Posted by The online debate at The Economist Magazine continues. Dont forget to vote.
My rebuttal is here:
I agree with Charles Benbrook that “Bt crops have helped reduce insect feeding damage and lessened the need for toxic, broad-spectrum insecticides, and as a result, helped build populations of beneficial insects and promote above-ground biodiversity, two key sustainable farm-management goals.”
I also wholeheartedly agree with his statements that “Multiple-tactic systems composed of ‘many little hammers’ offer the best hope for sustained progress” and “Biotechnology can help create new hammers and harden existing ones”.
However, he incorrectly implies that GE crops are not being used as part of multiple-tactic systems today.
Bt crops are one of the few examples where a mandatory crop diversity strategy has been implemented. Global pest monitoring data suggest that this approach has helped to sustain the efficacy of Bt crops against most pests for more than a decade. For example, in Arizona, where an integrated pest management programme for Bt cotton is in effect, growers reduced insecticide use by 70% and saved more than $200 million.
Mr Benbrook describes an unlikely hypothetical scenario in which farmers can no longer rely on safe and cheap Bt insecticide sprays because Bt-resistant insects from cotton and corn “routinely overwinter in fruit and vegetable crops”. This has not occurred yet despite more than a decade of use of Bt crops on a cumulative total of more than 200m ha worldwide.
Moreover, while some pests of corn and cotton have evolved resistance to Bt toxins in GE crops, the first cases of insect resistance to Bt toxins occurred in response to spraying Bt insecticides on conventional vegetable crops–an approach favoured by organic farmers, who are not allowed to use transgenics. To help delay resistance, many newer varieties of Bt crops produce two or more Bt toxins with different modes of action.
The bottom line is that strategies for managing pest resistance are needed whether farmers use GE crops or conventional crops.
Contrary to Mr Benbrook’s assertion, Bt crops do promote self-reliance. Although farmers must buy the seed, this is the norm in any non-subsistence farming system where hybrid seed is used (organic and conventional). The advantage is that they do not need to buy and spray insecticides.
Mr Benbrook and I agree that overuse of a single herbicide can lead to the evolution of weeds that are resistant to that herbicide, which is problematic for farmers. Grower decisions to use repeated applications of particular herbicides have led to the evolution of resistant weeds. It is clear that herbicide tolerant (HT) crops need to be managed better for sustainability, rotating them with other crops or weed control methods. But this is also true of herbicide resistance traits developed through selective breeding or mutagenesis.
Mr Benbrook’s argument neglects an important aspect of HT crops that are resistant to the herbicide glyphosate (aka Roundup). Glyphosate (a class IV herbicide) has displaced much more toxic herbicides (classes I, II and III). In Argentina, HT soyabean farmers were able to reduce their use of toxicity class II and III herbicides by 83-100%. In North Carolina, the pesticide leaching was 25% lower in HT cotton fields compared with that of conventional cotton. Thus the main problem with weed resistance in HT fields is that it forces farmers to go back to the more harmful compounds that were in use before the widespread adoption of HT crops.
To mitigate the evolution of weed resistance, the newest HT varieties will have tolerance to more than one herbicide, which will allow easier herbicide rotation or mixing, and, in theory, help to improve the durability of herbicide effectiveness. Implementation of a mandatory crop diversity strategy would also greatly reduce weed resistance. These are also multi-tactic strategies.
Mr Benbrook’s account also does not consider other benefits of HT crops to sustainable agriculture. HT crops have been associated with an increased use of conservation tillage, in particular no-till methods, that can improve water quality and reduce soil erosion. That farmers who use GE crops are more likely to practice conservation tillage suggests the two technologies are complementary.
In Argentina and the United States, the use of HT soyabeans was associated with a 25-58% decrease in the number of tillage operations. Such reduced tillage practices correlate with a significant reduction in greenhouse gas emissions, which, in 2005, was equivalent to removing 4m cars from the roads.
Finally, by limiting the scope of his discussion to only two traits, Mr Benbrook overlooks the benefits of other GE crops on the market. For example, in the early 1990s, Hawaii’s papaya industry was facing disaster because of the deadly papaya ringspot virus (plants, like people, are susceptible to viral infection). The introduction of GE papaya resistant to the disease rescued the state’s papaya industry. Today, 80-90% of Hawaiian papaya is genetically engineered, and there is still no conventional or organic method to control the ringspot virus.
In many regions, the use of biotech seeds allows successful organic production, an important marketing niche, by reducing disease spread, while enabling the remaining 97% of agriculture to become more sustainable by reducing insecticide use. This is true for organic farmers growing cotton in Arizona and papaya in Hawaii as well as for other growers of non-GE seed. Cumulative benefits over 14 years are an estimated $3.2 billion for maize growers in Illinois, Minnesota, and Wisconsin, with more than $2.4 billion of this total accruing to non-Bt maize growers. Comparable estimates for Iowa and Nebraska are $3.6 billion in total, with $1.9 billion for non-Bt maize growers.
Mr Benbrook’s opening statement fails to address the dozens of other useful traits in the pipeline, including nitrogen use efficiency, provitamin A-enriched rice and drought tolerance.
Fourteen years of extensive field studies have demonstrated that genetically engineered crops are tools that, when integrated with optimal management practices, help make farms more sustainable. The vast benefits accrued to farmers, the environment and consumers explain the widespread popularity of the technology in many regions of the world.
November 11, 2010
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