One of garden club members ID this as a disease called asters yellows:
Aster yellows on purple coneflower showing a distorted flower head and greenish, petaloid parts.
Aster yellows is caused by a microscopic pathogen called a phytoplasma. This is a one-celled, organism closely related to bacteria that infects a number of annuals, perennials, grasses and vegetables causing growth malformations and various color changes in plant parts. The phytoplasma is transferred from plant to plant via insects that suck the sap from infected plants - notably the aster leafhopper. Leafhopper migrate for long distances from overwintering sites in the south and continue to propagate the disease each season. Aster yellows affects over 300 hosts including some of the most common garden plants and vegetables.
