Diazinon in apple orchards: Dissipation from vegetation and exposure to non-target organisms

Comprehensive residue determinations were made for leaves, grass, and other biota from apple orchards following repeated applications of diazinon (D-z-n(R) 50W). Orchards in Washington and Pennsylvania served as study areas representing different climatic zones and agricultural practices. Mean diazinon application was measured to be 3.0 to 3.1 kg AI/ha in over 230 samples from orchards in the states studied. Vegetation was collected in four orchards from each state on days 0, 4, and 12 post application. Diazinon dissipation from vegetation was measured following repeated applications in Washington and Pennsylvania orchards. Residue dissipation was described by a simple exponential function r >0.93). The individual degradation rates measured in each field provide a distribution of diazinon presence that can be used for probablistic exposure assessments. It is also worthwhile to note that no significant exposure to earthworms or avian species occurred more than 4 days post application. Significant exposure to these non-target species occurred when at least 19% of applied residue remained on vegetation.