Corn reproduction can be unruly, as I wrote here. It's hard to segregate different crop types. But if you are willing to accept a few illegitimate kernels, it is possible to maintain relatively isolated strains. It all depends on your tolerance for mixing: It's pretty easy to prevent 95 percent of crosses -- it's that last 5 percent that's tricky, and the last .01 percent is nearly impossible.
One of the people I’d wanted to talk to about the issue of intermingling genes was Nicholas Kalaitzandonakes of the University of Missouri. As an economist, Kalaitzandonakes is strictly concerned with the economic effect that errant pollen can have on a farmer. And what Kalaitzandonakes has seen in his experiments has made him optimistic for a future where many different types of corn -- genetically modified or no -- grow side by side without much mixing.
Most pollen falls near the stalk, and planting a barrier row of corn can help protect a field, he said. Furthermore, you can use time to isolate corn as well as space. The flowering times of the plants are fixed, so if you plant one corn a few weeks after another, they won’t crossbreed, even if they are side by side.
Of course, none of this matters if you want perfect purity: Sooner or later a grain of pollen will travel far enough to find a receptive tassel. But hardly anyone is asking for perfect purity. From those concerned that genetically modified seeds might have some unknown health risk, to those who want to make sure that their sweet corn doesn’t have blue kernels, most people allow a margin of tolerance.