Studies On Dispersion Of Thiamethoxam/Lambda-cyhalothrin CS And Diafenthiuron CS And The Control Effect In Tea Garden

Tea is an important economic crop in China. Pesticides were applied to control the diseases and pests in tea farming. However, the unscientific application of pesticides will cause the pesticide residues in tea products over limit, and reduce the yield and quality of tea. So how to apply pesticides scientifically and safely on tea tree become to a problem which need to research and explore with constantly.In this paper, Thiamethoxam/Lambda-Cyhalothrin and Diafenthiuron were applied in tea farm, and then the fresh tea leaves were plucked randomly from each treatment replication at different time intervals [0(1 hour after last spraying), 1, 3, 5, 7, 10 and 15day]. The pesticide residues in the fresh tea leaves was extract with acetonitrile, and cleaning with Florsil and Activated Carbon, the Lambda-Cyhalothrin was detected by GC-ECD while the Thiamethoxam and Diafenthiuron were detected by LC to study the residual degradation dynamics on tea. The combined application of two pesticides were used to control the pests in tea farm. The Thiamethoxam/Lambda-Cyhalothrin was applied after 8d the Diafenthiuron application. The efficacy to pests and the influence to tea growth of the pesticides were evaluated by investigating the number of pests and measuring the length, width, thickness, count, weight of the tea leaves.The main results were as follows:1 The residues analysis methods of Lambda-Cyhalothrin, Thiamethoxam and Diafenthiuron on tea fresh leaf were established, and when these three pesticides were spiked as 0.01-1mg/kg levels in fresh tea leaves, the average recoveries of the methods were between 89.63% ~ 93.74%、85.55% ~ 90.55% and 93.74% ~ 85.55%, respectively, with relative standard deviations(RSDs) of3.91% ~ 7.61%, 4.24% ~ 8.37% and 5.62%~7.30%. All the limit of quantification(LOQ) of there three pesticides were less than 0.01mg/kg, the accuracy and precision of the method have reached the residue analysis methods requirements.2 The residual degradation dynamics of Lambda-Cyhalothrin, Thiamethoxam and Diafenthiuron in tea farm was studied. The results show that the half-life of these three pesticides were 2.70 ~ 3.00 d, 4.48 d ~ 4.50 d and 3.70 ~ 4.57 d, respectively. The pesticides were degraded more than 90% in 15 days from application. And the degradation of three pesticides in fresh tea leaves could be described by first-order kinetics equation. The residues of Lambda-Cyhalothrin,Thiamethoxam and Diafenthiuron in dry tea leaves after applied 15 days were lower than the MRL in China and Japan.3 The combined application pesticides controlled pests in tea farm effectively. The control effects on tea leafhopper and tea geometrid were 77.77% ~ 87.65% and 98.35% ~ 99.25%,respectively. The growth of tea leaves was been surveyed after pesticides applied 23 days.Compared with the contorl, the weight of 100 buts increased 26.90% by the combined application of the pesticides, and the length, width, thickness of tea leaves were increased significantly by the combined application of the pesticides.