They're not going to kill your daylilies but they do disfigure the leaves. I assume your search took you to this AHS page:
http://www.daylilies.org/ahs_d...
No home-made spray is going to affect leafminers because they are protected from them inside the leaf. This is always a problem with leafminer pests of various plants. I would take off and destroy individual leaves with mines rather than cut a whole plant back.
