INSECTICIDE RESIDUE IN SOIL, POTATOES, CARROTS, BEETS, RUTABAGAS, WHEAT PLANTS AND GRAIN FOLLOWING TREATMENT OF THE SOIL WITH DYFONATE

Dyfonate (O-ethyl S-phenyl ethylphosphonodithioate) was incorporated into soil at the rate of 5.6 or 11.2 kg/ha as granules or emulsifiable concentrate and its persistence in soil and its absorption by potatoes (Solanum tuberosum L.), carrots (Daucus carota L.), beets (Beta vulgaris L.), rutabagas (Brassica napobrassica (L.) Mill), and wheat (Triticum aestivum L.) plants were studied in four locations in Saskatchewan. Proportionately more residue persisted in the soil from the higher rate of application. About 33–35% of the Dyfonate applied as granules at the lower rate remained in the soil 4 mo after application, whereas about 38–41% remained from the emulsifiable concentrate. At the end of the same period, 52–64% of the granules applied at the higher rate remained in the soil as compared to 50–71% from the emulsifiable concentrate. Only 3–10% of the applied chemical remained in the soil 29 mo after application. No residue of dyfoxon (O-ethyl S-phenyl ethylphosphonothioate) was detected in any soil. Potatoes, beets and rutabagas harvested 4 mo after application of Dyfonate had little (0.005 to 0.009 ppm) or no detectable (less than 0.005 ppm) residue, irrespective of the rate of application. Wheat seedlings had between 0.01–0.07 ppm Dyfonate and little or no detectable residue in the more mature plant or in the grain. Carrots grown in soil treated at the lower rate had about 0.35 and 0.04 ppm Dyfonate and dyfoxon, respectively, and at the higher rate, 0.81 and 0.06 ppm. About 77–94% of the residues in carrots could be removed by peeling.