Aster Yellows

Need to know

  • Aster yellows is a disease that can cause bizarre symptoms on many plants.
  • Typical symptoms of aster yellows include veins that turn pale, yellowing of new leaves, abnormally bushy growth, deformed flowers, and stunting.
  • Symptoms are more pronounced in hot weather, a plant can be infected without showing any symptoms.
  • No treatment is available to save a plant infected with aster yellows.

Overview of aster yellows 

Image of aster yellows symptoms on coneflower.
Aster yellows symptoms on a coneflower. Small deformed leaves have replaced part of the flower head.

Aster yellows is a 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.

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 the 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.

Signs of aster yellows

No signs are visible, specialized nucleic acid testing is required to confirm this fastidious bacteria-like organism causing the symptoms.

Disease cycle of aster yellows

Symptoms are more pronounced in hot 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 your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's 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.

Want to submit a sample? select special testing on our submission form, and follow the foliar instructions at Submitting Trees and Shrubs page. 

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. Always inspect new plants for symptoms before you purchase them or plant them in the garden.

Last reviewed:
January 2022

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 1, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.