The problem may be voles or moles. If the root mass is diminished, the foliage will die back. If you have plants, as you say, with no roots, that may be the problem. Certainly, with lots of rain, your foliage should be healthy, unless you have poor air circulation, which can cause leaf streak. Leaf streak is a fungal disease similar to rust that is caused by poor air circulation during moist/wet weather. It will cause ugly foliage with brown to yellow streaks, but will not kill the plant.
Good luck, Ed

If you think voles may be your problem, and I have lost several daylilies to them before I found out how to run them off, look for holes in the ground...you may see raised areas too. If they are there, get some castor oil from Walmart or a drug store and pour a little in the hole, and sprinkle it amoungst the daylilies the voles will leave.
kay

I think leaf streak is likely. I have had trouble with voles in the past but haven't seen evidence this year. My flowers are so gorgeous and I just hate those ugly leaves. Every plant needs divided, but lack of room (and energy, for that matter) prevents me from doing it. I do plan to try this fall, however. Thanks for the tip re castor oil. I'll try that next time I see a hole.

If it is leaf streak, you may treat by spraying with Cleary's 3336 50WP or Systhane 40WP. Treat every 2 weeks while symptoms persist.
Ed

I am having the same problem, I think. It started w/ my spiderwort (tradescantia), but now I am seeing brown leaves on my daylilies.
I do have a problem w/ voles, and have used some castor oil, but did not realize they would eat my daylilies too (I think they killed one of my butterfly bushes). I don't think it is leaf streak because my spiderwort eventually succumbs to it and dies. Also, I have rudbeckia plants and they slowly get sick and die. VERY annoying. I think I will broaden the area I covered w/ the castor oil, and try to make time to take a couple plants in to the extension office soon. Thanks, Brandy