Dissipation and Mobility of Permethrin in the Field with Repeated Applications Under Tropical Conditions
Studies on persistence, mobility and the effect of repeated application of permethrin on its half‐life were carried out under field conditions. The half‐life of permethrin in the top 20 cm of the soil increased from 11.5 to 23.6 days as the application rates increased from 35 to 140 g ha− 1. Induced by heavier rainfall, more residues moved downward in trial 2 than in trial 1. Repeated applications enhanced degradation rates and mobility of permethrin in the soil. The residue level in the 0–5‐cm layer was reduced at day 28 after 17 consecutive applications to a level lower than after 5 applications. The half‐life of permethrin was reduced from 15.9 days to 11.2 days after 5 and 17 applications, respectively. The residue reached the 15–20 cm layer much earlier (approximately 3 days after treatment) in soil that received 17 applications as compared to those with two applications.