Controlled-release biochar-based hydrogel microspheres for enhanced effectiveness and prolonged activity of clothianidin against sugarcane pests

SA@BC@CTD hydrogel microspheres were successfully prepared. • High drug loading (16.15%) and encapsulation efficiency (91.68%) were achieved. • The formulation exhibited environmentally responsive controlled release. • Long-term pest control effectiveness was maintained for up to 60 days. • Reduced and delayed acute toxicity to earthworms compared with conventional CTD was observed. Sugarcane ( Saccharum officinarum L.) constitutes a major sugar crop and renewable bioenergy feedstock that plays a vital role in shaping the global agricultural economy and energy systems. However, sugarcane production is significantly threatened by pest infestations, which reduce yield and long-term sustainability levels. Although chemical pesticides are widely employed for pest control, their excessive use has caused significant environmental concerns and potential risks to human and ecological health. To address these challenges, nanobiochar (BC)-based clothianidin (CTD) composite hydrogel microspheres (SA@BC@CTD) were developed via the use of sodium alginate (SA) as the matrix and BC as a functional carrier via Ca²⁺ crosslinking. The release behavior, insecticidal performance, crop safety, and environmental risks of the prepared microspheres were comprehensively characterized through laboratory, pot, and field experiments. Compared with SA@CTD, SA@BC@CTD exhibited a stable three-dimensional porous structure, with a drug loading content of 16.15 ± 0.53% and an encapsulation efficiency of 91.68 ± 1.72%, representing increases of 87.40% and 16.70%, respectively. CTD release was significantly affected by pH and ionic strength, with optimal controlled-release behavior under neutral conditions (pH of 7) and high ionic strength (1 mol/L NaCl), with the duration of sustained release exceeding 96 h. The results of indoor bioassays demonstrated that compared with SA@CTD, SA@BC@CTD exhibited significantly increased concentration-dependent insecticidal activity against Spodoptera frugiperda Smith (third-instar larvae) and Chilo sacchariphagus Bojer‌ (second-instar larvae). The results of pot experiments demonstrated that the application of SA@BC@CTD significantly enhanced sugarcane growth (plant height: 134.05 ± 24.17 cm; fresh weight: 431.35 ± 46.63 g at 60 d) while maintaining high insecticidal effectiveness (mortality rates of 35.12 ± 3.26% for S. frugiperda and 37.64 ± 3.52% for C. sacchariphagus at 60 d). This effect could be attributed to the sustained release of CTD and its enhanced translocation to aerial tissues, as indicated by a leaf transfer coefficient of 0.33 ± 0.02 at 60 d. Field trials confirmed that the use of SA@BC@CTD provided long-term control of dead sugarcane heart (81.59 ± 4.22%) at 60 d, thereby significantly outperforming conventional CTD granules. Moreover, acute toxicity tests using Eisenia fetida Savigny showed reduced toxicity compared with conventional CTD. In conclusion, this study provides a feasible strategy for sustained-release pesticide formulations with prolonged efficacy, enabling reduced pesticide use and sustainable sugarcane cultivation. Download: Download high-res image (141KB) Download: Download full-size image