International audienceWe developed a methodology to perform laboratory studies that approach field conditions. To demonstrate our methods, we used the herbicide mesotrione. Simulated solar light irradiation experiments were conducted on several cuticular wax films. Adjuvants greatly favoured the rate of mesotrione photolysis. Specifically, the photolytic transformation of formulated mesotrione was 15 times faster than that of pure mesotrione. The morphology and composition of the wax films had a greater effect on the photolysis of formulated mesotrione than of pure mesotrione, which formed aggregates on the waxes. This shows the importance of considering the formulation when studying pesticide photolysis on crops. To corroborate our model, we conducted experiments on detached leaves. The rates of photolysis on leaves and on wax films were of the same order of magnitude. Finally, the mesotrione rate of photolysis on leaves is much higher compared with data from the literature in water and on soils. Photolysis is likely to be a fast dissipation process on crops. The photodegradation of pesticide on crops should be systematically evaluated
There is little information about pesticide photostability on plants, especially when considering the effects of the formulation. We evaluated the photostability of a herbicide, mesotrione, on wax films. These surfaces are good systems to mimic the outer layer of the leaf. Within the range of recommended agricultural rates, pure mesotrione half-life on cuticular wax films was between 100 and 160 min. Formulated, the phototransformation rate was multiplied by a factor of 4.8. We assume that the acceleration is mainly due to the surfactants, agents that allow a better spreading of the active ingredient at the leaf surface. Since mesotrione photolysis is a fast process on wax films, we can assume that this process would be significant in the field after treatment.
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