Residual deposits in green tea shoots and black tea after individual and combined application of propiconazole and copper oxychloride

BACKGROUND: A combination of propiconazole and copper oxychloride is commonly used for controlling blister blight disease caused by the fungus Exobasidium vexans Massee of tea in south India. Field trials were conducted in wet and dry seasons to determine the rate of dissipation of propiconazole and copper oxychloride (COC) in green tea shoots and black tea. High‐performance liquid chromatography was used to quantify propiconazole residues in these matrices. Copper was analysed using atomic absorption spectrometry. RESULTS: The rate of dissipation of propiconazole in both seasons followed first‐order kinetics. Dissipation was faster in the wet than in the dry season. Factors such as rainfall elution and leaf growth dilution lead to faster residual decline in the wet season. However, even in wet season 0.10 mg kg −1 of propiconazole residues were noted in black tea on the seventh day after fungicide application because of its systemic nature. Thus good control over the disease could be achieved. CONCLUSION: The recommended safe harvest interval and half‐life for the combined application of propiconazole and COC from this study is 5.39 and 2.43 days respectively in green tea shoots during the dry season. Moreover, the residues of propiconazole in green tea shoots on the seventh day is the same as the maximum residue limit (MRL) proposed by the European Union (EU), indicating that combined application of the two chemicals does not leave significant residues on seventh day or thereafter. Hence, upon harvest, which is usually between 8 and 10 days after fungicide application, the green tea shoots are safer from fungicide residues and pose less risk to human consumption. Copyright © 2009 Society of Chemical Industry