Movement and persistence of [14C]imidacloprid in sugar-beet plants following application to pelleted sugar-beet seed

[ 14 C]Imidacloprid was applied to pelleted seeds of sugar beet which were then grown in pots of field soil. Leaves, roots and soil were analysed at intervals up to 97 days after planting and the distributions of parent compound and of several metabolites were quantified. At the first sampling, 21 days after application, parent imidacloprid was the main compound found in the leaves and its concentration averaged 15.2 μg g -1 fresh weight. By the 25-leaf stage, 97 days after sowing, the concentration of parent compound in the leaves had fallen to an average of 0.5 μg g -1 ; the metabolites and parent compound in the leaves then represented respectively 44.5% and 4.5% of the total applied radioactivity. In the root at 97 days, parent imidacloprid and its metabolites together accounted for only 0.1% of the applied activity, whilst in the soil there was 23% of parent compound and 4% as metabolites. The persistence of both parent imidacloprid and the olefinic metabolite, which has recently been shown to have higher aphicidal activity than the parent imidacloprid, explains the prolonged control of aphids observed with imidacloprid in both glasshouse and field trials.