Sorghum /Legume Intercrop on Stem Borer Damage and Yield of Sorghumin the South Eastern Dry Areas of Zimbabwe

Abstract

Stem borer (Chilo partellus) is one of the major pest of economic importance which affects sorghum production in the South eastern region of Zimbabwe. The experiment to establish the relationship between stem borer insect suppression by intercropping and grain yield in sorghum and six legumes was conducted under field conditions at Chiredzi Research Station which is in the South Eastern Lowveld (21°01’S, 31°33’E) from 2013 to 2015 cropping seasons. Treatments laid in randomized complete block design and replicated three times consisted of sorghum combined with cowpea, groundnut, pigeon pea and bambara. Monocropped treatments of legumes were cowpea, groundnut, pigeon pea, bambara and two sole sorghum treatments as controls. On one of the controls, an insecticide was applied while the other one remain untreated.  Data collected on stem tunnel length, yield (grain and stover), land equivalent ratio and other pests, indicated that in sorghum sole plots where no chemical was applied, yield was reduced by 28% compared to sole plots where a pesticide was applied. In intercropped combinations of sorghum/groundnut, sorghum/pigeon pea and sorghum/cowpea, an incremental benefit of 10-38% was observed than all other treatments. No benefit was observed in sorghum bambara combinations. Stem borer and aphid had lower thresholds in intercrops. Predators populations recorded in intercrops reduced insect pest density than in monocrops. Thus, these findings indicated that intercropping can form a component of an integrated pest management program.