Arlene - I do a search as Larry instructed above and often just put in rust resistance and not necessarily a rating. But I do it both ways to find all the cultivars. When I do that, the list it typically not very long because I am also searching for ev or sev at the same time. Larry is right ... which thousands of registered cultivars, only a small percentage has been rated for rust.
I also look at pedigree. ATP has an awesome database because not only can you do a search by name, but the daylily database will list parents of a cultivar (if known). You can click on each of the parent's names and check their rust resistance. And often I go on to the grandparents to also check them. If I see any rated as rust susceptible of 4.0 or 5.0 .... I don't bother considering the cultivar. The genes are there for rust susceptibility, IMHO. Granted, I do know that some children from such plants can show rust resistance, but since I like to hybridize, I prefer not to take the chance. There are too many other daylily cultivars out there for me to try, so I don't waste my time or money on a possible rusty plant or a plant with genetics that might show rust susceptibility.
I hope this info is helpful.
I also like some of the older cultivars. Breeding them with newer ones might surprise you with some very nice, rust resistant children!
