Degradation of Dimethoate and Pirimicarb in Asparagus

Abstract

Dimethoate at 0.25, 0.50, 1.0, and 1.12 kg AI/ha, and pirimicarb at 0.125, 0.25, and 0.50 kg AI/ha were applied as foliar sprays to control the European asparagus aphid, Brachycolus asparagi. Partial conversion of dimethoate to dimethoxon, and pirimicarb to (methylamino)pirimicarb and/or formyl(methyl-amino)pirimicarb occurred in the foliage (fern) as soon as 6–12 h after application. After applications the total residues of both compounds, including their toxic metabolites, decreased by about 90% in 7 days but at a slower rate thereafter. Only traces of pirimicarb (<0.01 ppm) remained 31 days after applications at 0.50 kg AI/ha, and up to 0.03 ppm of dimethoate remained 38 days after applications at 0.50 and 1.0 kg AI/ha. No residue was found above the limit of detection of 0.002 ppm in any asparagus spears following applications of dimethoate and pirimicarb for aphid control. © 1985, American Chemical Society. All rights reserved.