International Journal of Agriculture and Forestry 2014, 4(1): 24-33 DOI: 10.5923/j.ijaf.20140401.04 Effect of Plant Density and Weeding Regime on Population and Severity of Aphids (Aphis craccivora Koch) and Foliage Beetles (Ootheca mutabilis Sahl) on Cowpea in Sierra Leone Sheku Max Kanteh 1,* , Johnny E. Norman 1 , Joseph Sherman-Kamara 2 1 Department of Crop Protection, School of Agriculture, Njala University, Freetown, +232, Sierra Leone 2 Department of Agricultural Engineering, School of Technology, Njala University, Private Mail Bag, Freetown, +232, Sierra Leone Abstract Cowpea is one of the major grain legumes grown in Sierra Leone. This trial was conducted in the upland soils of Njala, southern Sierra Leone, in the 2011/2012 cropping season, to determine the effects of plant density and weeding regime on population and severity of aphids and foliage beetles on cowpea. Three plant populations (P 1 = 456,522; P 2 = 239,130 and P 3 = 152,174 plants/ha) and three weeding regimes (no weeding, once at 3 weeks after sowing (WAS) and twice at 3 and 6 WAS) were investigated. The study provides the evidence that- aphids and foliage beetles are better controlled by weeding twice at 3 and 6 WAS, and that planting at lower density (152,174 plants/ha) has the potential to reduce the population of both foliage beetles and aphids. These results have implications for improving cowpea productivity in smallholder farms through the simple manipulation of plant population and weeding regime for the control of aphids and foliage beetles, and probably other cowpea insect pests. Keywords Aphids, Foliage beetles, Plant population, Population, Weeding regime 1. Introduction Cowpea (Vigna unguiculata (L) Walp) is an annual crop that is intensively and widely grown in Africa, and other humid and semi-arid regions of the world[1]. In Sierra Leone, cowpea is the second most important legume crop after groundnut (Arachis hypogea)[2],[3] and many local and improved varieties of the crop are cultivated across the country. Among these, are the popular local varieties like the Tabe (commonly known as black-eyed beans, because of the black colour of its hilium against the background of white testa) mostly grown in Southern Sierra Leone, and the variety Temne which is widely grown in Northern Sierra Leone, as well as other varieties like Holodome/Ladome, and Musia[3],[4]. Among the improved varieties that have been developed and introduced by SLARI (Sierra Leone Agricultural Research Institute) are the Slipea1/TVu 1190, Slipea 2/IT 86D-721 and Slipea 3/IT 86D-1010. Although cowpea can be grown throughout Sierra Leone, studies indicate that Moyamba District (Southern Sierra Leone) is the largest cowpea producing district in the country. * Corresponding author: sheku.kanteh5109@gmail.com (Sheku Max Kanteh) Published online at http://journal.sapub.org/ijaf Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved The popularity of cowpea spans around many parts of Africa due mainly to its importance to many poor households, whose diets are predominantly carbohydrate rich foods with low amounts of protein[5]. Cowpea provides a cheap source of plant protein for many poor households that cannot regularly afford the high cost of popular protein sources like meat, fish and eggs[6]. In terms of chemical composition, the mature grains of cowpea contain about 23 to 25 % protein, 50 to 67 % starch. The crop is also rich in vitamins such as folic acid (important in preventing birth defects); and essential micronutrients such as iron, calcium, and zinc[7]. Besides being a cheap source of protein, several other benefits of cowpea have been reported. These include; food for man and livestock[8],[9],[10], important for controlling soil erosion, improves on soil fertility by providing ground cover and fixing nitrogen into the soil[11],[12],[13], suppresses weeds depending on growth habit, and also positively impacts on the health of women and children[50]. Women particularly value cowpea because it helps them to bridge the hunger months prior to the main cereal (rice) harvest. Trading fresh produce and processed food provide rural and urban women with the opportunity for earning cash income[14],[15],[16], [17]. The stalks are also very important fodder materials when harvested in the dry season (when fresh grass and other fodder materials are not available)[18]. Despite the high economic and nutritional value of