ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 69 Number 2
Residual persistence of insecticides on lucerne (Medicago sativa L.)
Lucerne (Medicago sativa L.) grown in the winter season (November-March) was sprayed with endosulfan at 0.4, 0.6 and 0.8 kg a.i. ha-1 and with dimecron and monocrotophos each at 0.16, 0.32 and 0.64 kg a.i. ha-1, 15 days after the first cut and their residues in the crop were determined. Endosulfan at 0.4 and 0.6 kg ha-1 fell below detectable limits by the 21st day and at 0.8 kg ha-1 by the 30th day post-application. At the lower rate (0.4 kg ha-1) it fell below the tolerance limit of 2 ppm within seven days; and with the higher rates, within 14 days, with respective half-life values of 4.10, 4.51 and 3.95 days. Dimecron and monocrotophos fell below the tolerance limit of 0.5 ppm by the 14th day when applied at 0.16 kg ha-1 and on the 21st day post-application when applied at 0.32 and 0.64 kg a.i. ha -1. The lower rate (0.16 kg ha -1) was completely dissipated by the 21st day and both higher rates (0.32 and 0.64 kg ha -1) by the 30th day post-spray, with half-life values of 4.50, 4.04 and 4.06 days for dimecron, and 4.26, 4.00 and 4.47 days for monocrotophos, respectively.
Keywords: Lucerne; Dimecron; Monocrotophos; Endosulfan; Residues; Waiting period