Efficacy of aqueous leaf extracts and synthetic insecticide on pod-sucking bugs infestation of cowpea (Vigna unguiculata (L.) Walp) in the Guinea Sa-vanna Region of Nigeria

Abstract

Pod-sucking bugs (PSBs) infestation by Ano-plocnemissp./ Riptortussp./Clavigrallasp./Nezaraviridula( Linnaeus) greatly limits cowpea (Vignaunguiculata (L.) Walp) production throughout sub-Saharan Africa. The efficacy of aqueous leaf extracts (ALEs) (5 percent weight/volume concentration) of three botanicals and one synthetic insecticide against PSBs infestation was thus evaluated. The botanicals tested include Aza- dirachtaindicaA. Juss, Chromolaenaodorata (L.) and Ricinuscommunis (L.), whilst the synthetic insecticide was Uppercot 500 EC ( Lambda cyhalothrin 30 g + Dimethoate 250 g ). The effects of these treatments on the number of PSBs/ pods/seeds, pod/seed weight and grain yield were assessed during 2008 and 2009 rainy seasons in Bayo, Borno State, Guinea Savanna region, Nigeria. The number of PSBs was lower on crops treated with Uppercot 500 EC (0.00 - 0.31). This was followed by crops treated with the ALEs ofA.indica/C.odorata (0.31 - 1.33) and R.communis (0.72 - 3.72) than the untreated (3.06 - 5.64) ones.The number of pods/pod weight per plant, seeds/seed weight per pod and total grain yield were generally higher on cowpea crops treated with Uppercot 500 EC (26/17 g, 14/19 g and 1618 kg). This was followed bycrops treated with the ALEs of A.indica/C.odorata (23 - 25/14 - 15 g, 12 - 13/15 g and 1268 - 1310 kg) and R.communis( 21/13 g, 11/14 g and 972 kg) than the untreated (16/9 g, 7/10 g and 312 kg) ones. Although Uppercot 500 EC was most effective inprotecting cowpea against PSBs attack, theALEs of A.indica and C.odorata appreciably protected treated crops against infestation, giving relatively high total grain yield. Both botanical scan thus serve as alternatives to synthetic insecticides for managing PSBs attack on cowpea.