I have 5 coneflower plants in different locations and they are all affected by the same problem. I started noticing holes in all of the foliage with some of the plants' foliage disappearing almost completely. Some of the foliage is also withered and blackish gray. I have noticed many very small black catepillars, about a half inch long, on several of the plants. The plants range in age from several years to one year old.
Certified GKH Gardening Expert
The caterpillars are likely the cause, but which they are I cannot tell without a picture. However, all caterpillars are treated the same. This article will help: