Overview of aster yellows
Aster yellows is a fairly common disease that can cause bizarre symptoms on a wide variety of plants. The disease can be found on hundreds of plants, including many flowers and vegetables, such as coneflower, daisy, marigold, zinnia, snapdragon, chrysanthemum, tomato, carrot and lettuce.
Signs and symptoms of aster yellows
Typical symptoms of aster yellows include veins that turn pale, yellowing of new leaves, abnormally bushy growth, deformed flowers, and stunting. Infected plants often have a stiff, upright appearance, with branches joining the stem at narrow angles. The appearance of this disease varies with the host plant. On coneflowers, the most typical symptom is replacement of flowers by tufts of small, green, deformed leaves. Infected carrots roots may be excessively hairy and bitter, and in lettuce, inner leaves may be curled and twisted, whereas outer leaves do not develop fully and have pink or tan spots. On onion, leaves are small, twisted and yellow.
Disease cycle of aster yellows
Symptoms are more pronounced in hot weather, and in cool weather a plant can be infected without showing any symptoms.
Aster yellows is caused by a tiny organism called a phytoplasma, similar to a bacterium. The phytoplasma is carried from plant to plant by aster leafhoppers, which feed on the sap of the plants.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us
Management of aster yellows
No treatment is available to save a plant infected with aster yellows. Aster yellows is best managed by removing infected plants from the garden to minimize spread. Management of the insect vector is not usually feasible in a home garden.
See this article for information about aster yellows.