Best bet is to get to know your producers--lots of "organic" growers don't get certified anymore, at least in Canada, because the "certification" seems to mean less over time and cost more/mean more hoops to jump through.
Our family likes as local and as organic as we can get it, knowing that the people we deal with don't grow any GMO crops. Our biggest concern is not about the fertilizers but the pesticides and herbicides used in regular agriculture, so we pick our battles. Everything is mixing and cross-pollinating out there over time so eventually there will be nothing we can do about it, but we do what we can to avoid it for now.