I was sent a short article from Science this week that discussed the impact of biotech crops on organic farms. The article is entitled "Can Biotech and Organic Farmers Get Along?" discusses issues with the science and politics surrounding GMO crops and gene flow to organic crops.
Science (online at www.sciencemag.org) is not open access so I can't post the pdf here. However, non-subscribers can read a summary and listen to a podcast interveiw with the author, Erik Stokstad, at this link (if you are at an institution that subscribes to Science, you can get the full article too). I think the podcast interview is interesting and a good presentation of the issue.
http://www.sciencemag.org/content/332/6026/166.summary?sid=ff187a4f-2cf2-4e51-bc6f-b3728d79fc59
The article and interview discussed quite a bit about the potential for cross pollination (pollen-mediated gene flow) and seed movement (seed-mediated gene flow). One thing that the article highlighted for me was the regulatory hurdles (and sometimes contradictions) faced by farmers of all stripes. In the US, certified organic production requires following a prescribed set of production practices. In this situation, if a farmer followed organic production practices in a field but an incidental amount of gene flow from a neighboring biotech crop field occurred, that crop could still be legally labeled as organic. However, if that same farmer wanted to export that crop to a zero-GMO tolerance country, the crop would not meet standards.
I agree with one of the plant geneticists quoted in the article (Pat Byrne from Colorado State University) who said "As long a zero tolerance is insisted upon, you can forget about coexistence". However, if a threshold level can be defined and agreed upon, coexistence is very possble. I also appreciated the final quote in the article (from Molly Jahn at UW Madison) "It's possible for reasonable people to commit to a way forward, grounded in science, with reasonable standards".
In California, this issue is greatest with the on-again, off-again deregulation of Roundup Ready alfalfa. For more info on RR alfalfa, see this UC publication - Roundup Ready Alfalfa, an Emerging Technology. Several important cropping systems around the country are affected and problems are likely to increase as new crop technologies are developed and undergo regulatory review.