Aster Yellows of Annuals and Perennials | |
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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.
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| Author: | Nancy Pataky |
