3.3. Farmers' knowledge and perceptions of plant viruses
During the survey, farmers were shown photos of virus disease
symptoms without the researcher telling them that this was a virus
disease. The great majority of farmers recognized these symptoms
as problems they also had in their own fields (Table 5). Generally,
the farmers selected photos of more than one virus family, with
chili farmers in Vietnam selecting three different virus families on
average.
Asked what could be the cause of these disease symptoms, most
farmers in Thailand and Vietnam were unaware that these were
caused by a virus. Of the Thai chili farmers, only 8% identified the
problem as caused by a virus, whereas in Tamil Nadu, 49% of tomato
and 58% of chili farmers were aware that the disease symptoms
were caused by a plant virus. Private seed companies and government
extension services in Tamil Nadu, India have been active in
educating farmers in this respect, while no such activity was conducted
in the other countries. It is noted that it is not entirely wrong
if farmers identified the disease symptom as being an insect
problem.
Asked to indicate the severity of the problem on a scale from 1
(not a problem) to 5 (very severe) for the most recent crop and two
previous crops, farmers in Tamil Nadu assessed problems with
plant viruses as very severe for all three crops. Tomato farmers in
Thailand also assessed it as a severe problem. Farmers in Thailand
and Tamil Nadu indicated that the severity increased during the
three most recent times they grew the crop. However, no such
upward trend appeared for any crop in Vietnam and the average
score that farmers gave for their most recent crop was 2.1 for tomato
to 2.5 for mungbean.
Very few farmers in Thailand and Vietnam knewthat insects can
transmit plant viruses. In tomato production, only 16% of the Thai,
0% of the Vietnamese, and 31% of the Tamil Nadu farmers associated
the spread with whiteflies, thrips or aphids. These insects are the
vectors for the most common viruses of these crops in the survey
areas. In contrast, 54% of the tomato farmers in Thailand thought
that the disease (presented in the photograph and recognized by
experts as caused by a tomato leaf curl virus, a whitefly-transmitted
begomovirus) was spread through soil or water, while 84% of thefarmers in Tamil Nadu thought it could spread by the wind. It must
be noted that there is some logic to this latter perception, since
vector insects such as whiteflies can be carried long distances by
the wind. Only chili farmers in Tamil Nadu (64%) mentioned thrips,
whiteflies or aphids as a disease transmitter.
In Tamil Nadu farmers have started using certain biopesticides
claimed to be effective against virus diseases. In some cases they
mixed the biopesticides with synthetic pesticides (such as monocrotophos
or imidacloprid), although government extension services
and agricultural departments do not recommend this. It was
also noticed that input dealers provided so-called “combo kits”
comprising an insecticide, fungicide and a biopesticide to be
applied in one spray, regardless of the compatibility of these
compounds or the pest infestation. Private farm magazines also
publish numerous articles in local languages vociferously advocating
the use of biopesticides against plant viruses, without proper
scientific studies. Government agencies (agricultural and horticultural
departments) provide no practical solution other than
uprooting and destroying virus-infected plants. The farmers tend to
rely upon the input dealers and their suggestions.