Spray deposition in “tendone” vineyards when using a pneumatic electrostatic sprayer

The objective of this study was to evaluate the effect of the electrostatic charge on foliar spray deposition in an Apulian “tendone” vineyard using an innovative pneumatic electrostatic sprayer. The sprayer was fitted with nozzles that linked the pneumatic atomization of the liquid, obtained using compressed air, to the electrostatic induction charge, thereby producing a stream of charged fine droplets. Furthermore, the sprayer was designed for low volume treatments, and the experimentation was carried out during a phenological stage with high leaf density to evaluate the performance of the machine under particularly challenging operative conditions. The sprayer was studied at three forward speeds (4, 5, and 6 km/h), and gave poor deposition inside the canopy, whether or not the electrostatic system was activated. Forward speed did not significantly affect the mean foliar spray deposition, whereas activation of the electrostatic system significantly increased the deposit only on the layer of foliage nearest to the sprayer (lower layer), but had no effect on deposition on the layer of foliage inside the canopy (upper layer). The ratio between the deposits on the two layers (lower:upper) was 6.5:1 when the electrostatic system was switched off, and 9.0:1 when it was switched on. However, this behaviour may allow targeted treatments on grapes, such as Plant Protection Products (PPP) or bio growth stimulants. Furthermore, the small droplets produced by the machine are suitable for table grape protection because the droplets do not mark the grapes, which would reduce the quality of the product and its commercial value.