Initial deposits, persistence and degradation kinetics of the insect growth regulator, diflubenzuron, in some terrestrial matrices following simulated aerial application

Abstract

Abstract Initial deposits, persistence and degradation of difiubenzuron [1‐(4‐chlorophenyl)‐3‐(2,6‐difluorobenzoyl) urea] in spruce foliage, forest litter and soil were studied under forestry conditions by applying the chemical as a simulated aerial spray in acetone (DAc) and in fuel oil:Arotex® mixture (DFAr), each at 90 g Al (active ingredient) in 18 L/ha. The residues of diflubenzuron in the substrates were determined by gas‐liquid chromatography, after derivatization as its dimethyl analog. The highest concentrations of the chemical in foliage, litter and soil were 30.6, 4.60 and 3.20 μg/g (fresh wt.), detected at 1 h post‐application of the DFAr formulation. The corresponding concentrations in the three substrates were comparatively low for the DAc formulation. With both formulations, residues found in the substrates correlated well with the droplet density and deposit levels observed on the Kromekote® card/glass plate units placed at ground level. In soil and litter, the residues decreased more rapidly than those in foliage. The half‐lives (d) for the chemical in foliage, litter and soil for the DAc formulation were 9.30, 8.36 and 7.49, respectively; corresponding values for the DFAr formulation were 12.8,7.34 and 6.52 d. Forty‐five days after application, the residue levels in foliage were 3.9 and 0.80 μg/g (fresh wt.) for the DFAr and DAc formulations, respectively; the corresponding residue level for litter for the DFAr formulation was 0.10 μg/g. Litter sprayed with DAc and soil sprayed with DAc and DFAr formulations did not contain detectable levels of the chemical on the 45th day post‐application.