The best I understand is that daylily rust spores change from summer to winter spores with the drop in temperature. Then once they change into winter spores they can't change back into summer spores with out a host plant being available (Don't remember the name off hand). So I can see they can keep the spores alive, and you are right it does not actually kill them (from what I have been able to understand) it just changes them. I am sure others can give a much better explanation.