Crop Protection 124 (2019) 104861 Available online 26 June 2019 0261-2194/© 2019 Elsevier Ltd. All rights reserved. A model to estimate the spray deposit by simulated water sensitive papers Emanuele Cerruto, Giuseppe Manetto, Domenico Longo, Sabina Failla, Rita Papa * Department of Agricoltura, Alimentazione e Ambiente (Di3A), Section of Mechanics and Mechanisation, University of Catania, via Santa Sofa, 100, 95123, Catania, Italy A R T I C L E INFO Keywords: Pesticides Droplet pulverisation Water sensitive papers Image analysis Spray coverage Impact density Stain density ABSTRACT Spray deposit and superfcial coverage play key roles in phytosanitary treatments. Their measurement is a quite complex task that requires adding suitable tracers to the mixture (deposit) and using some artifcial targets (superfcial coverage). With these laboratory tests, unit deposit values, measured in Petri dishes containing sil- icon oil, were correlated with percentage of covered surface, measured with water sensitive papers (WSPs) after spraying a water solution with red Ponceau at 2% concentration. An Albuz ATR 80 hollow cone nozzle was used at the spraying pressures of 0.3, 0.5, 1.0 and 1.5 MPa. The results showed a signifcant correlation between unit deposit d u (μL cm 2 ) and the fraction of covered surface x S (d u ¼ 2:2095⋅x S  0:3473, R 2 ¼ 0.761, p- level < 0.001), that could allow estimating spray deposition from WSP analysis only, even with high values of percentage of superfcial coverage (30%–80%). Moreover, measured data were used to simulate the WSP behaviour. The results of simulation showed that in a practical spray application with a high fraction of su- perfcial coverage, spread factors higher than those reported in WSP datasheets should be considered. 1. Introduction European Directive 2009/128/EC recognises the use of pesticides to have great impact on human health and the environment, therefore promotes the use of approaches or techniques alternative to chemical treatments such as integrated pest management or organic farming (Blandini et al., 2008; Papa et al., 2018). However, when used rationally and carefully, the undoubtable benefts of pesticides, including increased crop and livestock yields, improved food safety, quality of life and longevity, energy use and environmental degradation, must not be forgotten (Cooper and Dobson, 2007). A continuous evolution has affected spraying techniques in the last decades towards precision agriculture: monitoring of spray drift, using sensors to characterise canopies, mapping of crop parameters, and developing variable rate sprayers, are all aspects analysed by researchers and sprayer manufac- turers to make pesticide application more sustainable (Zhang et al., 2002; Gil et al., 2013, 2014; Escol� a et al., 2013; Sharda et al., 2015; Jiao et al., 2016; Grella et al., 2017; Pascuzzi et al., 2018). Spray characteristics affect both the biological effcacy and the environmental impact of every spraying application. Additionally, when a pesticide does not have the desired biological effect on the target an off-target pesticide resistance can be induced and costs for the grower and chemical contamination of the environment can be increased (De Moor et al., 2000). Spray deposit and superfcial coverage play key roles, since the correct deposit assures the proper dose on the target, whereas greater superfcial coverage increases the probability of contact between pest and pesticide. Many factors (active substance, adjuvants, sprayer setting, nozzle types, target features, canopy structure, environmental conditions, etc.) can infuence both aspects, but one of the most important is the spray drop size spectrum (Hewitt, 1997; Matthews, 2004; Nuyttens et al., 2007). In fact, an optimal spectrum maximises the spray effciency as it ensures the transfer of the required dose to the target (leaf, fruit, etc.), minimises off-target losses due to drift and run-off, and reduces operator exposure (Hewitt et al., 1998; Cerruto et al., 2018). There are many droplet size analysers available on the market nowadays, most of which use optical imaging, laser diffraction (LD) and phase Doppler (PD) methods to characterise sprays (Nuyttens et al., 2006). Other custom made solutions are based on digital image analysis (DIA) systems (Lad et al., 2011) or on the use of water sensitive papers, assuming the spread factor is known (ratio between stain diameter and droplet diameter) and the overlap between stains is negligible (Hoff- mann and Hewitt, 2005). In this study droplet size was measured by applying a procedure based on the ISO 5682-1:1996 standard and using a purposely designed test bench (Cerruto et al., 2017). * Corresponding author. E-mail address: rita.papa@gmail.com (R. Papa). Contents lists available at ScienceDirect Crop Protection journal homepage: www.elsevier.com/locate/cropro https://doi.org/10.1016/j.cropro.2019.104861 Received 5 April 2019; Received in revised form 17 June 2019; Accepted 23 June 2019