Measurements of atmospheric deterioration of citrus spray oils
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Autoxidative deterioration of three commercial mineral spray oils was studied by measuring oxygen absorption under atmospheric conditions and by an accelerated method in the laboratory. The outdoor experiment showed an absorption of 0.02-0.25 moles of oxygen per mole of oil during the first 5 days, which increased to 0.13-0.42 moles after 20 days of exposure. The oxygen absorption was accompanied by separation of insoluble tar-like substances. The relative rates of the autoxidation of the three oils were found to be in agreement with their tendency to cause excessive fruit drop.
Accelerated autoxidation was performed under controlled conditions of temperature, light spectrum and relative light intensity; it was accomplished in several hours and gave approximately the same results as the outdoor experiment. The accelerated procedure is closely correlated with the atmospheric one and thus is suitable as a routine test for spray oils, for mineral oil fraction or formu-lations, and for mixtures of oils with other pesticides.
Key WordsSpray oil citrus autoxidation
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