Field Performance and ecological safety of botanical nanoemulsions against sweet potato weevil in Tropical smallholder systems

• Star anise and long pepper nanoemulsions controlled sweet potato weevil. • High adult mortality and reduced oviposition in the field applications. • No major effects on soil health or non-target arthropods. • Botanical nanoemulsions as eco-friendly insecticide alternatives. • Support IPM adoption in smallholder sweet potato farming. This study investigated the effectiveness of two nanoemulsion-based plant hexane extract formulations, S4L0 and S3L1, for managing sweet potato weevils (SPW) under field conditions. The formulations, derived from star anise and long pepper hexane extracts, were tested alongside a synthetic insecticide (imidacloprid) and an untreated control using a randomized complete block design (RCBD) on farmer plots in Sa Kaeo Province, Thailand. Key determination parameters included SPW infestation levels, crop yield, pesticide residue levels, diversity of non-target soil arthropods, and soil physicochemical properties. Field applications of S4L0 and S3L1 reduced SPW infestations to 3.6 ± 4.3 and 11.1 ± 5.0 insects per plant, respectively, significantly lower than in untreated plots (33.9 ± 11.8 insects/plant). No detectable imidacloprid residues were found in tubers treated with S4L0 or S3L1, whereas imidacloprid-treated tubers retained residues of 0.335 and 0.144 ppm at 5 and 7 days after application. Sweet potato yields ranged from 310 to 440 g/plant, with no significant differences among treatments. The untreated plots supported greater diversity and abundance of non-target soil arthropods, while the imidacloprid-treated plots showed the lowest diversity. Soil properties, including bulk density, pH, electrical conductivity, and organic matter content, remained stable across treatments. Overall, S4L0 and S3L1 demonstrated effective pest suppression and minimal environmental impact, highlighting their potential as sustainable alternatives to synthetic insecticides for integrated pest management in sweet potato production.