Can't you build a patented device personally without a license?
The crux here seems that seeds for sowing are protected by the patent, but NOT protected for consumption. If this farmer purchased seed from a third party, and then used these seeds only for internal sowing use, only selling his seed for consumption - is that an actual violation? I (perhaps mistakenly) understood that you were allowed to build anything for your own use without patent licensing fees, but you could not sell those same items for commercial gain. If he's not selling GM seeds for sowing, and only for consumption (and sells them under that condition), he's not violating the patent.
Example: I make, in my backyard, a patented Soybean Harvester out of plans I obtained from the USPTO, or by taking pictures and measurements of my neighbor's. I then use that to harvest my soybeans. It works so well I make three more for my farm. When they break down, I re-build them. Am I liable for patent infringement? I'm not selling the patented Harvester - only using it myself.
I'm sure there are not-lawyers here who can sort this out.