Initial deposits and persistence of permethrin in foliage of four tree species, jack pine, white pine, white spruce and trembling aspen, were studied after aerial application of an aqueous tank mix of permethrin at 70 g in 4.0 L/ha, over a mixed plantation forest in Ontario, Canada. Spray was applied using a fixed wing aircraft fitted with Micronair® AU3000 atomizers. Droplets were sampled at ground level using Kromekote® cards, and deposits were collected on glass plates. Foliar lipid content was measured to examine its role on the initial deposit. The trembling aspen foliage, despite its lower wax content, received higher amounts of permethrin (μg/g) than the conifers, thus indicating little relationship between lipid content and initial deposits. Factors such as crown geometry, leaf orientation, size and shape seem to have influenced spray deposition. Little relationship was also indicated between the half-life of duration of persistence and foliar lipid contents.
A laboratory study was conducted to examine the relative importance of three parameters, i.e., foliar wax content, surface area-to-mass ratio, and surface characteristics, on initial deposits on foliage. Permethrin deposits were computed in μg/g and μg/cm2. Surface area-to-mass ratio played a role on foliar concentrations when expressed in μg/g, but not when expressed in μg/g and μg/cm2. The presence of pubescence on aspen leaves, and of serrations on foliage of the two pine species, appeared to have contributed to higher deposits (μg/g and μg/cm2) than those on the smooth spruce needles. The foliar wax content played little role on permethrin deposition, a finding similar to that observed in the field study.