your sounding like you have power as a grower! (admirable!)
All it will take is for one mill to stop taking grain for bread and then it will be the same everywhere.
If I had some power, I'd be saying that if we did ban it pre-harvest, that imported grain should be tested for residues at the dock prior to going to a mill.
Its not tricky. If folk dont want to eat is, safe or not, then imported grain should meet the same requirements.