They will be government controlled cash crops. It will be a controlled and regulated(mega)tax cash cow, like tobacco and alcohol is. Bootlegging and illegal cultivation will still give you serious prison time.
Is that the case with alcohol today? Is it a serious crime to make your own gin?
Exactly, and there is no reason that the black market would be any larger with legal marijuana than it currently is with alcohol.
That means the cartels would take a big hit since most of their revenue comes from mj - 62% according to the ONDCP.