Efficacy of Trichoderma harzianum against okra jassid (Amrasca biguttula biguttula) (Hemiptera: Cicadellidae): a two-year comparative study of biopesticides

Abstract Background Okra ( Abelmoschus esculentus L.) is widely cultivated in tropical and subtropical regions, where its production is significantly constrained by insect pests. Among them, the jassid ( Amrasca biguttula biguttula ), a polyphagous pest with piercing-sucking mouthparts, causes serious yield losses. The experiments were conducted during the Kharif seasons (June to September) of 2023 and 2024 in the mid-hills of Nepal, using a Randomized Complete Block Design (RCBD) with five treatments and four replications to evaluate the efficacy of different biopesticides against jassid populations. The treatments comprised neem oil (1% EC), Jholmal (a locally prepared organic formulation), Trichoderma harzianum (1 × 10⁸ CFU/ml), Beauveria bassiana (1 × 10⁸ CFU/ml), and an untreated control. Results The highest jassid mortality was recorded in plots treated with T. harzianum , with reductions of 76.72 and 77.26% per plant at 7 days after the third spray during the 2023 and 2024 Kharif seasons, respectively. These reductions were statistically significant ( P < 0.01) compared to the other biopesticide treatments. In 2023, both neem oil and T. harzianum exhibited comparable efficacy after the first and third sprays, while in 2024, their effectiveness aligned during the first and second sprays. B. bassiana showed lower efficacy in the second and third sprays of 2023 but demonstrated improved performance in 2024, consistently reducing jassid populations compared to Jholmal and the control. Yield assessments revealed that T. harzianum -treated plots produced the highest okra yields of 18.73 t/ha in 2023 and 21.25 t/ha in 2024, while the untreated control consistently recorded the lowest yields of 8.75 t/ha and 8.00 t/ha, respectively. Conclusion Among the tested biopesticides, T. harzianum was the most effective in reducing jassid populations and enhancing okra yield under mid-hill conditions. These findings highlight the potential of T. harzianum as an eco-friendly alternative to chemical pesticides, promoting safer food, healthier soils, and sustainable pest management for resource-limited farmers in Nepal’s mid-hill regions.