Becky, perhaps either your rust hasn't read the study or there is some other factor at play between your shade and sun beds. For example is the shade provided by trees in which case the night temperature would normally be lower over the open beds, is there a difference in air circulation, different genetic lines in the different beds, differences in the prevailing wind direction?
Tina, I think if rust could be killed by high temperatures we wouldn't still have it in Florida and Texas for example. I understand it just takes a break during the hottest periods. In the U of Guelph study described in part on my web site (on the spore longevity page, and available in full PDF from there) daylilies were inoculated with rust but no pustules appeared for seven weeks or more during hot weather.
Theoretically if heat killed all the foliage on all the daylilies in an area then presumably it would have the same effect as when winter kills the foliage since the rust cannot survive without living tissue (except as spores which can only infect living tissue) but I don't think it's likely that all daylilies in an infected garden would have total foliage kill during hot weather as happens with cold in the colder climates.
