My herbicide supply store tells me that Plateau is reputed to work o.k. but that it is quite expensive, and they don't have any local users of it to assess it's affectiveness first hand. I have never tried it, nor do I know anyone that has. The supply store guy with whom I spoke also said that he didn't really think there was a clear cut "winner" to use on johnson grass in bermuda, i.e. one that kills out johnson grass and leaves bermuda undamaged. If your johnson grass infestation is still pretty manageable you may want to just go and do spot spraying with Roundup or anything else that will kill it, using a backpack sprayer or a small Spiedel weed wiper. And of course try to kill it before it goes to seed. That should cause only minimal damage to the bermuda, albeit a somewhat labor intensive method.