Symptoms and Signs
Symptoms of aster yellows includes yellowing, dwarfed or distorted foliage, and the abnormal production of shoots. Flowers may not develop normally and are often replaced by green leafy structures. Aster yellows symptoms may closely resemble those caused by viruses.
Comments on the Disease
Aster yellows is caused by a microscopic organism called a phytoplasma. Phytoplasmas are closely related to bacteria but are somewhat smaller in size and do not have a rigid cell wall.
Initially, the aster yellows phytoplasma was thought to be a virus. Phytoplasmas are vectored by leafhoppers, plant hoppers, and psyllids and invade the phloem of infected plants. The aster yellows phytoplasma is vectored by leafhoppers, in which it can multiply. It has a very wide host range, which includes many ornamentals, food crops, and weeds.
Aster yellows is difficult to control, in part, because of the extensive host range of the pathogen. Over 300 species of food, forage, ornamental, and weed plants are susceptible. While weed management should be practiced, this will have little effect on aster yellows. Plant pathogen-free plants and use good sanitation. Remove and destroy infected plants. There are no chemical controls for the aster yellows phytoplasma. Control of the leafhopper vector could reduce transmission of the phytoplasma.
EXAMPLES OF HOSTS OF ASTER YELLOWS PHYTOPLASMA
|Ornamental hosts||Crop plant hosts||Weeds and native plant hosts|
|alyssum, calceolaria, calendula, China aster, chrysanthemum, cineraria, daisies, delphinium, gladiolus, gloxinia, gypsophila, larkspur, petunia, statice, sweet william, tagetes, veronica, zinnia, and many others||buckwheat, carrots, celery, lettuce, onion, parsley, parsnip, potato, safflower, spinach, tomato, and many others||California poppy, dandelion, plantain, and many others|