INITIAL DEPOSITS AND PERSISTENCE OF AZADIRACHTIN IN FIR AND OAK FOLIAGE AFTER SPRAY APPLICATION OF MARGOSAN-O(R) FORMULATION

Foliar deposits and persistence of azadirachtin were investigated afte r spraying 'Margosan-O'(R) formulation at three dosage and volume rate s 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 chromatograp hy (HPLC) at different intervals of time after treatment. Disappearanc e of azadirachtin from both types of foliage was rapid, and the DT5, ( the time required for 50% of the initial concentration to disappear) v alues ranged from 17 to 22 h. The initial azadirachtin concentrations varied widely from 4 to 96 mug g-1 (fresh weight), but the rate consta nts 0.0311 to 0.0414, were not significantly different. The data thus indicated a poor relationship between initial concentrations and the r ate of loss. The influence of spray droplet size and cuticular wax con tent of foliage on persistence of azadirachtin was investigated using both foliar types, and glass microscope slides without and with the fo liar wax coating. Neither the type of surface nor the droplet size inf luenced 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 w ax content than the oak foliage, but the persistance of azadirachtin w as similar in both foliar types.