Causal Agent:
Tomato Yellow Leaf Curl Virus (TYLCV).

Vector:
Whitefly (Bemisia tabaci)

Distribution:
Africa, Dominican Republic, Mediterranean area, Southeast Asia, and The Middle East

Symptoms:
Plants infected at an early stage can be stunted, develop erect branches, and have small chlorotic leaflets which cup and twist upward. Severely affected plants generally do not set fruit. Although less severe, yellowing of leaflets, leaf cupping, failure to set fruit and flower abortion can also be common when infection occurs at a later stage. Fruit that has set before the plants become infected often ripens normally.

Conditions for Disease Development:
The virus is acquired from infected tomatoes or several solanaceous weeds by the larvae of the sweet potato whitefly and is transmitted in a persistent manner by the adult whitefly into a tomato crop. Secondary spread of the virus in a field is common. The virus is not mechanically transmitted so it is unlikely that it will be spread from infected to healthy plants by workers. Severe outbreaks of the disease are often associated with large populations of the whiteflies.

Control:
The use of tolerant varieties greatly reduces losses from this disease, as does the removal of solanaceous weeds which are in the vicinity of the tomato crop. Applying mineral oil on a regular basis may help slow the rate of spread of the disease by reducing the acquisition and transmission of the virus by the whitefly. Covering plant beds with yellow plastic mulch which attracts the whiteflies and then spraying on a regular basis with insecticides has proven effective in some areas.

Leaf yellowing and curling.

Severe leaf yellowing and curling.