Adjuvant Effects on Pyraclostrobin and Boscalid Residues, Systemic Movement, and Dietary Risk in Garlic under Field Conditions

Adjuvants are supplemental substances added to pesticide tank mixtures to enhance their efficacy by altering the dispersing, emulsifying, spreading, sticking, and wetting properties of the spray mixture. The goals of this study were an assessment of the effectiveness of pyraclostrobin and boscalid against garlic rust; the fungicide’s dissipation and translocation within plant tissue in the presence of commercial adjuvants Dash ® HC EC; and the validation of an analytical method for concurrently determining boscalid and pyraclostrobin in green garlic and garlic bulbs. Pyraclostrobin and boscalid retention in green garlic and the dietary exposure risks were also evaluated. The adjuvant Dash ® HC EC is an emulsifiable concentrate containing fatty acids, methyl esters, and alkoxylated alcohol–phosphate esters. The test plots were sprayed with the maximum recommended dosage of 400.5 g a.i. ha −1 boscalid and 100.5 g a.i. ha −1 pyraclostrobin. The residues of pyraclostrobin and boscalid in garlic bulb and green garlic samples were determined using a mini-Luke multi-residue solvent extraction method paired with a high-performance liquid chromatography diode array detector (HPLC–DAD). This method is based on the extraction of a homogeneous sample with acetone, petroleum ether, and dichloromethane. Boscalid and pyraclostrobin recoveries in green garlic and garlic bulbs ranged from 71% to 107% on average, with a relative standard deviation (RSD) of 6.8% to 18.1%, and limits of quantification were 0.02 mg/kg. In green garlic and garlic bulbs, boscalid residues ranged from 0.14 to 3.51 mg/kg and pyraclostrobin from lower than LOQ to 1.43 mg/kg, during the experiment. The adjuvant increased the fungicidal efficacy of the fungicides and their retention on green garlic. Although boscalid is considered a nonsystemic fungicide, it showed higher translocation from garlic leaves to garlic bulbs than pyraclostrobin. Regarding the dietary risk assessment, the use of the adjuvant in a tank mixture with boscalid and pyraclostrobin is considered safe 14 days after application, which agrees with the recommended PHI.