That's a very interesting concept. i like this question. idk anything about this news but, there's plenty of factors that would take part in my personal decision, i don't think i could make a decision one way or the other with what's there.
for me, if i were the farmer, it'd depend on questions such as:
"exactly how much of the land did this occupy?"
"Who was aware and when?"
"did the seeds kill what had already been sown, or is the land fallow?"
"could it be taken to a higher court?"
"did the farmer invest anything for that crop to yield?"
Basically, i wouldn't argue their patent rights on the plant, afterall, it really is intellectual property manifested into a physical investment. I mean, genetics and breeding too is work afterall.
But if i were the farmer...I would argue my liability, and try to settle outside of court...but if not, take to the court the chance to sell my monsanto yield back to them at the very least or even counter-sue depending on the full answers of above questions.