Positive effects of an oil adjuvant on efficacy, dissipation and safety of pyrimethanil and boscalid on greenhouse strawberry.

Methylated vegetable oil adjuvants can enhance initial deposition and decrease the required dosages of pesticides sprayed on plants, so an oil adjuvant mixed with fungicides were used to prevent and control gray mold in greenhouse strawberry. As the persistence and dietary exposure risks from fungicides on strawberries after using adjuvants have not been assessed, the efficacy, dissipation and safety of pyrimethanil and boscalid in the presence and absence of a methylated vegetable oil adjuvant were evaluated. To better describe the actual use of fungicides in greenhouse strawberry, twice repeated application of fungicides were conducted follower by an optimized QuEChERS pre-treatment method. When applied at 60% of their recommended dosages with the adjuvant, the efficacy of pyrimethanil and boscalid for gray mold was similar to that shown by the treatment of 100% fungicides in absence of the adjuvant based on Duncan's Multiple-Range test, and their average residues increased to 89.0% and 89.3%, respectively. The adjuvant enhanced the accumulation effect of pyrimethanil residue by 31.7% after repeated applications, and the half-lives were similar (5.2 and 4.2 d). The adjuvant had comparable accumulation effects (1.75 and 1.83) and similar half-lives (5.4 and 5.5 d) for boscalid. In absence of adjuvant, the risk quotients (RQs) of pyrimethanil (0.41 and 0.33) and boscalid (0.49 and 0.63) after twice applications at pre-harvest interval were lower than 1. Adding the methylated vegetable oil adjuvant to fungicides would result in unprolonging half-life and acceptably low dietary exposure risk on strawberries, but lower dosage of fungicides were used.