While the yield benefits of currently commercialized GM crops in developed countries such as the U.S. may not be large, surveys of farmers in both developed and developing countries show that GM crop farmers in developing countries have achieved much greater yield increases. Currently commercialized technologies are intended to improve pest management and therefore reduce or eliminate losses for insect damage or weed competition. In developed countries, these technologies have substituted for other pest-management practices and have been adopted for reasons other than yield improvement, such as reduced costs and management time. In developing countries, these same technologies can improve yields substantially if farmers lack access to effective conventional pest-management tools, such as pesticides.
With respect to the referenced paper, I believe the authors' “conclusions” are better characterized as assertions. Regarding the impacts of GM crops on both yields and pesticide use, the study makes gross comparisons between yields and pesticide use in North America and Western Europe, drawing “conclusions” about the impact of GM crops, whereas of course there are many other factors that influence yields and pesticide use, such as climate, soils, topography, farming system and government subsidies.
For corn, yields in the U.S. and Western Europe are comparable. The impact of currently commercialized insect-resistant and herbicide-tolerant crops in the U.S. has been to reduce the reliance on conventional insecticides, to allow growers to use more environmentally friendly herbicides and to reduce costs, and in some years increase yields, though not dramatically. European growers are able to achieve high yields using conventional pest-management practices, such as pesticides and tillage. For example, European maize growers use herbicides on approximately 90 percent of maize acreage, use tillage on over 70 percent, and continue to use broad-spectrum insecticides to control the most troublesome insect pests [M. Meissle et al., 2010, “Pests, pesticides use and alternative options in European maize production: current status and future prospects,” Journal of Applied Entomology, vol. 134, pp. 357-375].
For rapeseed, yields in Canada have historically been much lower than in Western Europe. There are many differences between the production systems of Canada and Western Europe. Rapeseed production in Western Europe is best characterized as an intensive, high-input, high-yield system, encouraged by a favorable climate and government subsidies, while Canadian production uses fewer inputs and is lower yielding. Further, European growers plant mostly oilseed rape, which is genetically distinct from inherently lower-yielding canola that is grown in Canada. Similarly for wheat, yields in the U.S. have historically been much lower than in Western Europe, due to the more intensive, high-input system used by wheat farmers in Europe.
Regarding pesticide use, the authors’ conclusions are based on comparing trends in overall pesticide use, for all crops combined, in the U.S. and various Western European countries. The data are from FAO, which reports annual estimates of pesticide use in metric tons per 1000 hectares by country. Because the FAO data present only an aggregated estimate of pesticide use for all crops produced in a country, it would be extremely difficult to draw any conclusions based on these data alone. Further, despite the assertion by the authors that pesticide use reductions were observed in Switzerland and Germany (with no data shown in the paper), current FAO data show overall pesticide use increasing in both countries between 1995 and 2010. Perhaps most importantly, though, comparing trends in the aggregate amount of pesticides used is problematic, as pesticides are applied at vastly different rates and are inherently different in their potential environmental and human health impacts.
In the future, it is likely that developing countries will continue to have the most to gain from GM crops that are currently under development, such as nitrogen use efficiency, drought and salt tolerance and nutritional quality. Each of these technologies offers solutions to production or nutritional constraints that are more acute in developing countries than in the U.S. and Western Europe.