Cause Candidatus Phytoplasma asteris formerly referred to as a mycoplasma-like organism. This organism has a wide host range. Some of the 170 plant species that may be affected are: anemone, calendula, chrysanthemum, coreopsis, cosmos, delphinium, daisy, marigold, gladiolus, golden-glow, petunia, phlox, and statice. Many vegetables also are affected including carrot, squash, and tomato. The main vector of this organism is the six-spotted leafhopper. The phytoplasma multiplies in the insect; however, there is a delay of 10 days or more after the insect feeds on a diseased plant before it can infect a healthy specimen. There is no transmission by seed or through insect eggs. Once in the plant the organism is restricted to the phloem where it can be picked up by other leafhoppers.

Symptoms Vein clearing, yellowing, and distortion of new leaves can occur. Plant is stunted but has stiff, erect appearance and many shoots. Affected plant may not produce flowers; if present, they are usually a greenish-yellow color and leaf-like.

Cultural control

  • Plant more thickly than usual and rogue out affected plants.
  • Shading asters reduces leafhopper feeding and hence disease transmission.
  • Fine mesh nets or screens can be used on greenhouse vents and doors to prevent leafhopper entry.
  • See PNW Insect Management Handbook for more information on leafhopper control.
  • Control weeds in and near plantings.

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.