I suspect that planting herbicide resistant crops will lead to more chemicals being used on our fields, not fewer. But this isn't the whole story. Such sterile fields will offer little or no food or shelter to wildlife, and there is already evidence that the genes for herbicide resistance can spread to wild relatives of crop plants, leaving us with weeds resistant to weedkiller. And because the pesticide will be everywhere in the crop it is predicted that the pests will rapidly acquire resistance to it. Genetic material does not stay where it is put.
Pollen is spread by the wind and by insects.
GM crops can contaminate conventional and organic crops growing nearby. This cannot be right. Major problems may, as we are assured, be very unlikely, but if something does go badly wrong with GM crops we will be faced with a form of pollution that is self-perpetuating. I don't think anyone knows how to clean up after that sort of incident, or who would have to pay for it. I wonder about the claims that some GM crops are essential to feed the world's growing populations.