Incidence, Distribution and Characteristics of Major Tomato Leaf ...

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases
Although the above methods are sometimes used, there are a number of disadvantages
associated with them. For example, turning leaves and taking leaf sample measures gives
an estimate of whiteflies on the plant, but these methods are very tedious and inefficient
because adult whiteflies fly away upon turning the leaf and they seldom oviposit on
tomato, in which case nymphs are not even available for counting. Consequently, there is
a need to develop a more efficient sampling tool that would be able to provide whitefly
population data for single tomato plants in the field, as was provided for in this study.
2.1.4 Principles of Tomato Virus Disease Management
According to Palumbo et al. (2001), cultural and biological pest management tactics
provide the best options for controlling B. tabaci and overcoming the problem of
insecticide resistance. As such, various cost effective measures have been reported for
controlling tomato virus diseases. They include cultural practices, vector manipulation,
inoculum source elimination or phytosanitation, cross-protection, use of resistant
varieties or even transgenic plants, and virus or vector exclusion (Matthews, 1991; Dent,
1991; Beachy, 1997; Mason et al., 2000; Hilje et al., 2001; Lapidot and Friedmann, 2002;
Greer and Dole, 2003; Rubio et al., 2003; Yang et al., 2004; Mutwiwa et al., 2005; de
Castro, et al., 2005; Kumar et al., 2006; Zilahi-Balogh et al., 2006; and Fuentes et al.,
2006).
2.1.4.1 Integrated Vector Manipulation (IVM)
IVM is the application of a number of vector control options at the same time. IVM plays
a significant role in control of many viral diseases. Previous reports (Simons et al., 1959;
Simons et al., 1980; Palumbo et al., 2001; Greer and Dole, 2003) indicated that use of
either pesticides, or mineral oils, barriers, insect traps, reflective mulches such as white
polythene and aluminium foils, insect parasites, predators, and male sterility led to
management of insect pests such as aphids, thrips, and whiteflies, which are also virus
vectors. There are also biological control options, though they are mostly used in screen
houses. Whiteflies are parasitised by several wasps such as Encarsia formosa and
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