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

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases
Eretmocerus spp., as well as predators like lacewing and coccinelids (Zalon et al., 2003).
However, concentrating on vector control is not always very effective since some vectors
transmit viruses in a persistent manner (Green, 1991; Gianessi et al., 2003), so that even
at very low densities, some vectors are effective in transmitting viruses. Moreover,
transmission of non-persistent viruses takes place quickly and readily, and is often
performed by vectors that visit, but do not establish their colonies on the visited crop.
According to Perring et al. (1999), no one method of control is likely to keep crops free
of vectors and virus infections.
2.1.4.1.1 Crop Sanitation
A number of cultural practices have been reported to reduce incidence and severity of
viral diseases. These include elimination of inoculum sources by removal of infected
plants and alternative hosts. Chan and Jeger (1994), while working with an analytical
model of plant virus disease dynamics with uprooting and replanting, found that in
sparsely planted crops intensive uprooting only was able to eradicate virus diseases. Cho
et al. (1989) reported that removing TSWV-infected crop plants, weeds and alternative
hosts, in an overall integrated management package, helped to control viral diseases.
Lloyd et al. (1974) were able to eliminate banana viruses by use of virus-free planting
material obtained by thermal therapy and tissue culture. Other effective methods reported
are debris removal from the field, disinfection of support trellises before re-use, crop
quarantine measures executed for incoming seeds, and crop rotation (AVRDC, 1985;
Green and Kim, 1991); use of skimmed milk foliar sprays (Black et al., 1991; Green et
al., 1991); application of antiviral agents like cytovirin (Simmons 1959), and treatment of
tomato seed with trisodium phosphate for 1 hour (Broadbent, 1965 and 1976).
2.1.4.1.2 Cultural Control
There are a number of cultural control measures, such as close plant spacing to
compensate for yield losses through diseased plants, use of mulching and intercropping
with nitrogen fixing cover crops like Lablab purpureus L. (Cohen et al., 1974). Greer and
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