The reason I asked about hot dry sunny weather is because some of your problem looks like leaf scorch, see the top picture here:
http://hyg.ipm.illinois.edu/pa...
Some looks like leaf streak, and it may be that one led to the other because leaf streak needs an injury of some kind to infect. There also may be a nutritional issue going on but it's hard to be sure, some of the other leaves look to be an uneven green.
It is actually quite difficult to identify some daylily problems visually, quite often the only way to be sure what something is requires a diagnostic lab and most of us aren't going to bother with that unless it is a serious problem causing the demise of numerous plants. So we have to try and piece together the possibilities then go through a process of elimination.
