Variations in insect-induced fruit damage and yield of okra Abelmoschus esculentus after insecticide treatments at different phenological growth stages

Several phytophagous insect pests are known to attack okra, Abelmoschus esculentus (L.) Moench in the field. However, information on the fruit-damaging species and the effective time for insecticide application(s) is still scanty. Field experiments were conducted in 2017 and 2018 to identify the categories of damage inflicted on okra fruits by associated insect herbivores and to ascertain the phenological growth stage in which insecticide applications will significantly reduce insect-induced fruit damage and improve crop yield. Treatments consisted of the application of Cypermethrin 20EC at two-week intervals on NHAe47-4 variety of okra during the vegetative stage (VGS), reproductive stage (RGS), VGS + RGS, and no spray (control). The setup was in randomized complete blocks with four replicates. Results showed that incisions, feeding lesions, localized discolorations, bumps, distortions, and larval exit holes are the major fruit damage symptoms caused by field insect pests of okra. Generally, fruit damage was significantly reduced, while fruit yield was higher in plots that received insecticide sprays at vegetative and reproductive stages than in the control. Fruit production increased significantly by 56.9–69.6% and 57.7–73.1% in 2017 and 2018 in treated plots compared to control, respectively. Fruit damage was reduced by 37.5-92.5% (2017) and 44.6–94.6% (2018), and fresh fruit yield of okra was increased by [58.8–75.0% (2017) and 63.1-76.1% (2018)]. We conclude that an effective field management strategy for insects associated with okra fruit damage should include potent control tactics at the crop's vegetative and reproductive growth stages.