If the blooms on your coneflowers look distorted, they may be plagued with aster yellows, a viral-like disease that is transmitted by insects that feed on their sap. Plants with aster yellows are “infected” with a phytoplasma in their phloem that multiplies, causing deformed flowers and odd tufts of growth inside the blooms. This may also cause yellowing of leaves, but is hard to identify by that symptom alone.