The efficacy of two bio-rational pesticides on insect pests complex of two varieties of white cabbage (Brassica oleracea var. capitata L.) in the coastal savanna region of Ghana

摘要

Insect population count and yield were used to determine the effectiveness of two bio-rational pesticides -a commercial formulation of Pieris rapae granulosis virus and Bacillus thuriengensis, Bypel 1 (PrGV + Bt) (1.5 g/l w/v) and aqueous neem kernel extract (ANKE) (50 g/l w/v), on the insect pests complex of two cabbage varieties, KK cross and Oxylus for two consecutive cropping seasons of 2016/2017. The experiment was laid in a split-plot design with three replications, with the cabbage varieties as main plots and the bio-rational pesticides as subplots. Cabbage plots treated with Bypel 1 and ANKE had the lowest population of Plutella xylostella, Brevicoryne brassicae, Hellula undalis, Bemisia tabaci and Thrips tabaci for both seasons. The control plot consistently had higher pest population in both seasons. There was no detrimental effect of bio-rational pesticides on natural enemies. The bio-rational pesticides-treated plots produced higher yield than control plots. Mean numbers of P. xylostella was higher on KK (0.61, 1.46) compared to Oxylus (0.65, 1.70) in both seasons, respectively. The yield between the cabbage varieties was not significantly different in both seasons, although Bypel 1 (R) and ANKE treated plots generally produced significantly higher yields than the control plot. Yield between both cropping seasons was significantly different (p = 0.039). These findings provide evidence that bio-rational pesticides may offer effective management of the pest complex of cabbage and may be successfully used as an integral part of IPM in Africa as a means to curb the abuse of synthetic insecticides.