Recently, the Home and Garden Information Center (HGIC) has been receiving photos of coneflowers (Echinacea purpurea) that are malformed and green. The plants are infected with aster yellows, a bacterial phytoplasma (a type of bacterium that does not have cell walls). Aster leafhoppers (Macrosteles quadrillineatus) carry the pathogen and infect the plant tissue when they feed on it. They are small olive-green to tan insects with wedge-shaped bodies. Adults are 1/8 in length and have three pairs of spots on their heads.
Coneflowers (Echinacea purpurea) infected with aster yellows will have malformed and green flowers.
Barbara H. Smith, ©2024 HGIC, Clemson Extension
Aster leafhoppers (Macrosteles quadrillineatus) carry the aster yellows pathogen, infecting the plant tissue when they feed on it.
Whitney Cranshaw, Colorado State University, Bugwood.org
The aster yellows bacteria will systemically move into the phloem (part of a plant’s vascular system that transports sugars and other organic compounds produced from photosynthesis from the leaves of a plant to the roots), infecting all the plant’s tissues from the roots to the leaves.
White Swan coneflowers (Echinacea purpurea ‘White Swan’) are showing different stages of aster yellows infection.
Barbara H. Smith, ©2024 HGIC, Clemson Extension
Unfortunately, once a plant is infected with aster yellows, there is no cure. The only option is to completely remove any plants showing symptoms of aster yellows, bag them up and put them in the garbage. The infected plants can be buried in a compost pile, but make sure they are completely covered with compost or soil so insects can’t feed on the infected tissue. Once the plant is dead, the aster yellows phytoplasma will not survive.
Aster yellows can infect over 300 species of herbaceous and woody plants. Usually, it’s commonly noticed in coneflowers, black-eyed Susans (Rudbeckia sp.) or zinnias (Zinnia elegans). When an aster leafhopper feeds on an infected plant, it will ingest the bacterium and spread it to other plants.
Zinnia flowers that are deformed from an aster yellows infection.
Barbara H. Smith, ©2024 HGIC, Clemson Extension
Symptoms
- Distorted flowers will have deformed, green-colored petals.
- The shoots, leaves, or flowers emerge from the same point, forming a witches’ broom.
A purple coneflower exhibiting a witches’ broom deformity.
Ginger Long, ©2024 HGIC, Clemson Extension
- The plants are yellow and stunted.
As the disease progresses, all the flowers and foliage are affected by aster yellows.
Barbara H. Smith, ©2024 HGIC, Clemson Extension
- Finally, the plant will wilt and die.
In addition to removing the infected plants, weed control around your landscape is important. Weeds can serve as sources of infection as they can harbor aster leafhoppers and the aster yellows pathogen.
