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The aim of the study was to assess the possibility of using water sensitive papers (WSP) to estimate the amount of deposit on the target when varying the spray characteristics. To identify the main quantities influencing the deposit, some simplifying hypotheses were applied to simulate WSP behaviour: log-normal distribution of the diameters of the drops and circular stains randomly placed on the images. A very large number (4704) of images of WSPs were produced by means of simulation. The images were obtained by simulating drops of different arithmetic mean diameter (40-300 μm), different coefficient of variation (0.1-1.5), and different percentage of covered surface (2-100%, not considering overlaps). These images were considered to be effective WSP images and then analysed using image processing software in order to measure the percentage of covered surface, the number of particles, and the area of each particle; the deposit was then calculated. These data were correlated with those used to produce the images, varying the spray characteristics. As far as the drop populations are concerned, a classification based on the volume median diameter only should be avoided, especially in case of high variability. This, in fact, results in classifying sprays with very low arithmetic mean diameter as extremely or ultra coarse. The WSP image analysis shows that the relation between simulated and computed percentage of covered surface is independent of the type of spray, whereas impact density and unitary deposit can be estimated from the computed percentage of covered surface only if the spray characteristics (arithmetic mean and coefficient of variation of the drop diameters) are known. These data can be estimated by analysing the particles on the WSP images. The results of a validation test show good agreement between simulated and computed deposits, testified by a high (0.93) coefficient of determination.

Aim of the study is to assess the possibility to use water sensitive papers to estimate, beside the superficial coverage, also the amount of deposit on the target at varying the spray features. To point out the main quantities influencing the deposit, the behaviour of the water sensitive papers was simulated by assuming some simplifying hypotheses: log-normal distribution of the diameter population of the drops and circular spots. Several images (630) of water sensitive papers, sprayed with drops of different mean diameter (from 100 up to 500 μm), constant coefficient of variation (0.50), and theoretical percentage of covered surface ranging from 10 up to 100%, were produced by means of simulation. These images were considered as effective water sensitive paper images and then analysed by means of an image processing software. The correlations between measured and effective values were studied and they allowed for an estimate of deposit and spray features from the image data. This implies that the analysis of the water sensitive paper images allows the determination of more complex parameters such as the unitary deposit and the impact density, all data strictly related to the efficacy of a phytosanitary treatment.