"For example, there is ample evidence that insects can develop resistance to BT, if it is used as the sole method of pest control. Effective methods for slowing the spread of insect resistance include crop rotation, intercropping and planting refuges of non-BT cotton and non-crop species"
The use of Round-up ready crops means that farmers are using Round-up. What happens when weeds become resistant to Round-up? What happens to an ecosystem that is dealing with the run-off from Round-up treated fields? I've read articles based on good science that would indicate that in the long run, methods that rely on building good soil out-produce methods that depend on technology. for example- fields that were planted using GMO crops using conventional methods lose soil each year. Fields planted using sustainable methods gain soil. Over a ten year time span, both fields will have approximately the same yield. however, the fields planted using sustainable methods will produce crops even during years when drought conditions occur. Studying GMO crops in isolation misses the larger picture.
http://www.ag.iastate.edu/farms/02reports/ne/OrganicConvSystems.pdf
http://phys.org/news/2012-04-debate-conventional-agriculture-combining-approaches.html
http://grist.org/organic-food/crop-yields-are-only-part-of-the-organic-vs-conventional-farming-debate/
http://www.agroecology.org/Case%20Studies/strawberries.html
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