Study on the residue of thidiazuron in Cuimi kumquat fruit after spraying thidia-zuron for fruit-protection
Thidiazuron is a commonly used flower and fruit protection agent in the production of Cuimi kum-quat,and its residual risk is unknown.In order to explore the residual and degradation changes of thidiazuron in Cuimi kumquat fruits after application,6 concentrations(5.00,2.50,1.66,1.25,1.00 and 0.83 mg/kg)of thidiazuron mixed with gibberelic acid 13.3 mg/kg and sodium nitrophenolate 9.5 mg/kg were used for crown spraying of Cuimi kumquat from the full-bloom stage with three times continuously spraying at an inter-val of 6-8 days.Fruit samples were collected in 10 batches at 1,3,5,7,9,12,17,25,35 and 105 days after the last spraying for residue detection.The results showed that the thidiazuron residues in the treated fruits at 3 days after the last application were lower than the threshold of maximum residue(0.05 mg/kg)specified in the relevant national standards.The thidiazuron residues in the fruits treated with the commonly used concen-tration of 1.25 mg/kg in production were lower than 0.001 mg/kg at 35 days after the last application.The thidiazuron residues in the fruits treated with the commonly used concentration(1.25 mg/kg)in production were lower than 0.0003 mg/kg at 105 days after the last application and could not be detected.There was no food safety risk in the fruits harvested for marketing at 130 days after the last application.However,the use of 1.0 mg/kg thidiazuron for 3 times or 1.25 mg/kg for 2 times may cause damage to the young fruits,leaves and growth of the trees of Cuimi kumquat.When thidiazuron is used to protect flowers and fruits,it is recommen-ded to use a concentration of about 1.0 mg/kg and spraying for no more than 3 times.The interval between the first and second applications,the second and third applications were 6-8 days,7-10 days,respectively.
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