Limited translocation of clothianidin seed treatments in corn

The neonicotinoids are a relatively new group of insecticides that have come to dominate the seed treatment market of numerous crops, especially in corn where 79-100% of corn in the US is treated with clothianidin (Poncho®) or thiamethoxam (Cruiser®).  Neonicotinoid seed treatments aim to provide systemic protection from early season, soil-dwelling secondary insect pests.  Given the large-scale use of neonicotinoids in corn and increasing number of neonicotinoid detections in ground and surface waters, a field study was conducted in 2014 and 2015 to determine the amount of seed treatment successfully translocated into a corn plant and by extension, how much is lost to the environment.  In both years, varying rates of seed treatment (control, fungicide only, 0.25 mg, and 1.25 mg of clothianidin per kernel) were sampled three times weekly until 21 DPP (Days Post Plant) with bi-monthly sampling until 61 DPP.  Liquid chromatography mass spectrometry was used to quantify translocated clothianidin by plant region and data was analyzed as a function of time.  In 2014, <1% of the initial clothianidin applications were translocated within the first 17 DPP.  By 12 DPP a maximum of 1.37 and 5.1 µg clothianidin/g plant tissue was reported for the shoot and root regions with both regions decreasing to <0 µg clothianidin/g plant tissue by 19 DPP.  A similar pattern is expected from the 2015 season.