Residue and dissipation dynamics of pyraclostrobin in waxberry (Myrica rubra) and soil

To investigate the dissipation and residues of pyraclostrobin in waxberry (Myrica rubra) and soil, the residues and dissipation dynamics of pyraclostrobin in waxberry and soil were conducted in field trials at Zhejiang, Chongqing, Hunan and Yunnan in 2017. An effective method was developed for the determination of pyraclostrobin residue in waxberry and soil. The samples were extracted with acetonitrile and water, purified with primary secondary amine (PSA) and C₁₈, and detected by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that all the correlation coefficient of calibration curves were higher than 0.99 in the range from 0.0005 to 0.5 mg/L. At the spiked levels of 0.01, 0.5 and 5.0 mg/kg, the average recoveries of pyraclostrobin in waxberry were from 92% to 97% with the relative standard deviations (RSD) ranging from 1.0% to 2.7%. The average recoveries of pyraclostrobin in soil were from 86% to 96% with the RSD ranging from 1.5% to 4.1%. The limit of quantitation (LOQ) of pyraclostrobin in waxberry and soil was 0.01 mg/kg. The field trial results showed that the dissipation equations of pyraclostrobin in waxberry and soil samples fit the first-order kinetics equation. The half-lives in waxberry were 6.6-11.8 d, and the half-lives in soil were 5.0-11.1 d. The 60% pyraclostrobin + mancozeb WG was sprayed at 800 and 1200 mg/kg on waxberry for 3-4 times and samples were collected 21, 25 and 28 d after the last application. The maximum final residue of pyraclostrobin in the waxberry was 1.4 mg/kg, which was below the maximum residual limit (3.0 mg/kg) in China. It is recommendated that the security interval of 60% pyraclostrobin + mancozeb WG for waxberry is 21 days, when it is sprayed for 3 times at the dose of 800 mg/kg with the sprayed interval 7 d.