So sorry about the weed invasion and wish I had an easy solution, but the answer to getting rid of grassy weeds embedded in daylilies is to dig up the entire clump of daylilies. Once you have the daylily clump out of the ground, you can divide it into smaller sections for replanting or to give some away. This division of the daylily clump means you will be able to thoroughly clean off the roots using a strong jet of water and remove every last trace of the invading grass's roots. Then, before you replant into the same area, dig up the soil to look for any more small pieces of root. This physical removal of the weed roots is the most efficient way to rid yourself of a very invasive weed. You can do this daylily division, cleaning and replanting in the fall or early spring.  Take your time, dig in and imagine that feeling of satisfaction next summer when the daylilies are blooming without weeds. Keep growing, Marianne Binetti