Relative Effectiveness of Insecticide Sprays on Insect Damage and Yield of Three Cowpea Cultivars in Swaziland

Abstract

Field trials were carried out for two seasons on the effect of insecticides on insect pests, damage and yield of three cowpea cultivars.During the first season, the preflowering stage of crop growth was found to be infested by Aphis spp, Empoasca spp, Ootheca spp and Epilachna spp, the flowering stage by Megalurothrips sjostedti, Heliothis armigera, Astylus atromaculatus, Coryna kersteni and Mylabris amplectens and the postflowering stage by H. armigera and a number of coreid and pentatomid bugs. Fenthion gave the least protection against pod damage by H. armigera. There were significant increases in the number of harvestable pods per plant with insecticides. There were no significant differences in hull weight and shelling percentage. Grain yield was increased by 96.2 and 109.4% after treatment with dichlorvos and cypermethrin, respectively.In the second season, cypermethrin and monocrotophos were most effective. Cypermethrin reduced the number of pod-sucking bugs by 58%, H. armigera by 93%, while monocrotophos reduced Empoasca spp by 39% and M. sjostedti by 79%. Cypermethrin reduced damage by pod-sucking bugs by 28%, and by H. armigera by 95%. Monocrotophos reduced damage by pod-sucking bugs by 14%, and by H. armigera by 80%. Significant increases in the number of harvestable pods per plant were obtained with monocrotophos and cypermethrin treatments. There were no significant differences between the number of seeds per pod, and the weight of 1000 seed-grains. Grain yield was increased by 55.4% after both cypermethrin and monocrotophos treatment. The application of these insecticides were financially beneficial but the gain was reduced when six sprays were applied. Cypermethrin and monocrotophos are promising insecticides for controlling insect pests on cowpeas.