I'm getting a bit lost keeping up with the changes, but the only major disease of daylilies that is an obligate parasite is daylily rust. Nitrogen and potassium are not the only nutrients that have an influence on plant diseases, there are whole books devoted to the topic of nutrients and plant diseases. I have one, Mineral Nutrition and Plant Disease, Datnoff et al, APS Press. 278 pages devoted solely to the various nutrients and their influence on increasing or decreasing specific diseases.
Re nutrients and spring sickness, I had my daylily leaves tissue tested and the only nutrient that was too low was manganese (which seems not to be an uncommon nutrient deficiency in daylilies, often related to the pH).
I am familiar with the Botrytis/spring sickness article. I find it somewhat difficult to see a disorder of daylilies that has been known since the early 1940's (at least) as an emerging plant disease! Note that they did not reproduce spring sickness experimentally with the new Botrytis whereas the researcher who looked at Aureobasidium microstictum's potential involvement did reproduce something he felt looked like spring sickness when injecting that latter fungus into healthy daylilies. (Yes, A. microstictum is also the fungus that causes leaf streak). See these references from my spring sickness task force web site (the two lower ones are for bulb mites):
Kobayashi, H. 1998. Aureobasidium microstictum (Bubak) Cooke, The causal agent of leaf streak of daylily (Hemerocallis L.) and its involvement in spring sickness of daylily, M.Sc. thesis, Ohio State University.
Labanowski, G.S., Soika, G. 1992. Occurrence and Injurious Effects of Rhizoglyphus echinopus - A new pest of Hemerocallis hybrida. Acta Horticulturae, 325;739-741.
Muller, P.J., Hollinger, T.C. 1980. Damage by Rhizoglyphus mites in some ornamental bulbous crops. Acta Horticulturae, 109;449-456.
Yes, there are plant pathogenic nematodes that attack daylilies.
Re hydrogen peroxide for rust, this has been studied. There's a citation on my daylily rust info site in the literature list pages but you can get there direct from here:
http://www.sciencedirect.com/s... (Hydrogen peroxide and dioxide are the same thing as Tina notes above).
