THE PERSISTENCE OF INSECTICIDAL CHEMICALS IN SOILS TREATED WITH GRANULAR FORMULATIONS OF DISULFOTON AND THEIR UPTAKE BY POTATO PLANTS

Potatoes were grown from cut seed in Plainfield sand treated in-furrow with disulfoton (Di-Syston 150, 3.36 kg AI/ha) in 1983 and-from whole seed in similarly treated loam in 1991. Soils were contained in 2 m(2 ) field plots. Soil, seed potato and foliage were analyzed for the ins ecticide and its sulfoxide and sulfone metabolites during the 8-12 wk following planting. Disulfoton disappeared at different rates from the two soils (k(sand)=0.024 day(-1), k(loan)=0.056 day(-1)) with partial conversion to the sulfoxide and sulfone in both. Larger quantities of the three insecticidal components were absorbed by the seed potato in the cut-seed/sand combination. The relative amounts of these componen ts in the seed potato also differed between treatments with disulfoton being the largest component of the cut-seed/sand and smallest in the whole-seed/loam. Disulfoton sulfoxide and sulfone were the major insec ticidal components of the foliage and concentrations in the initial fo liage (each ca. 10 ppm) were similar for both treatments. Sulfoxide co ncentrations in the foliage decreased more rapidly than the sulfone an d the decrease in concentration of each of the components was similar for the two treatments.