What if the farmer was trying to clear the land with roundup and the accidental gmo modified crops prevented him from doing so. Could he sue for damages?

Perhaps! Though in this case it seems he engaged in the behavior over an extended period of time and did not consider the patented crops a problem.

No, if he didn't save seeds from crop plants on that land. That saving of seeds after spraying was the incriminating act.

How does the doctrine of first sale not apply here?

I could make up some convoluted argument but… the neighbor conducted the first sale so this should have extinguished any further patent claim. Of course, IANAL.

He is not reselling individual seeds. He is manufacturing new seeds. He is not allowed to do that, and particularly not allowed to do that with intent.

From wikipedia:

>A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention.

In this, letting the plant reproduce arguably falls under "making" (ie. manufacture) of the patented thing (the genetically modified plant).