Formulating Copper Nanoparticles into Oil Dispersion for Better Delivery and Favorable Efficacy on Rice Bacterial Blight

Bacterial blight is a plant disease that severely threatens the yield and quality of rice. Copper agents are a kind of efficient pesticide to protect plants from bacterial diseases. Due to the hydrophobicity of rice leaves, the deposition of pesticides on these leaves is not always satisfactory. In this study, copper nanoparticles (Cu2O and CuS) were formulated into oil dispersions (OD) using renewable vegetable oil as solvent, and the potential strategies for enhancing the efficiency of pesticide delivery and increasing deposition of droplets on the surface of hydrophobic leaves were investigated. The OD of Cu2O (Cu2O-OD) was superior to those of wettable powder and suspension concentrate in terms of wetting and spreading performance. The contact angle of droplets was reduced by over 40°, while the retention amount was increased by 1.38–2.65 times, and droplet bouncing and splashing were significantly inhibited. The microbial growth curve test indicated that the bioactivity of Cu2O-OD increased 2.5 times. In the safety test, Cu2O-OD and CuS-OD were found to be safer than zinc thiazole (an effective bactericide registered for the management of rice bacterial blight). Copper nanoparticles were appropriate to be formulated into OD; both Cu2O-OD and CuS-OD have the advantages of low contact angle, high adhesion, and retention on hydrophobic leaves, which make up for the limitations of Cu2O and CuS themselves and have broad application prospects.