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Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 132 tomato plant one week after treatment application. Because of persistent TYLCV transmission by whiteflies, even one whitefly would be enough to raise concern. Uprooting TYLCV-infected plants and dimethoate application treatment were able to contain whitefly populations at the lowest level throughout the experimental season, albeit with minimal difference from plots treated with tomato-bean intercrop plus spraying bean rows with dimethoate (Figure 5.7). This situation could be explained by the fact that by uprooting TYLCV disease symptom-bearing plants (single foci), which are sources of inoculum, secondary infection or polycyclic disease epidemic is eliminated. It was noted that the first planting was preceded by a very dry season, which favoured whitefly population growth, as also observed by Mazyad et al. (1979) and reported by Henneberry and Castle (2001). It is also worth noting that March to July rains are usually heavier than August to December rains. For trial II (Figure 5.8), the trend was indicative of more favourable conditions for whitefly infestation. As such, treatment effect was noticeable after the second week. Furthermore, a less precise trend was observed in trial III (Figure 5.9) with limited treatment effects on whitefly populations, which could have been due to more frequent rainfall, as evidenced in Figure 5.3 and 5.6. However, within the first six weeks of November 1999 to February 2000 experimental period, whitefly populations rose drastically at two incidences, especially for the control monocrop. For monocrop plots 4 and 5 sprayed with dimethoate, the rise in whitefly populations was evident between the third to the sixth week, a situation similar to what is expected to happen when natural enemies are killed or when pests develop resistance to pesticides, but also the attractive vegetative nature of tomato plants at this stage. A similar trend was also observed, to a lesser degree, in plots where uprooting and dimethoate were applied, as well as in those with tomato-bean intercrop where bean rows were sprayed with dimethoate insecticide.
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 133 Table 5.5: Mean number of whiteflies trapped by Kubwa trap per plant per plot in trial I, II and III (df = 13; F 18, 20; p = 0.001) Trial I (March- July 1999) Trial II (August – Nov. 1999) Trial III ( Nov. 1999 – Feb. 2000) Ranked treatments Whitefly mean count per plot Tomato monocrop x uprooting Tomato monocrop Monocrop x dimethoate Monocrop x uproot x dimethoate Tomato-beans intercrop Intercrop x dimethoate on beans 29 27 23 22 20 20 Ranked treatments Whitefly mean count per plot Tomato monocrop x uprooting Monocrop x dimethoate Intercrop x dimethoate on beans Tomato monocrop Tomato-beans intercrop Monocrop x uproot x dimethoate 0.23 0.17 0.17 0.11 0.04 0.02 Ranked treatments Whitefly mean count per plot Intercrop x dimethoate on beans Monocrop x dimethoate Tomato monocrop x uprooting Tomato monocrop Monocrop x uproot x dimethoate Tomato-beans intercrop SE 0.30 0.30 0.30 CV 0.02 0.02 0.02 0.21 0.20 0.18 0.18 0.18 0.16
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Incidence, Distribution and Charact
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Charles SSEKYEWA Incidence, Distrib
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CONTENTS 1 CHAPTER 1...............
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ACKNOWLEDGEMENT The following perso
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vii 7 mosaic virus (CMV), Alfalfa m
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ix 9 Consequently, our findings con
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SAMENVATTING Tomaat is een economis
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xiii 13 Beide genhomologie percenta
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xv 15 dit onderzoek geven ook aan d
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LIST OF TABLES xvii 17 Table Page 1
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ACRONYMS AND ABBREVIATIONS xix 19 A
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Abbreviation Word in full PCR Polym
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