Effects of formulation on the run-off of imidacloprid from turf

Imidacloprid is a pesticide often used to control insect pests on residential lawns and golf courses. To investigate its potential to be transported into non‐target aquatic systems by rainfall events, imidacloprid was applied as 5.0 g kg−1 GR and 750 g kg−1 WP to 12 plots planted with bermuda grass set on a 5% slope. The dimethylamine salt of the herbicide 2,4‐D was applied simultaneously to the plots in order to normalize the results to prior trials conducted with other pesticides. At a rate of 2.5 cm h−1, 5‐cm rainfall events were simulated at 24 and 48 h after application and 2.5‐cm events were simulated at 96 and 192 h. After each event water was collected from each plot and analyzed by HPLC for residual insecticide or herbicide. Approximately 1.4% of the insecticide formulated as WP and 1.9% of that formulated as GR was lost from the plots after four run‐off events. Of the total mass lost, 64% and 30% respectively occurred in the first and second run‐off events for the WP formulation versus 75% and 20% for the GR formulation. These values compare with a total mass export of 2.6% for 2,4‐D, of which 95% and 4% of the loss occurred respectively in the first and second run‐off events. The maximum concentration of imidacloprid detected in run‐off water was 0.49 mg litre−1 and occurred during the first run‐off event. © 2002 Society of Chemical Industry