The practices that Sue (Sooby), Michele, and Glen outline track with information in the linked article, since even the chemicals used to suppress rust do not kill it, and an infection that is not yet visible at the time of digging and packing can take, based on what I read of the article, two weeks to two months before it erupts (longer than fans could be kept and watched before shipping). What was new is Sue's information about fertilizers and rust, expanded upon below in a follow-up post by her. They are very helpful details to learn.
Regarding resistance, there hasn't been any research I've heard of that indicates daylilies might be able to independently develop resistance to rust on their own. Scientists continue to recommend that cultivars chosen for hybridization include rust resistant parentage as the means for passing resistance on to offspring. Studies done in the first fifteen years following the discovery of daylily rust found that of over 800 tested cultivars observed in university experiments, over half were observed to be resistant.
So, there is a wide range of impact and response to rust infections - and those hybridizers who do not suppress rust have a built-in chance to observe seedlings' performance with rust in their own nurseries. Those who do spray may also rely on external test gardens that have rust to ship out seedlings and get informal reports back about their performance. Following the consistent advice of rust researchers, hybridizers who include rust resistant cultivars in breeding choices will be selecting for increased chance of resistance in offspring.
Spores can be mechanically transferred, but the study linked above also observed that spores appeared to be less likely or able to spread between plants that were between 7-33 feet or more away from a source of infected foliage. High temperatures (104 F) in a greenhouse also seemed to suppress rust development, but did not stop it from progressing once the cultivars were moved outside to lower temperatures.
Oh, and in regard to Glen's #5 suggestion, I'd like to go on the list of disliked relatives (as if I'm not already lol) to get rusty fans sent rather than just discarded! California only prohibits potted plants from coming in due to soil-borne pathogens, but has no restriction on rusty daylilies as long as they are shipped as bare-root plants. Since I am a home hybridizer, it would be most helpful to me to have a rust source to maintain within at least 30 feet of any seedlings.
