Tomato yellow leaf curl virus



Tomato yellow leaf curl virus is not seed-borne. It is only transmitted by the whitefly, Bemisia tabaci, which is commonly found in tropical and sub-tropical regions, and in greenhouses in temperate areas.

Symptoms
Plants become severely stunted and shoots become erect. Leaflets are reduced in size and pucker. Leaflets curl upwards, become distorted, and have prominent yellowing along margins and/or interveinal regions. Flowers wither.

Chemical
Chemical control methods include the application of systemic insecticides as soil drenches or regular sprays during the seedling stage to reduce the population of the whitefly vector. A second application may be necessary to control adults that have emerged from the egg and nymph stage since the application of the first spray. Rotation of insecticides may be necessary to prevent the development of resistance in the vector. However, chemical control may not be effective in areas where disease incidence is high. Other methods include a 1% soap solution carefully applied to the leaf undersurface to control the adult vector. Care should be taken to avoid development of phytotoxicity if spraying occurs during very high temperatures. Oil sprays may also be effective in reducing levels of infestation. Neem tree seed extracts control young nymphs, inhibit the growth and development of older adults, and reduce egg-laying by adults.

Prevention
Inter-planting of tomato with ‘bait’ plants such as cucumber may be useful for control of this virus but other viruses such as cucumber mosaic virus may increase in importance. The ‘bait’ plants are then sprayed with an insecticide.