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Aster Yellows of Annuals and Perennials

Aster yellows is most commonly found on chrysanthemum, aster, daisy, marigold, and petunia, but it occurs on many other species as well. Affected plants are easy to identify: they appear yellowish, stunted, stiff, erect, and bushy. The flowers may be deformed, with partially or totally green, leafy petals. The plants look like they have been infected by a virus.

Aster yellows is a disease caused by a phytoplasma (formerly known as mycoplasma). Phytoplasmas are pathogens similar to fungi, bacteria, and viruses--specifically, an organism between a bacterium and a viral pathogen. The important things to remember about phytoplasmas are that they are transmitted by sucking insects (in the case of aster yellows, by leafhoppers) and they cannot be cultured in a laboratory.

Because the pathogen can be transmitted by leafhoppers, control measures include destroying all affected plants when they are first seen, eliminating broadleaf weeds, and, of course, buying symptom-free plants. Spraying regularly to keep leafhoppers from feeding may be beneficial in a commercial setting.

We do not see many aster yellows samples in the lab. Part of the reason is that such plants are rogued before they reach retail outlets. Symptoms are easy to identify by comparing the suspect plant to disease-identification photos. The pathogen cannot be cultured in the lab, so sending a sample to the Plant Clinic is not necessary. For a detailed description of aster yellows, consult Report on Plant DiseasesNo. 903.

Author: Nancy Pataky


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