Cationic polymer nanocarriers enhance photostability and foliar retention of Emamectin benzoate for pine wilt disease control

Pine wilt disease, caused by the pine wood nematode ( Bursaphelenchus xylophilus , PWN), represents a significant threat to pine forests ( Pinus koraiensis Siebold & Zucc and Pinus massoniana Lamb) across Asia, particularly in China. While Emamectin benzoate (EB) is commonly employed for pest control, conventional formulations suffer from low efficacy due to photodegradation, poor water dispersibility, and inadequate leaf surface retention—with only 0.1% of applied pesticide reaching the target. This study developed a series of polymer nanocarriers with tunable surface charge properties via reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA). Three nanocarrier variants were fabricated: neutral PTOG-PBMA (POBs), anionic PAA-PBMA (PABs), and cationic PDMA-PBMA (PCBs). All nanocarriers achieved drug loading efficiencies exceeding 65%, with PCBs reaching 78.90%. Critical performance metrics demonstrated the superiority of cationic carriers: following 10 mm simulated rainfall, EB@PCBs retained 80% of applied pesticide on pine needles versus only 42% for neutral and 57% for anionic formulations. Under UV irradiation (365 nm), EB@PCBs maintained 80% of its initial concentration after 5 h, compared to 40% for free EB. In field trials on P. massoniana , EB@PCBs persisted at 0.4% of initial concentration 120 days post-application, whereas conventional EB was depleted within 30 days. These results demonstrate that charge-controlled polymer nanocarriers represent an effective strategy for improving pesticide utilization efficiency and environmental persistence, offering a practical solution for sustainable forest disease management.