You won't get rust on only one cultivar in the garden, it spreads on the wind and will affect others that are close enough - it sounds like what you have may be leaf streak. If you can't post a picture, these might help you compare
This first link has some pictures of leaf streak:
http://www.daylilies.org/ahs_d...
This one has pictures of rust and some other problems:
http://web.ncf.ca/ah748/FAQ.ht...
