Mona,
Check at your local Lowes' or Home Depot. They should have a systemic insecticide for ornamental plants in the garden center. Orhto used to make one called Othene and I know Spectracide makes one I just can't remember the name. You'll have to read the labels to see which is ok for daylilies. Sevin will kill the ones you actually hit, but any that are down inside the fans will just keep sucking the life out of your plants. I try to be as organic as possible, but with the outbreak your describing I think you may need to be more ruthless. Good luck.