The dissipation of lambda‐cyhalothrin from cotton production systems

Abstract

The dissipation of the pyrethroid, lambda‐cyhalothrin [α‐cyano‐3‐phenoxybenzyl‐3‐(2‐chloro‐3,3,3‐trifluoroprop‐l‐enyl)‐2,2‐dimethyl cyclopropanecarboxylate] was studied in sterile buffer solution at two different pH values. It was observed that during the four week period, lambda‐cyhalothrin was degraded in buffer solution at pH 9, with a half‐life of 53 days, but not at pH 7. Isomerization of this compound was also observed at both pH values, but the rate was much greater at pH 9. The dissipation of this pyrethroid in cotton‐growing soil and on cotton plants was studied under laboratory and field conditions. Laboratory experiments indicated that degradation of this compound is mainly biological. Increasing soil water content increased its dissipation rate. The half‐lives of this compound in the incubated soil with different water contents were in the range of 15–37 days under laboratory conditions and about 18 days under field conditions. Dissipation rates from cotton plants under glasshouse and field conditions differed markedly, with half‐lives of 93 and 4 days respectively. Isomerization of this pyrethroid in soil and cotton plants was observed, a factor that should be considered by analysts.