The Daylily leafminer is a recent pest from Asia. It was first detected in 2006 but is now spread through much of the Southeast including North Carolina. I spotted some last week on a trip to Georgia. This fly lays its eggs in day lilies and the larvae produce relatively straight, vertical mines. Pruning infested leaves will help prevent the larvae from maturing and infesting new leaves. I do not know of any formal efficacy tests on this pest but other material targeting leafminers such as imidacloprid and pyriproxifen should help. A recent article about this pest is in American Nurseryman.