I guess it depends on what you consider a "cold" winter. The general rule of thumb is that daylily rust may survive the winter in Zone 7 or it may not, depending on the location and the conditions that winter. Warmer than that, i.e. Zone 8 and warmer, it likely will survive. In zone 6 and colder zone it won't normally survive. It definitely doesn't survive here in Zone 4 because I've twice introduced it to experiment with. In other experiments it did not survive in Ohio, nor did it persist without Patrinia in a relatively mild winter in Japan where the daylilies were deciduous.
If your daylilies all die back to the ground for the winter then it cannot survive without the presence of the alternate host, Patrinia spp. because rust diseases need a living host. The "winter spores", the black teliospores, that form towards the end of the season can survive on dead daylily tissue but cannot re-infect daylilies in the absence of Patrinia to re-start the process. In zone 5 you shouldn't have rust overwinter.
I don't see that spraying the soil when preparing for new arrivals would be worthwhile. It would be the new arrivals that bring in the rust.
