Several posts here have looked at whether taxing bud at one rate and trim at another is viable.
One argument that the line is self-enforcing, as bud is smoked and trim made into concentrates. But even without a tax incentive to put bud in the trim pile, businesses do just that. Here is an ad, downloaded 14 September 2014, promising concentrates made from . . . ALL BUD NO TRIM!
The Center for New Revenue 