You are required to have an EPA registration to manufacture and sell in the United States. You are required to register your product (this are NOT supplemental) in a state prior to transferring, storing, marketing, using, or offering. So you must have at a minimum the Federal Registration and a single state registration (i.e. the State you are in). Many pesticides have such low volume in a region or cannot comply with a particular state statute or regulation, that the manufacturer will only have some registrations. For example if I think I will only sell $3,000.00 worth of pesticide into a State that Charges me $2,000.00 per year per registration then it makes sense to not register in that State. Another example would be California passes a law banning a specific chemical, such as they did with creosote many years ago, I simply stopped registering my creosote based pesticide in California.
However, the offering or advertising of the pesticide not registered in that state is now illegal. So I must either ensure that any such efforts are never seen by residents of that State while they are in that State. And I will be legally responsible if someone purchases my product outside the State and brings it into the State and uses it (of course they will be fined too, which isn’t comforting). So most manufacturers will print in red, bold font, one or two points larger than the rest of the label or advertising text, “This product not available in CA, MI, CO, NY, & MA.” in a very prominent place.
Specific to selling on Amazon, any listing must be legal to posses, use, and sell in ALL 50 States. So without a The Federal EPA Registration and Registrations in all 50 States, you can’t list your product on Amazon. Remember that you can be fined, and possibly imprisoned, for selling an unregistered pesticide. Years ago, the EPA didn’t spend much time on enforcement, instead individual States would do the enforcement, and the EPA would act like a clearing house and provide authoritative guidance. Back then one State would begin enforcement and seek assistance from the EPA, the EPA would inform all other States of the enforcement along with all information obtained. Back then the EPA would only ‘Make a Federal case out of it’, if it was especially egregious, after the other States had already gone to court and gotten convictions or settled, the exception was illegal imports. Today, the EPA is more likely to take the lead in enforcement and investigation, with the States tacking on after.
It doesn’t really matter if the EPA or a State starts an investigation or takes enforcement action, you should be aware that if you get caught in one state every other state and the EPA will know about it and will also begin their own investigation and/or enforcement.