I have read that rust will not kill a daylily, but I have had a couple that I blamed rust for killing them. I have no scientific evidence of it, but it seemed to weaken the plants to such a point they died. It could have been the actual cause was something else. But if rust weakens a plant so it loses it's ability to survive other stresses, then to me in essence the plant was killed by rust. Even though that might not be the "official" cause of death.
