Aster yellows

Aster yellows is a disease caused by Aster yellows phytoplasma affecting several genera of herbaceous plants, primarily in the Aster family. The aster leafhopper vector, Macrosteles quadrilineatus, moves the aster yellows phytoplasma from plant to plant.

Symptoms
There are a range of characteristic symptoms which vary with the phytoplasma strain, timing of infection, plant species, temperature, age, and/or size of the plant. The symptoms can be mistaken for herbicide damage.

Symptoms include vein clearing until the entire leaf becomes chlorotic, stunting, deformation, virescence (greening of flowers), phyllody (development of leaf-like flower petals), reddening of foliage, reduced root system, and sterility. Aster yellows does not typically kill perennial host plants.

Carrot
Initial vein clearing and chlorosis, followed by production of many adventitious shoots, with the tops looking like a witches’-broom. The internodes of such shoots are short as are the leaf petioles. Young leaves are smaller and dry up while the petioles of older leaves twist and break off. Any remaining older leaves turn bronze or red late in the season. Floral parts are deformed and roots are smaller, abnormally shaped and have woolly secondary roots. The carrot roots are predisposed to soft rots in the field and storage and taste unpleasant to the consumer.

Treatment
No treatment is available to save a plant infected with aster yellows. It is best managed by removing infected plants from the garden to minimize spread.

Prevention
Management of the insect vector is not usually feasible in a home garden.