Cultivar and insecticide spraying time effects on cowpea insect pests and grain yield in northern Ghana

Abstract

Insecticide application is the recommended practice for control of insect pests on cowpea (Vigna unquiculata (L) Walp). However, these have negative effects on humans and the environment, apart from being costly for resource-poor farmers. This study aimed at identifying appropriate combinations of cultivar and insecticide spraying times for the management of economically important insect pests of cowpea in northern Ghana. The study was conducted in two successive rainy seasons at two locations situated in the Sudan and Guinea Savannah zones of northern Ghana. The experimental layout was a complete randomized split plot design with main-plots consisting of different numbers and timing of insecticide application and sub-plots consisting of 6 different cowpea cultivars. Data collected included insect pest abundances, components of yield and yield. Thrips (Megalurothrips sjostedti Trybom), legume pod borer (Maruca vitrata Fabricius) and a complex of pod-sucking bugs (PSBs) were the dominant insect pests. Their abundance and damage were not significantly different between the untreated control and cowpea sprayed once at 50% flowering stage. In contrast, protecting cowpea with either two (i.e., flower bud initiation and early podding) or three rounds of insecticide sprays (i.e., bud initiation, 50% flowering and 50% podding) significantly lowered insect pest abundance and increased grain yield. Apart from the farmer's cultivar which was susceptible to pest attacks, the improved ones showed variable levels of tolerance to the different pest categories. Combining at least two rounds of insecticide sprays with any improved variety suppressed pest populations and increase cowpea grain yield. Keywords: Cowpea, Insecticide treatments, Savannahs, Yield, Damage levels, Integrated pest management