You're overthinking this a little. If Monsanto comes up with a new weedkiller, they have to prove that its safe for humans before its put into use. It has nothing to do with restaurants. Obviously stuff would be grandfathered in as well. But its a fantastic idea going forward.
If you require farmers to use "approved" processes for farming, but you don't require grocery stores and restaurants to use those farmers, then they will simply buy food from farmers that don't follow those principles.
If we're talking about domestic farmers, they're going to get caught at the same rate regardless of what you tell grocery stores and restaurants to do.
If you mean international farmers, I think it's obvious you'd have to apply the same rules to imported food, so no they won't simply buy food that doesn't follow the rules.
But also, even if we did require grocery stores and restaurants to use certified farmers in some way, that wouldn't be hard at all! That's not even in the same ballpark as requiring scientific proof of chemical safety.
They probably haven't thought through all the good chemicals have done. If we stopped all progress in chemicals 100 years ago our world would like a very different place.
A less wealthy place where more people died of starvation.
Great, so we're just going to need a few long term clinical trials assessing the impacts of each of ingestion, skin contact, inhalation, eye exposure, etc. separately for childhood exposure, adult exposure, exposure during pregnancy, acute exposure, chronic exposure, and so on. 100 billion dollars and thirty years later, maybe you can start provisionally selling your slightly better scotch tape.
That’s a little disingenuous. Something like an herbicide that’s broadly applied to fruits and vegetables that millions of people are eating should be under far higher scrutiny than a niche product that has limited human contact.
Things that don't have much human contact in the general population can have significant human contact during the manufacturing process of products containing or processed with them.