bt crops are suspect when it is considered that the entire GM plant is an insecticide. Also, Bt crop technology is being undermined by the emergence of resistant and secondary pests, which force farmers to go back to spraying complex and expensive chemical cocktails. And the increased use of insecticidal seed treatments on GM and non-GM seed alike raises the possibility that insecticide use has not been reduced through Bt crops but that it is simply less visible to farmers and consumers.
Statements that the Bt toxin in Bt crops only affects insect pests have been shown to be false by studies showing negative effects on a wide range of organisms, including beneficial insects that help protect crops and beneficial soil organisms that enhance crop growth and health.
Economic impacts of GM crops on farmers appear to be variable. Reports have emerged of escalating prices for GM seeds and the chemicals they are engineered to depend on. This pattern is enabled by the consolidation of the seed market under the control of the GM and agrochemical industry and the absence of real competition.
At odds with claims that GM crops increase farmer choice, in reality their introduction marks the disappearance of farmer choice due to two mechanisms. First, as the GM industry gains control over the seed market in a region, desirable non-GM seed varieties are pulled from the market. Second, the biotech industry lobbies for “freedom of choice” for farmers, claiming that GM and non-GM crops (including organic) can “co-exist”. This opens the door for GM crops, causing farmers who wish to grow non-GM or organic crops to lose their freedom of choice due to GM contamination. Time and again, this has resulted in lost markets and increased costs to farmers and the food and feed industry.
GM traits can spread to other crops, wild plants, and other unrelated species by horizontal gene transfer (HGT) through several mechanisms, some of which are more likely than others. The potential consequences of HGT have not been adequately considered by regulators.