Chemical stability and biological toxicity of some fungicides sprayed on citrus fruits against Spodoptera littoralis (Lepidoptera: Noctuidae) under storage conditions

Abstract

The study investigates the effect of a storage stability test on the degradation of various fungicides. The fungicides tested in the study include Imacid (7.5% LS), which contains Imazalil; Citrocil Plus (27.4% EC), which contains a combination of Imazalil (5% EC) and Orthophenylphenol (22.4% EC); Ortosol (20% EC), which contains Orthophenylphenol; Scholar (23% SC), which contains Fludioxonil; Fruitgard (45% flow SC), which contains Thiabendazole; and Decco (36% SC), which contains Pyrimethanil as an active ingredient. The tested fungicides were stored at 54±2°C for 14 days. During the different storage periods, samples were taken after 7 and 14 days to determine the physical properties of the emulsion concentrate EC, suspension concentrate SC, and solution for seed treatment LS, and evaluate the chemical stability of the active ingredient by HPLC and GC/MS. The results show that the Imazalil, Ortho-phenylphenol, Fludioxonil, Thiabendazole, and Pyrimethanil active ingredients were 7.46, 19.92, 22.62, 44.99, and 35.96%, respectively, and reached 7.24, 19.70, 21.65, 44.76, and 35.88% after 14 days of storage at 54±2oC for Imacid 7.5% LS, Ortosol 20% EC, Scholar 23% SC, Fruitgard 45% flow SC, and Decco 36% SC, respectively. Also, Imazalil 5% active ingredients were 4.99% and reached 4.91% after 14 days of storage at 54 ± 2oC, and Orthophenylphenol 22.45 active ingredients were 22.43% and reached 22.05% after 14 days of storage at 54±2oC for Citrocil Plus 27.4% EC. Additionally, GC/MS was used for the degradation of Imazalil, Orthophenylphenol, Fludioxonil, Thiabendazole, and Pyrimethanil fungicides. From this, it was found that the major degradation products were 1-(2- ethoxy-2-phenylethyl)-1H-imidazole; [(3E)-penta-1,3-dien-3-yl] benzene; 2,2-difluoro-2H-1,3-benzodioxole; (E)-2-(1H-benzimidazol-2- yl) ethene-1-thiol; and 4,6-dimethylpyrimidin-2-amine, respectively. Furthermore, the biological data of the fungicide toxicity test proved its ability to kill larvae at small concentrations, and statistically no significant differences were found between treatments for the 4^th instar larvae of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) that all revealed high toxicity levels, and Imazalil was the most effective one.