S, S, S-Tributyl Phosphorotrithioate Washoff and Dissipation of Foliar Residues

Individual mature cotton leaves were treated with [14C]tribufos and subjected to intense rainfall during a 15-day post-treatment interval. Ten centimeters of washoff from each leaf was collected as 1-cm fractions. Radioactivity in each fraction and the amount remaining on each washed leaf was quantified at each of six time intervals. Washoff decreased over time and was found to be negligible after 3 days post-treatment compared to the amount of tributes which was applied. The first 1-cm fraction of rainfall was found to be the most effective at washing foliar residues of tribufos from treated leaves at all time intervals. Unwashed treated leaves were also analyzed to determine the foliar dissipation of tribufos over the course of the study. Tribufos dissipated with a foliar half-life of 20.0 days (R2 = 0.70). The greenhouse test procedure was shown to be a useful method to quantify foliar washoff potential.