Abstract
Insecticide treatments involving the soil application of phorate (Thimet) 10 G and disulfoton (Disyston) 5 G for controlling the aphid, Myzus persicae (Sulzer), on potato crops were evaluated for residues at Jalandhar (Punjab) during autumn 1982-83. Treatments were carried out at 1.0 and 1.5 kg a.i. ha-1 according to two protocols (i) single dose applied in furrows at planting and (ii) two equal doses, half applied in furrows at planting and remaining half applied near plant bases just before earthing. The findings revealed that phorate and disulfoton residues in unprocessed (unwashed, unboiled and unpeeled) potatoes treated at 1.0 kg a.i. ha-1 according to the first protocol persisted above the tolerance limits (0.50 mg kg-1 for each compound) up to 60 days; at 1.5 kg a.i. ha-1, residues were above the tolerance limits up to 70 and 60 days, respectively. Phorate and disulfoton residues from 1.0 kg a.i. ha-1 applied according to the second protocol persisted above the tolerance limits for 70/49 and 60/39 days, respectively, in unprocessed potatoes; at 1.5 kg a.i. ha-1 they persisted above the tolerance limits up to 70/49 days. At harvest (90 and 90/69 days after application), residues of both insecticides were below the detection limits in unprocessed potatoes from both levels and protocols. Residues in processed (washed, boiled and peeled) potatoes and in water obtained after cooking were below the tolerance limits at all sampling times.
