Symptoms and Signs
Plants with curly top are stunted because growth ceases. Plants turn yellow to bronze with purple-tinged leaves. Plants become stiff and soon die. Green fruit turns red, regardless of age.
Comments on the Disease
Beet curly top virus is only spread from plant-to-plant by the beet leafhopper, Circulifer tenellus. The virus and the beet leafhopper have very wide host ranges. Leafhoppers overwinter in the foothills bordering the Central Valley, migrating down into the Valley in late spring. Occurrence of the curly top disease is spreading; in some years it has caused almost complete crop loss in individual fields near the foothills.
Beet curly top virus is limited to the phloem, the food-conducting tissues of the plant, and the leafhopper must feed on the phloem in order to acquire and inoculate the virus to plants. Once acquired by the leafhopper, beet curly top virus is carried for the rest of the leafhopper's life, and thus long-distance spread is common. Infected plants are often widely scattered in a field; field margins are especially vulnerable because leafhoppers like to feed on plants that border bare soil areas.
Management
Dense stands of tomatoes apparently discourages visitation by leafhoppers. There is no genetic resistance in tomatoes to beet curly top virus. A statewide control program designed to control the beet leafhopper is practiced annually by spraying foothill areas where leafhoppers are congregated.