Field evaluation of tephrosia vogelii and dichapetalum cymosum crude botanical extracts in the control of fall armyworm (Spodoptera Frugiperda J. E Smith) in Zimbabwe

Abstract

Fall armyworm (Spodoptera frugiperda J.E Smith) which invaded Africa in 2016, is inflicting serious damage on crops particularly staple maize thereby threatening food security. This is further worsened by little information on host -pest relationship in the new environment. Response to the pest has mainly relied on synthetic pesticides which are usually out of reach of small farmers and has paid little regard to economic threshold levels. The objectives of this experiment were to evaluate the efficacy of locally available botanicals (T. vogelii and D. cymosum) on fall armyworm in maize. The research also sought to understand the host-pest complex by studying the relationship between damage indices and yield. The experiment was set up as a Completely Randomised Block Design with five treatments of two botanicals, their mixture, a positive and negative control replicated three times. Data were analysed using GenStat version 16. Deltamethrin and pirimiphos-methyl (ecoterex) was consistent and outperformed all the other treatments on damage indices, plant height and fresh cob weight. On the same note, the botanicals outperformed the negative control on leaf damage, plant height and damaged cobs. Dichapetalum treatment had similar performance as ecoterex on yield while Tephrosia + Dichapetalum had similar effect on damaged cobs. The regression analysis showed a negative relationship between damage indices (leaf damage score, percentage plants affected and percentage barren stalks) and yield. The regression model explained the general relationship (P= 0.003) but analysis of individual predictors indicated that only barren stalks was significant (P = 0.03). Though the botanicals were better than the negative control, their performance was not consistent. As such, farmers can use the botanicals under study as integrative components of crop protection as they did not produce consistent results on their own. Reliance on percentage infestation and leaf damage scoring in implementing control measure, predicting economic thresholds and yield reduction may not produce accurate results. Key words Spodoptera frugiperda leaf damage botanicals synthetic pesticides cob damage