Efficacy of Aqueous Extracts from Syzygium aromaticum, Tephrosia vogelii, and Croton dichogamus against Myzus persicae on Brassica oleracea in Northern Tanzania

The effectiveness of 1, 5, and 10% w/v of aqueous extracts of Croton dichogamus, Tephrosia vogelii, and Syzygium aromaticum and their mixture (2.5 and 5%) was evaluated against Myzus persicae on Brassica oleracea under field conditions. The synthetic chemical insecticide, chlorpyrifos, was used as positive control, and water and water plus soap were used as negative controls. Aqueous extracts significantly ( P ≤ 0.05 ) lowered M. persicae population compared with negative controls. The 5% of the aqueous extract from mixed plants and 10% of each plant used in this study significantly ( P ≤ 0.01 ) reduced aphid, M. persicae population comparable to chlorpyrifos in 2019 and 2020. However, the 1 and 5% concentrations of aqueous extracts of C. dichogamus, T. vogelii, and S. aromaticum and 2.5% of aqueous extracts from the mixed plants significantly lowered the population of M. persicae compared with negative controls in 2019 and 2020 wet seasons. The weekly observations revealed that, at weeks 1, 2, 3, 4, and 5 after application of treatments, the population of M. persicae differed significantly ( P ≤ 0.05 ). Also, the aqueous extracts from the mixed plants at 5% concentrations significantly ( P ≤ 0.01 ) reduced M. persicae population as compared with other treatments. It was as effective as synthetic chemical pesticide (chlorpyrifos). Also, 1 and 5% of C. dichogamus, T. vogelii, and S. aromaticum and the 2.5% of aqueous extracts from the mixed plants significantly reduced the population of M. persicae for all 6 weeks of study compared with negative controls. Therefore, these pesticidal plants can be recommended to smallholder farmers for the control of M. persicae in B. oleracea crops.