COMPARATIVE ASSESSMENT OF PRE- AND POST-EMERGENCE APPLICATIONS OF CASSAVA MILL EFFLUENT FOR WEED MANAGEMENT
Keywords:
Bio-herbicide, cyanogenic compounds, Cassava processing waste, Weed control efficiencyAbstract
Weed management in smallholder and low-input farming systems is constrained by the cost, environmental risks, and declining efficacy of synthetic herbicides. Cassava mill effluent (CME), a cassava-processing by-product rich in cyanogenic compounds, has potential for weed control, but its application strategy and persistence are poorly understood. This study evaluated the efficacy of CME applied as a pre-emergence soil treatment and as a post-emergence foliar spray for weed control. A screen-house experiment was conducted using a Completely Randomised Design with three replicates. CME was applied at rates equivalent to 6, 12, 18, and 24 g CN ha⁻¹, alongside an untreated control, either before weed emergence or after weed establishment. Weed density, species richness, fresh and dry biomass, and weed control efficiency (WCE) were assessed over two successive weed flushes. Pre-emergence soil application of CME showed no significant effects on weed density, biomass, or species richness across both flushes, indicating limited effectiveness under soil-applied conditions. In contrast, post-emergence foliar application significantly reduced weed density from 1188 to 280 plants m2, fresh weight from 3927 to 495 g m2, , and dry weight from 825 to 118 g m2 during the first weed flush. The highest level of weed control was achieved at 24 g CN ha⁻¹ applied post-emergence, with weed control efficiency peaking at 85.9%. No significant weed suppression was observed during the second flush, suggesting limited residual activity of CME. The study concludes that CME functions as a short-lived bioherbicide when applied post-emergence, with effectiveness dependent on direct contact with weed foliage. Its low persistence implies minimal risk to subsequent crops, supporting its suitability for sustainable and integrated weed management systems. Therefore, repeated post-emergence applications of CME at 24 g CN ha⁻¹, or its integration with other weed control methods, are recommended to enhance long-term weed management effectiveness.
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