Genetic engineering has failed to increase the yield of any food crop but has vastly increased the use of chemicals and the growth of "superweeds", according to a report by 20 Indian, south-east Asian, African and Latin American food and conservation groups representing millions of people.
The so-called miracle crops, which were first sold in the US about 20 years ago and which are now grown in 29 countries on about 1.5bn hectares (3.7bn acres) of land, have been billed as potential solutions to food crises, climate change and soil erosion, but the assessment finds that they have not lived up to their promises.
The report claims that hunger has reached "epic proportions" since the technology was developed. Besides this, only two GM "traits" have been developed on any significant scale, despite investments of tens of billions of dollars, and benefits such as drought resistance and salt tolerance have yet to materialise on any scale.
Most worrisome, say the authors of the Global Citizens' Report on the State of GMOs, is the greatly increased use of synthetic chemicals, used to control pests despite biotech companies' justification that GM-engineered crops would reduce insecticide use.
In China, where insect-resistant Bt cotton is widely planted, populations of pests that previously posed only minor problems have increased 12-fold since 1997. A 2008 study in the International Journal of Biotechnology found that any benefits of planting Bt cotton have been eroded by the increasing use of pesticides needed to combat them.
Additionally, soya growers in Argentina and Brazil have been found to use twice as much herbicide on their GM as they do on conventional crops, and a survey by Navdanya International, in India, showed that pesticide use increased 13-fold since Bt cotton was introduced.
The report, which draws on empirical research and companies' own statements, also says weeds are now developing resistance to the GM firms' herbicides and pesticides that are designed to be used with their crops, and that this has led to growing infestations of "superweeds", especially in the US.
Ten common weeds have now developed resistance in at least 22 US states, with about 6m hectares (15m acres) of soya, cotton and corn now affected.
Consequently, farmers are being forced to use more herbicides to combat the resistant weeds, says the report. GM companies are paying farmers to use other, stronger, chemicals, they say. "The genetic engineering miracle is quite clearly faltering in farmers' fields," add the authors.
The companies have succeeded in marketing their crops to more than 15 million farmers, largely by heavy lobbying of governments, buying up local seed companies, and withdrawing conventional seeds from the market, the report claims. Monsanto, Dupont and Syngenta, the world's three largest GM companies, now control nearly 70% of global seed sales. This allows them to "own" and sell GM seeds through patents and intellectual property rights and to charge farmers extra, claims the report.
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The study accuses Monsanto of gaining control of over 95% of the Indian cotton seed market and of massively pushing up prices. High levels of indebtedness among farmers is thought to be behind many of the 250,000 deaths by suicide of Indian farmers over the past 15 years.
The report, which is backed by Friends of the Earth International, the Center for Food Safety in the US, Confédération Paysanne, and the Gaia foundation among others, also questions the safety of GM crops, citing studies and reports which indicate that people and animals have experienced apparent allergic reactions.
But it suggests scientists are loath to question the safety aspects for fear of being attacked by establishment bodies, which often receive large grants from the companies who control the technology.
Monsanto disputes the report's findings: "In our view the safety and benefits of GM are well established. Hundreds of millions of meals containing food from GM crops have been consumed and there has not been a single substantiated instance of illness or harm associated with GM crops."
It added: "Last year the National Research Council, of the US National Academy of Sciences, issued a report, The Impact of Genetically Engineered Crops on Farm Sustainability in the United States, which concludes that US farmers growing biotech crops 'are realising substantial economic and environmental benefits – such as lower production costs, fewer pest problems, reduced use of pesticides, and better yields – compared with conventional crops'."
David King, the former UK chief scientist who is now director of the Smith School of Enterprise and the Environment at Oxford University, has blamed food shortages in Africa partly on anti-GM campaigns in rich countries.
But, the report's authors claim, GM crops are adding to food insecurity because most are now being grown for biofuels, which take away land from local food production.
Vandana Shiva, director of the Indian organisation Navdanya International, which co-ordinated the report, said: "The GM model of farming undermines farmers trying to farm ecologically. Co-existence between GM and conventional crops is not possible because genetic pollution and contamination of conventional crops is impossible to control.
"Choice is being undermined as food systems are increasingly controlled by giant corporations and as chemical and genetic pollution spread. GM companies have put a noose round the neck of farmers. They are destroying alternatives in the pursuit of profit."