I was just reading about chrysanthemum rust and how they dip the stools in hot water 115 deg F. Temp has to be precise, then into cool water. Might work on daylilies if they had small crowns. ???
Also I have put one I transplanted in the fridge for a few days and briefly in the freezer. I wrapped it in newspaper, then in plastic bag. It didn't develop rust but it turned out to be one that is pretty resistant anyway.
If I ever decide to get rid of a bad ruster I would first try those tricks, then try growing it inside as we don't have heating or air con. Would be good to find out if it worked. Can't see me doing it to all my plants but might for ones I was giving away.