Persistence and mobility of granular insecticides in an organic soil following furrow application for onion maggot control

Abstract

Ethion, fonofos, fensulfothion, carbofuran, or chlorpyrifos was applied as a commercial granular formulation at rates equivalent to 2.24, 1.12, 1.12, 1.68, and 1.68 kg AI ha^‐1, respectively, to furrows in 33 x 26 x 11 cm volumes of an organic soil. Treated soils were kept in a greenhouse and subjected to 4 different watering schedules ("normal”;, 0.5, 1.0 and 1.5 mL cm^‐2). Persistence and movement of the insecticides was measured by glc analysis of soil cores taken directly from the treated furrow and from each side in duplicate samples at 2, 4, 6, 8, and 10 wk after treatment. In‐furrow cores taken 10 wk after treatment were sectioned and the top, middle and bottom sections were analyzed separately. Water not retained by the soil was collected and analyzed also. Overall persistence was: ethion ? chlorpyrifos ? fonofos >> carbofuran ? fensulfothion. Car‐bofuran and fensulfothion disappearance was slightly faster in the 2 wetter soils, ca. 50% the concentration present in the drier soils at 10 wk. Lateral or vertical movement was not significant in any insecticide‐water combination. Unretained water did not contain significant concentrations of insecticides.

Ethion, fonofos, carbofuran, chlorpyrifos, or chlorfenvinphos granular was applied to furrows of seeded onions at rates equivalent to 2.24, 1.12, 1.68, 1.68, and 1.18 kg AI ha^‐1, respectively, in an organic soil contained in duplicate field microplots (2.2 x 0.9 m). Insecticide residues were determined by glc analysis of the harvested onions and of soil samples collected after cultivation in the fall and the following spring. Plots were treated with insecticide and seeded with onions for 3 successive yr. Residues in the soil after 3 yr were in the order ethion (7.6 ppm) >> fonofos ? chlorpyrifos ? chlorfenvinphos >> carbofuran (<0.01 ppm). Residues in the onions were not greater than 0.01 ppm.

Key words:

• Ethion
• Fonofos
• Fensulfothion
• Carbofuran
• Chlorpyrifos
• Chlorfenvinphos
• Degradation
• Kinetics
• Moisture