Full Length Research Paper

Effects of insecticide spray application on insect pest infestation and yield of cowpea (Vigna unguiculata (L.) Walp.) in the Transkei, South Africa

W. D. Dzemo¹, A. S. Niba¹* and J. A. N. Asiwe²

¹Department of Zoology, Walter Sisulu University, P/B X1 NMD Mthatha 5117, South Africa.

²Agricultural Research Council (ARC), Small Grain Institute, Private Bag X29, Bethlehem 9700, South Africa.

*Corresponding author. E-mail: Aniba@wsu.ac.za. Tel: +27 47 5022894. Fax: +27 47 5022725.

Accepted 26 February, 2010

   Abstract

Field studies were conducted during the 2008 - 2009 cropping season to determine the minimal insecticide application which can reduce cowpea yield losses on the field due to insect pest infestations in the Transkei region of South Africa. Treatments consisted of five cowpea varieties and four regimes of insecticide spray which were laid out with a split-plot experimental design with four replications. Observations were taken on the incidence of major insect pests, cowpea pod and seed damage by insects as well as growth and yield parameters of the cowpea varieties. Results showed that spray regimes had significant effects on insect population counts, pod and seed damage and consequently on cowpea yield parameters. Application of insecticide once each at flower budding and early podding significantly reduced pod borers and pod-sucking bugs infestations by 44 and 56%, respectively, compared to the untreated control. Application of insecticide, once at flower budding, early podding and pod filling significantly reduced pod and seed damage, resulting in substantial increase in number of pods, pod weight and seed weight per plant, and also number of seeds per pod of cowpea compared to the untreated control. This study provides information on the incidence of major insect pests of cowpea as well as the minimum insecticide control intervention necessary for effectively reducing cowpea yield losses on the field. Two insecticide spray regimes (once at flowering and podding) significantly reduced insect population and damage of cowpea.

Key words: Cowpea, insecticide spray, insect pests, yield.