Only a minority of the farmers in this study can identify viruses as the causal agent of specific disease symptoms. Even fewer know the role of insect vectors in the spread of plant viruses, which confirms the earlier study of Nagaraju et al. (2002) in Karnataka, who found that only 2% knewthat the tomato leaf curl virus disease was transmitted by whiteflies. However, farmers in Tamil Nadu generally had more knowledge about plant viruses than farmers in Thailand and Vietnam, as extension services and seed companies had paid attention to this issue.