Effect of two formulations on the decline curves and residue levels of rotenone in cabbage and soil under field conditions

•Behavior of two new rotenone formulations, SC and WDG, has been studied.•Half-lives of rotenone in SC and WDG formulations are less than 4 d.•Terminal residues are below MRL in China, higher than in EU after 6 d PHI.•The type of formulations has a significant effect on terminal residue.

The dissipation and residue levels of rotenone with suspension concentrate (SC) as well as water dispersible granule (WDG) formulations in cabbage and soil were investigated under field conditions. The decline curves of rotenone residues in cabbage and soil corresponded with first-order kinetics. The dissipation rate of rotenone in cabbage was faster than that in soil. The half-lives of the SC formulations in cabbage and soil were 1.14 d to 1.85 d and 2.26 d to 3.98 d, respectively. For the WDG formulation, the values were 1.33 d to 1.96 d and 2.41 d to 3.38 d. Less spraying, lower dosage, and longer pre-harvest intervals could reduce terminal residue levels. Terminal residues below the MRL (0.5 mg kg−1) were achieved after pre-harvest intervals of 3 d at either once (45 g a.i. ha−1) or twice (90 g a.i. ha−1) the recommended dosage. The different dissipation processes of rotenone in cabbage and soil under field conditions could be attributed to the different climate and soil properties, and the types of formulation had no apparent effect on half-life. Formulation type affected the initial concentrations and finally led to different terminal residues. Prolonged pre-harvest intervals are necessary to ensure that the products are sufficiently safe for consumption.