Aster Yellows (Misshapen Coneflowers)
Green petals, misshapen flowers, twisted, and distorted leaves that turn yellow or red and tufts of white hairy roots on carrots are symptoms of aster yellows.
This disease attacks nearly 300 plants including coneflowers, Rudbeckias, coreopsis, marigolds, and other members of the aster family. Lettuce, carrots, and potatoes are just a few of the susceptible vegetables. Aster leafhoppers are the carriers of the phytoplasma (bacterium-like organism) that causes this disease and these symptoms. The leafhopper feeds on an infected plant, ingests some of the disease organism, and injects it into the next plant it feeds upon.
Though the disease is usually not fatal removing infected plants reduces the source of disease. This includes infected weeds like dandelions.
Removing infested plants and using insecticidal soap to control the leafhoppers that carry the disease may help reduce its spread.
A bit more information: Though infected plants usually don’t die this disease can overwinter in the crowns of perennial plants and serve as a source of infection the following year. And keep in mind controlling leafhoppers can be difficult since they are constantly moving in and out of the garden.