Aster Yellows

Aster yellows symptoms and severity can be highly variable depending on the strain of the pathogen, the age of the plant when infected, and other factors. Celery plants are usually severely stunted and yellow. Inner petioles are characteristically short, yellow to white, and moderately to severely curved and twisted. On older plants, petioles become brittle, and the epidermis and underlying tissues may crack and peel. In later stages of the disease, the heart of the plant turns brown and may decay.

Note that Fusarium yellows can cause similar stunting and yellowing. However, Fusarium yellows causes distinct vascular browning in the roots and crowns and does not cause petiole deformities.

Although aster yellows has virus-like symptoms, it is actually caused by the aster yellows phytoplasma, a single-celled organism that, like bacteria, lacks a nucleus and is therefore classified as a prokaryote.

Aster yellows is transmitted to crops by leafhopper insect vectors. Leafhoppers acquire the pathogen while feeding on infected plants. The pathogen may persist in overwintering leafhoppers from one season to the next. Major weed hosts of the aster yellows pathogen include broadleaf plantain, buckhorn plantain, dandelion, horseweed, pineappleweed, Russian thistle, sowthistle, wild asters, wild chicory, and prickly lettuce.

When leafhoppers migrate from pasture or non-crop land to vegetable fields, or when drying vegetation drives leafhoppers from foothills and other areas, the insects encounter celery and other crops and transmit the phytoplasma during feeding. Therefore, significant aster yellows outbreaks almost always occur in fields near pastures, rivers, ditch banks, foothills, and weedy non-crop land. Because of fluctuations in both the numbers and flight patterns of leafhoppers and the amount of infected reservoir plants, incidence of aster yellows varies greatly from year to year.

Aster yellows is difficult to control, in part because of the extensive host range of the phytoplasma. Over 300 species of food, forage, ornamental, and weed plants are susceptible. Weed management alone will not control aster yellows. Avoid planting celery in fields near known phytoplasma and leafhopper reservoirs.

Use cultural controls in a certified organic crop.

There are no pesticide controls for the aster yellows phytoplasma. Insecticides alone will not prevent leafhopper transmission of the pathogen.