Potential impact of intercropping on major cowpea field pests in Uganda.
Insect pests are perhaps the most important constraint to cowpea (Vigna unguiculata) production. In Uganda, aphids (including Aphis craccivora), thrips (including Megalurothrips sjostedti), pod sucking bugs (including Clavigralla sp. and Leptoglossus sp.) and pod borers (such as Maruca vitrata) are ubiquitous and very devastating, sometimes leading to total crop failure. On-farm studies were conducted at 3 sites in eastern Uganda for three consecutive seasons (during the long rains of 1997, short rains of 1997 and long rains of 1998) to evaluate the use of intercropping as a pest control strategy in cowpea. Two local cowpea cultivars, Ebelat (erect) and Icirikukwai (spreading), were grown as sole crops or intercropped with a local cultivar of green gram (Vigna radiata) or sorghum (Sorghum bicolor) cv. Seredo. Aphids and thrips populations were significantly reduced in the cowpea+sorghum intercrop but were higher in the cowpea+green gram intercrop. In contrast, pod borer and pod sucking bug infestations and their associated damage were significantly higher in the cowpea+sorghum intercrop than in the other cropping systems. These results contradict previous reports and indicate that (a) not all pests are controlled by intercropping, (b) to be effective, intercropping has to be part of a pest management system that involves other control strategies, and (c) choice of a cropping system for integrated pest management should consider the pest profile.