Evaluation of adjuvants for reducing the risk of phytotoxicity in low-volume spray of propiconazole

Unmanned aerial vehicles (UAVs) have been increasingly employed for fungicide applications in plant disease control. However, due to weight limitations, the fungicides sprayed through UAVs must be in low volumes with high concentrations in many instances, which may result in potential phytotoxicity. Here we evaluate the safety of low-volume spray of chemicals on rice plants. The plants were sprayed with propiconazole emulsifiable concentrate (EC) at 250 g/L mixed with various adjuvants and applied at a low volume, which contained the fungicide at concentrations equivalent to or higher than that used in UAV application. The spray adjuvants included YS-20, Biaopu adjuvant, TriTek, Yipinsongzhi, AgriSolv-C100, and Hongyuyan. Potential phytotoxicity on rice plants was examined based on surface tension and crop growth. Additives suitable for a low-volume spray of propiconazole were also assessed on three rice varieties for phytotoxicity. The results showed that after 72 h of fungicide application at 2, 4, and 8 times the recommended dose of 7500 μg/mL for UAV spray, rice leaves exhibited abnormal growth, and the dry weight of rice significantly decreased 21 days after application. Phytotoxicity was evaluated on three rice varieties 5 days after spraying propiconazole EC at 2 × recommended dose with one of the spray adjuvants. The addition of 1% YS-20, Biaopu adjuvant, TriTek, and Yipinsongzhi significantly augmented the phytotoxicity. However, both AgriSolv-C100 and Hongyuyan significantly reduced the comprehensive index of phytotoxicity and, therefore, could be used for UAV applications.