There are various things that can cause chlorosis, in the daylily thread it was from the soil pH being too high (alkaline) and causing micronutrient (specifically either iron or manganese) deficiency. Burning bushes grow around here where the pH isn't to the point of being alkaline but is high enough that some daylilies get interveinal chlorosis. If it was high enough to cause problems with the burning bushes it most likely would be doing the same thing to daylilies there. In daylilies that type of chlorosis looks like this:
http://www.daylilies.org/ahs_d...
Can you post a close-up of the affected leaves? From the picture it looks like it is on the ends of the branches, is that consistent? I assume the soil isn't too dry? We get problems with shoot die back on burning bush here but I don't recall if what you're seeing may be a precursor - I will be going near some tomorrow and will check to see any are doing what yours are doing, or maybe someone else here is familiar with this.
