Enhancing the Efficacy of Biocontrol Agents (BCAs) in Suppressing Plant Diseases Through Conservation Agriculture Practices: Effect of Trichoderma spp. in controlling Alternaria Leaf Spot in Common Beans

Alternaria Leaf Spot (ALS), caused by Alternaria alternata, is a major fungal disease affecting common bean (Phaseolus vulgaris) thereby leading to significant yield losses and threatening food security. The overreliance on chemical fungicides for disease control has raised concerns due to their associated health risks and environmental degradation. This study aimed to evaluate the efficacy of Trichoderma spp., a known biological control agent, in suppressing ALS through Conservation Agriculture (CA) systems, with the goal of offering a sustainable alternative to synthetic fungicides. A 2×3 factorial split-plot design was used to investigate the interaction between three treatment types (Trichoderma, Ramsulf fungicide, and untreated control) and two management systems (CA with mulch and conventional bare soil) across 18 plots. Data on disease incidence (DI), disease severity (DSI), percent severity index (PSI), and yield were collected over three weeks and analyzed using ANOVA in Minitab. The results revealed that both Trichoderma and Ramsulf significantly reduced DI and DSI compared to the control, with Trichoderma achieving a 29.2% reduction in DI and a 71.9% reduction in DSI. Notably, the CA system enhanced the performance of Trichoderma, with the lowest disease severity observed in CA mulched plots treated with Trichoderma (DSI = 1.60, PSI = 17.78%). Furthermore, Trichoderma-treated plots had substantially lower pesticide residue levels (<0.000083 mg/g), meeting international safety standards and outperforming Ramsulf in residue reduction. Yield performance was also highest in CA mulched plots treated with Trichoderma, indicating both agronomic and economic benefits. This study demonstrates that integrating Trichoderma spp. with CA practices not only provides effective disease control comparable to chemical fungicides but also promotes environmental health, food safety, and crop productivity. The findings support the adoption of ecological farming strategies that combine biocontrol and sustainable land management thus offering a scalable model for disease management in smallholder systems. Future research should explore multi-season trials and economic evaluations to further validate these promising results.