Cause Candidatus Phytoplasma asteris, formerly referred to as a mycoplasma-like organism (MLO), which is spread naturally by a leafhopper insect. Leafhoppers may take several days to acquire the phytoplasma while feeding on infected plants. It takes several more days or up to a month before they can spread the pathogen to healthy plants. Once in the plant the organism is restricted to the phloem where it can be picked up by other leafhoppers. The disease is common to many plants, particularly those in the composite group, including chrysanthemums and asters.
Symptoms Very noticeable when the flowers produced on chrysanthemum are green (virescent or leaf-like) instead of the normal color for the cultivar. Sometimes the flowering stem's upper branches are thin, pale or yellowish, and more upright than usual. A number of thin, weak shoots bearing tiny leaves may rise from the base of the plant.
Cultural control
- Remove and destroy infected plants.
- Control leafhoppers. See the PNW Insect Management Handbook.
- Reflective mulches to discourage leafhoppers.
- Use fine mesh nets or screens to exclude leafhoppers in the greenhouse.
- Heat treatment at 86°F to 99°F for several weeks.
Reference Lee, I-M., Gundersen-Rindal, D.E., Davis, R.E., Bottner, K.D., Marcone, C., and Seemüller, E. 2004. 'Candidatus Phytoplasma asteris', a novel phytoplasma taxon associated with aster yellows and related diseases. International journal of systematic and evolutionary microbiology 54:1037-1048.