This strategy was supported by claims from Monsanto that glyphosate resistance was unlikely to develop naturally in weeds when the herbicide was used properly. As late as 2004, the company was publicizing a multi-year study suggesting that rotating crops and chemicals does not help to avert resistance. When applied at Monsanto’s recommended doses, glyphosate killed weeds effectively, and “we know that dead weeds will not become resistant”, said Rick Cole, now Monsanto’s technical lead of weed management, in a trade-journal advertisement at the time. The study, published in 2007, was criticized by scientists for using plots so small that the chances of resistance developing were very low, no matter what the practice.
Glyphosate-resistant weeds have now been found in 18 countries worldwide, with significant impacts in Brazil, Australia, Argentina and Paraguay, says Ian Heap, director of the International Survey of Herbicide Resistant Weeds, based in Corvallis, Oregon. And Monsanto has changed its stance on glyphosate use, now recommending that farmers use a mix of chemical products and ploughing. But the company stops short of acknowledging a role in creating the problem. “Over-confidence in the system combined with economic drivers led to reduced diversity in herbicide use,” Cole tells Nature.
On balance, herbicide-resistant GM crops are less damaging to the environment than conventional crops grown at industrial scale. A study by PG Economics, a consulting firm in Dorchester, UK, found that the introduction of herbicide-tolerant cotton saved 15.5 million kilograms of herbicide between 1996 and 2011, a 6.1% reduction from what would have been used on conventional cotton. And GM crop technology delivered an 8.9% improvement to the environmental impact quotient — a measure that considers factors such as pesticide toxicity to wildlife — says Graham Brookes, co-director of PG Economics and a co-author of the industry-funded study, which many scientists consider to be among the field’s most extensive and authoritative assessments of environmental impacts.
The question is how much longer those benefits will last. So far, farmers have dealt with the proliferation of resistant weeds by using more glyphosate, supplementing it with other herbicides and ploughing. A study by David Mortensen, a plant ecologist at Pennsylvania State University in University Park, predicts that total herbicide use in the United States will rise from around 1.5 kilograms per hectare in 2013 to more than 3.5 kilograms per hectare in 2025 as a direct result of GM crop use.
To offer farmers new weed-control strategies, Monsanto and other biotechnology companies, such as Dow AgroSciences, based in Indianapolis, Indiana, are developing new herbicide-resistant crops that work with different chemicals, which they expect to commercialize within a few years.
Mortensen says that the new technologies will lose their effectiveness as well. But abandoning chemical herbicides completely is not a viable solution, says Jonathan Gressel, a weed scientist at the Weizmann Institute of Science in Rehovot, Israel. Using chemicals to control weeds is still more efficient than ploughing and tilling the soil, and is less environmentally damaging. “When farmers start to use more sustainable farming practices together with mixtures of herbicides they will have fewer problems,” he says.
GM cotton has driven farmers to suicide: False
During an interview in March, Vandana Shiva, an environmental and feminist activist from India, repeated an alarming statistic: “270,000 Indian farmers have committed suicide since Monsanto entered the Indian seed market,” she said. “It’s a genocide.”