| Abstract: | Granular formulations of chlorfenvinphos and phorate were applied to sandyloam soil at 2 kg a.i./ha either broadcast and incorporated to 2.5 cm, broadcast and incorporated at 10 cm or by the bow-wave method along the carrot rows. Depth of incorporation did not influence the rates of residue decline in the soil. Bow-wave applications produced the highest residues in root and foliage and also reduced the rate of oxidation of phorate. 30 weeks after sowing the carrots, all treatments gave the highest residue concentrations in the uppermost 6 cm of carrot root. The peel of carrots grown in the soil treated to a depth of 10 cm contained 88 % and 23 % of the total chlorfenvinphos and phorate residues respectively. Significant differences were found in the residue concentrations in five carrot cultivars treated with chlorfenvinphos and phorate by the bow-wave method at 1.5 kg a.i./ha. The concentrations were inversely correlated with root size so that amounts of insecticide (μg/carrot) were similar in all cultivars. Prolonged growth of cv. Norfolk Giant slightly extended the period of uptake of chlorfenvinphos, but the uptake of phorate was ultimately less than its rate of dissipation. Neither the method of application nor the selection of carrot cultivar extended the period of uptake very greatly but differences which were obtained in residue concentrations in the carrot may become significant in the event of regulatory control of residue levels. |
