Image analysis of water sensitive paper as a tool for the evaluation of spray distribution of orchard sprayers

Several tests were performed on commercially used orchard sprayers with different types of air discharge systems (conventional, cross flow, directional spouts). The measurements were conducted in a hangar on an apple orchard planted in containers. Pure tab water and water with minerals (Mg, Mn, Zn) were sprayed. Water sensitive paper and blotting paper were put in and around the trees to evaluate the distribution in the canopy by image analysis and/or chemical analysis. The distribution is characterised by a large variability which is partially caused by the random effects of the tree itself. By means of a large number of replicates and correct statistical methods the measurements can be interpreted, but the link between this three dimensional distribution and the adjustment of the sprayer that caused it is very hard to find. Therefore vertical poles, on which water sensitive paper was stuck, were used to further develop an adjustment procedure by means of image analysis. It is possible to determine the spot density, spot size, the histogram of spot sizes and distance between spots. As orchard sprayers are always equipped with air-assistance, it is very important to take the optimisation of the air pattern into account. Therefore the air pattern was also measured. This method of calibration and adjustment of orchard sprayers eliminates human error, maintains a quality standard and provides us with an easy, fast, automated and accurate analysis of the spray quality.