You may be subject to fines for violation of federal law. This is true for herbicides as well as insecticides. If you examine an herbicide package containing trifluralin as the active ingredient, you will see that daylilies are absent from the list of plants for which it is approved. I assume this difference in the labels in purposeful. As with any pesticide, it is necessary to use the chemical following directions and to check the results.
Cultivars differ in sensitivity to chemicals.
Even a chemical like 2,4-D will only harm SOME daylily cultivars. The roadside fulva will not even notice a treatment with 2,4-D. Integrated Pest Management When determining a course of action, you first need to determine the source of the problem. One of the simplest ways to identify pests is to use a sticky card to collect bugs in your garden. It is possible to buy a brochure to identify bugs stuck on sticky cards. When I choose to use a chemical spray, I choose the mildest one that will slow down the epidemic.