Infrared thermography for precise measurement of coverage area of plant leaves with pesticide surfactant formulations

The rational use of surfactant additives in pesticide formulations is an important step toward reducing environmental risks and ensuring food safety. Accurate measurement of spray droplet wetting area and lifetime on leaves is fundamental for optimal surfactant concentration estimation. The high sensitivity of infrared thermography to temperature fluctuations induced by evaporation of thin films facilitates the precise detection of the wetting area. The present study compared the infrared and optical methods for determining the wetting area for surfactant solutions at concentrations ranging from 1 to 5CMC on barley leaves and model surfaces. The findings demonstrate that the infrared thermography detects up to 4.6 times larger wetting area compared to that of measured within the visible spectral range. Furthermore, the lifetime of the wetting film is detected to be 1.5 times longer in the infrared range. This allows a significant correction in the estimation of the optimum surfactant concentration, which is defined as the intersection point of the linear approximations of the dependence of the effective wetted area and the droplet lifetime on surfactant concentration. The range of optimal organosilicon surfactant concentrations obtained in the study on barley leaves for fungicides was found to be the half the range recommended by the manufacturers, while for insecticides it was below the recommended level. The proposed methodology for determining optimal surfactant concentrations based on the infrared thermography can be apply to refine and adapt the regulatory framework for the using of organosilicon surfactants in pesticide solutions.