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.
Biological control is often possible.
One must identify the problem and then find the solution. The damage must be attributed to a specific cause and then rectified. Integrated pest management is a term that is gaining popularity. This does not preclude using sprays although a spray is chosen with minimal impact outside of the knocking down a specific pest. It is a temporary solution.