The management of field pests on cowpea (Vigna unguiculata (L.) Walp) using botanicals [Tobacco (Nicotiana tabacum) leaves, neem (Azadirachta indica) leaves, ginger (Zingiber officinale) rhizomes and onion (Allium cepa) Bulbs]

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Theinsecticidal effect of four plant extracts tobacco (Nicotiana tabacum) leaves, neem (Azadirachta indica) leaves, ginger (Zingiber officinale) rhizomes and onion (Allium cepa)bulbs onpests of cowpea was studied. The study was conducted at the Soil and Irrigation Research Centre, Kpong of the University of Ghana, Legon during the minor rainy season (September to mid November, 2012).Aqueous extracts of these botanicals were sprayed on the cowpea plants. A synthetic chemical insecticide,cymethoate, was used as the standard insecticide, and a treatment without any of the extracts (negative control), i.e. just water.The completely randomized design (CRD) was used and each treatment was replicated three times. The effects of these treatments on the population dynamics of the insect pests, total pod weight, total number of pods, number ofdamaged pods and grains, 100 grain weight (g) and grain yield (Kg/ha) were assessed. Results showed that cymethoate effectively controlled field pests of cowpea such as whiteflies, aphids and pod borers during the study. It also resulted in higherweight, pod numbers, and grain yield as well as less number of damaged pods and grains. Neem extract showed no significant difference over the other botanicals for the control of whiteflies, aphids and pod borers and consequently better yield of the cowpea. A hundred (100)grain weight and control of whiteflies at eight weeks after planting (WAP) were significantly different between the treatments (P =0.0120). Although adequate yield was not obtained from ginger, onion and tobacco treated plants, they still showed higher yield compared to the cymethoate. The study also revealed that the two weeks spraying interval employed was effective.Based on the results of the study two key recommendations were made namely, (1) Neem and tobaccoof the botanicals can be used to effectively replace synthetic chemicals as the botanicals are more environmentally safe and less expensive, and adoption of the two-week interval spraying, because of its effectiveness, so as to minimize cost of production.
A thesis submitted to the Department of Theoretical and Applied Biology, College of Science, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the requirement for the award of the degree of Master of Science (Environmental Science), 2014