See this Institute for Agriculture and Trade Policy article about whether it is possible/practical to actually produce/deliver a GMO-free product to market. There are several sticking points to pulling this off all along the process, from sowing & pollination, harvesting, storing, and transporting grain. The concept of Identity Preservation has been around for some time. If the procedures developed for IP grain are specified in a grain contract and followed to the letter, it is possible to bring to market a GMO-free crop. However, this chain of evidence is only as strong as each link. There is extra labor involved at each step, for instance making sure that equipment is cleaned between crop runs (extra labor), or that grains are stored in separate containers in storage (extra investment for elevator operators). There are financial incentives to pull this off, since contracts for non-GMO crops pay extra. Organic growers have been successfully pulling it off for some time. The stakes are even higher now with the proliferation of GM crops. This will be a topic that we’ll be watching more carefully in the future. Testing is also going to be more critical to make sure that crops are not tainted with GMOs.