The fed guidlines for a hazmat are a "reportable quantity". For something like Weevilcide, that is more than .01 grams. For Roundup and most restricted use pesticides, more than 119 gal. For NH3, any amount. Your best best is to have the cdl and endorsements. Getting pulled over is the least of your concerns. Have a wreck with a spill, and the ticketbook comes out. Make sure you have the chemtrec number and are signed up (its free until you call them). Also, your reportable quanntity is cumulative. So if you have Roundup tank mixed with atrazine, they each count separately.

Also, by not having the endorsements if there is injury or damage, you have just set yourself up as a reckless scofflaw, not a trained professional who had an unfortunate incident.

Also, many states do not allow you to transport mixed loads. "Hotloading" is prohibited and all mixing must be done "in field". Also, your liability insurer may not cover you if you are hot loaded. Jugs and shuttles are DOT approved carriers, but your spray tank may not be certified to haul hazmat.