It's not that they have no control over it. It's that unforeseen consequences (herbicide resistant weeds) have ended up making things worse rather than better. So now there's a sort of herbicide arms race. For example, seed companies are getting approval to stack their GMO seeds with multiple herbicide resistance, and they're advising farmers to buy more varieties of herbicide to deal with resistant weeds. It's great for them-- they get to move more product.
Not so great for farmers. The amount of Roundup required to control weeds has steadily risen over the last few years, so that application rates are much heavier now than they were when Roundup ready crops were first introduced. It would be naive to expect that the same thing won't happen again with the additional and less benign herbicides that will be required to control roundup resistant weeds.
2,4-D is poised to step up, since Dow AgroSciences is developing resistance to this herbicide in their new GMO varieties.
Maybe it's just me, but this seems like the sort of treadmill that just keeps going faster until you go flying off, no matter how fast you run.