The Yield and Pest Trade-Off: An Analysis of Insecticide Spray Frequency on the Performance of a Genetically Modified Cowpea in Ghana

A field trial was conducted at two locations in northern Ghana over two successive years to determine the optimal insecticide application timings for mitigating non-lepidopteran pest infestations in a cowpea (Vigna unguiculata (L.) Walp.) variety, Songotra-T. This variety was genetically engineered to resist damage by the Maruca pod borer (MPB) (Maruca vitrata Fab.; Lepidoptera: Crambidae). A split-plot design, with cowpea variety as the main plot factor (Songotra-T vs. Songotra) and insecticide spraying regimes as the sub-plot, was used. Spraying treatments ranged from no spray to three applications at key growth stages (50% flowering, pod initiation, and 50% podding). Data were collected on pest infestation, pod damage, and grain yield. An economic analysis of the spraying regimes tested was performed using yield data. Significant spraying regime effects were observed for non-lepidopteran pests such as whiteflies (p = 0.034), thrips (p = 0.006) and the pod-sucking bugs complex (p < 0.05). Variety effects were mainly significant for MPB infestation and damage to pods. Songotra-T consistently produced approximately 2-fold higher yields than Songotra. Among spraying regimes, two applications at pod initiation and 50% podding resulted in the highest yields, while additional sprays offered no significant advantage. This spraying regime also resulted in a higher return on investment. These findings demonstrate that the adoption of Songotra-T mitigates excessive insecticide use in cowpea production.