OK, I wrote out my reply before pasting it in so I wouldn't lose it again.
Rust is a constant problem here. I do not spray any fungicides, though. That is a decision I made, so I have to put up with the consequences. Here is how I try to minimize rust problems to keep it manageable.
1. I eliminate "rust bucket" cultivars—those that have had several bad outbreaks in the same season or several seasons in a row. With so many available, it's not worth keeping them.
2. For those cultivars that have gotten a little rust now and then, I trim the rusty leaves immediately and spray the plant with Green Magic, a product I read about. It's actually an organic cleaning product. I cannot cite any study that indicates it works, but my impression is that it helps retard the development of new spores.
3. I put new cultivars that have developed some significant rust "on probation"—I dig them up, pot them, cut them back, spray them with Green Magic, and isolate them. If they get rust again, out they go.
4. I do a lot of homework on cultivars to add to my garden. The rust resistance scores in the database are a starting point. In my experience, a score of 1.0 is a good indicator but is not by any means proof that a daylily won't develop rust here. (Similarly, sometimes a daylily that is supposedly very susceptible will do fine here, presumably because it is immune to the rust strains I have.) If there is nothing about rust in the database, I will try to research the parentage. If I can't find out anything that way, sometimes I can get info about rust resistance from others in my zone who have grown the plant successfully.
Miscellaneous observations:
• In several cases, daylilies that got some rust one season, but which I spared, have been fine the next. I don't know whether this is because the plant developed some resistance or because conditions changed.
• Some of my daylilies show a little rust but then seem to shrug it off.
• Other cultivars show rust only in the fall when they are beginning to die back. I can live with this because I am removing spent foliage anyway.
• I keep careful records of cultivars that have been rust-free here. These are the only ones I will share with local friends.
• I have made several purchases from Ron Reimer and Brian Reeder, who have both made rust resistance a priority in their programs. I have three Reimer daylilies and nine of Reeder's, all labeled highly resistant. All have been as advertised and have shown no rust.
