A model to estimate the spray deposit by simulated water sensitive papers

Spray deposit and superficial 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 artificial targets (superficial coverage). With these laboratory tests, unit deposit values, measured in Petri dishes containing silicon 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 significant correlation between unit deposit d(u) (mu L cm(-2)) and the fraction of covered surface x(s) (d(u) = 2.2095.x(s) - 0.3473, R-2 = 0.761, p-level < 0.001), that could allow estimating spray deposition from WSP analysis only, even with high values of percentage of superficial 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 superficial coverage, spread factors higher than those reported in WSP datasheets should be considered.