Aster yellows is a serious, chronic disease that occurs throughout North America and may affect over 300 species of plants in 38 families including a number of vegetables such as carrots, potatoes, lettuce, endive, and artichokes. However, as its common name implies, aster yellows occurs most often on members of the aster family (Asteraceae) and coneflowers are particularly susceptible.
Of course, coneflowers (Echinacea spp.) have long been a favorite in Ohio landscapes and naturalized areas because of their beauty and attractiveness to pollinators of all sorts. Unfortunately, aster yellows can turn a longstanding planting of coneflowers into a collection of stunted and weirdly deformed plants.
The disease is caused by a phytoplasma. All known forms of these small, specialized bacteria are plant pathogenic and they infect plant phloem tissue. Phytoplasmas are naturally spread from plant to plant by sucking insects, particularly leafhoppers.
Symptoms of aster yellows include chlorotic, curled foliage; stunted stems; and bizarrely distorted flower parts. Flower petals may appear as a ring of tiny greenish-yellow spoons arrayed around the base of highly deformed cones. Cones may appear as tightly clustered rosettes. This symptom is sometimes mistaken for damage caused by the eriophyid mite commonly known as the Coneflower Rosette Mite and vice versa.
Aster Yellows wreaks havoc on all parts of the plant. There are no sprays that will suppress the disease and once plants become infected, they remain both infected and infectious which means they serve as a constant reservoir of the phytoplasma to be spread to other plants. Thus, sanitation is key to managing the disease. All parts of the plant including the root system must be removed and destroyed. As with all phytoplasmas, the aster yellows pathogen cannot survive outside of the plant so the bacterium should not remain infectious in the soil.