Behavior of mixed formulation of metalaxyl and dimethomorph in grape and soil under field conditions.

This study investigates the dissipation and residue of a metalaxyl and dimethomorph mixed formulation in grape and soil. A high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) analytical method was developed to determine the residue of metalaxyl and dimethomorph in grape and soil. The results showed that the average recoveries are in the range of 86.84 percent to 97.30 percent. The dissipation rate of metalaxyl in grape (with half life of 4.9 days) was faster than in soil (with half life of 8.7 days). The dissipation rates of E- and Z-isomers of dimethomorph in grape were almost the same (with half lives of 9.0 and 9.8 days, respectively). However, the dissipation rate of the E-isomer in soil was much faster than that of the Z-isomer (with half lives of 10.3 and 31.5 days, respectively). Moreover, the terminal residue of metalaxyl and dimethomorph were significantly below the available maximum residue limits (MRL). However, a difference was observed between the concentration of the Z- and E-isomers either in grape or soil. The ratio of E-isomer to Z-isomer in grape was higher than in soil, which may due to the different water solubilities and polarities of the two isomers.