Initial deposits and persistence of azadirachtin in fir and oak foliage after spray application of ‘Margosan‐O’® formulation

Abstract

AbstractFoliar deposits and persistence of azadirachtin were investigated after spraying ‘Margosan‐O’® formulation at three dosage and volume rates on to balsam fir and oak seedlings in a laboratory chamber. Droplet‐size spectra and deposits were assessed using artificial samplers, and foliar residues were measured by high‐performance liquid chromatography (HPLC) at different intervals of time after treatment. Disappearance of azadirachtin from both types of foliage was rapid, and the DT50 (the time required for 50% of the initial concentration to disappear) values ranged from 17 to 22 h. The initial azadirachtin concentrations varied widely from 4 to 96 μg g−1 (fresh weight), but the rate constants 0.0311 to 0.0414, were not significantly different. The data thus indicated a poor relationship between initial concentrations and the rate of loss.The influence of spray droplet size and cuticular wax content of foliage on persistence of azadirachtin was investigated using both foliar types, and glass microscope slides without and with the foliar wax coating. Neither the type of surface nor the droplet size influenced the persistence. The rate of azadirachtin loss from the glass slides was faster than from both types of foliage, and was unaffected by the presence of wax coating. The fir foliage had higher cuticular wax content than the oak foliage, but the persistance of azadirachtin was similar in both foliar types.