Most herbicides are sprayed onto fields during application. As the droplets dry, non-volatile lipophilic herbicides spread into the epicuticular waxes present on the leaves and any fruit or vegetables present. Herbicides accumulate in these wax layers before migration to the active biological site, but the herbicides accumulated in or adsorbed on the epicuticular wax are subjected to solar light and may undergo photochemical transformation while in/on this layer. Examining photolysis on plant leaves is complex, since diffusion and transmission of light make experiments on the heterogeneous surfaces of the leaves difficult. In our study of the photolysis of imazethapyr on corn and soybean plants, we removed the epicuticular wax from plant leaves to study the waxes separately. Plants were grown in the Gustavus Adolphus College greenhouse growth chambers allowing the control over factors such as growing temperature, relative humidity, light conditions, and the age of the plants. A design of experiment (DOE) methodology was used to develop a set of experimental conditions to test these growing factors and to build a model for the response variable (photolysis rate) based on the growing factors. Imazethapyr was placed on the epicuticular waxes collected under the various growing conditions, and then samples were irradiated in a Q-Sun Solar Simulator for up to 48 hours. HPLC and LC-MS were used to record photolysis rate constants and identify photoproducts. Initial results suggest that the composition of the waxes do vary as a function of the growth conditions and these physical and chemical changes result in difference in the photodegradation of the absorbed herbicides. In addition to the photochemistry work, microscopy and spectroscopy were used to examine the waxes grown under each set of experimental growing conditions. For comparison and as controls, experiments were also conducted on glass petri dishes and in aqueous solution.

Photolysis of herbicides absorbed to plant surfaces: Imazethapyr on corn and soybean waxes

250th National Meeting (2015)

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