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.
Strategies to address plant virus diseases need to include farmlevel
training to increase farmers' awareness and knowledge about
plant viruses, including disease identification, epidemiology and
management. Being able to distinguish symptoms of virus infection
from other diseases, and knowledge that most viruses are transmitted
by insect vectors (mainly whiteflies, aphids or thrips) may
encourage farmers to control insect populations and avoid the
unnecessary use of fungicides and other pesticides ineffective
against virus diseases. Yet, insect control must be practiced before
the symptoms of virus diseases have started appearing in the
cropdwhich requires a massive leap in farmers' knowledge about
the epidemiology of viruses. Careful monitoring of vector populations
for disease control is not practiced currently; for instance,
no farmers in our sample used blue or yellow sticky traps, a simple
method commonly employed for vector population monitoring in
other counties, nor did input shops sell such traps.
Symptoms of fungal, bacterial and viral diseases can be
confusing even for trained experts to identify, and may occur in
mixtures, further confounding correct identification. This study
could have been stronger if it had been combined with a diagnostic
survey to more accurately determine the incidence and severity of
Table 6
Pesticide use practices, average per household.
Tomato Chili Mungbean
THA VNM INeTN THA VNM INeTN VNM INeTN
Farmers using synthetic pesticides (%) 99 99 97 93 100 83 100 31
Pesticide products applied in most recent cropping cycle 5.0 5.1 4.0 1.4 5.9 2.2 1.9 0.7
Median quantity of active ingredients used (kg/ha) 34.9 4.3 3.0 0.1 2.1 0.4 0.2