Diseases Caused By Phytoplasmas

Beet Leafhopper-Transmitted Viresence Agent

Leaves of infected plants are reddish purple with mild chlorosis. Infected plants often bolt prematurely. Flower parts are malformed; petals that would normally be white are green, and the flowers proliferate to form multiple, compound, leafy umbels. Diseased plants have unmarketable roots that are thin, woody, and hairy.

Aster Yellows Phytoplasma

Leaves of infected plants are twisted, stunted, and yellow. Leaflets may be reduced to short scales. Flower parts are severely distorted and malformed; umbels are stunted and yellow green. Most infected plants develop a dense cluster of dwarfed, chlorotic, upright, adventitious shoots. Infected plants have long, thin roots with increased lateral rootlet development.

The beet leafhopper-transmitted virescence agent is transmitted by the beet leafhopper, Circulifer tenellus. Aster yellows phytoplasma is transmitted by several species of leafhoppers. Both phytoplasmas have wide host ranges. The level of infection in carrot fields is dependent on the population of vectors. Disease incidence may be greater if carrots are planted near areas where weeds and other plants provide a reservoir for the phytoplasmas and their vectors.

There are no effective controls for these diseases.