Quality of spray deposition in a “tendone” vineyard from an air blast sprayer

Apulia (Southern Italy) is the Italian region with the highest production of table grape. The typical vine training system is the “pergolato” or “tendone”, whose main characteristic is the arrangement of the canopy on an unbroken horizontal plane, sustained by a grid of steel wires at 1.7 – 1.8 m above the ground, in turn supported by stakes placed near the vines. Protection of table grapes usually requires about 30 treatments in the period April-November, spraying volume rates in the range 500 – 1000 L ha−1. The correct sprayer setting, with the appropriate selection of the operative parameters such as forward speed, airflow rate, and volume rate, though necessary for all treatments, is of great importance for “tendone” vineyards, because this training system needs particular attention due to its peculiar features. In fact, unlike other crops such as orchards or hedgerow vineyards, the canopy developed on a horizontal plane and the application of plant protection products exclusively from the bottom, make that only the lower side of the canopy is directly exposed to the spray. Furthermore, the subdivision of the canopy into two specialised layers, upper layer with only leaves and lower layer with only grapes, located in some areas only, requires a proper adjustment of the distribution profile of the sprayer when targeted treatments are necessary. Finally, being the production mainly destined for the fresh market, it is necessary to preserve the aesthetic look of the grapes by selecting the nozzles properly. This study reports the main results of a research aimed at evaluating the effects of airflow rate and volume rate on foliar deposits in a “tendone” vineyard when using an air blast sprayer with two counter-rotating fans and anterior intake. Experimental tests were replicated in two phenological stages (full flowering and berry touch), characterised by different Leaf Area Indices (2.21 and 5.83), considering two airflow rates (2.43 and 5.71 m3 s−1), two volume rates (about 335 and 625 L ha−1) and keeping the forward speed constant (1.1 m s−1). Before tests, the sprayer was calibrated using a patternator purposely designed for “tendone” vineyards, achieving a distribution profile in agreement with the vineyard Leaf Area Index pattern. The results showed that foliar deposits were not affected by volume rate at either phenological stage, whereas increasing the airflow rate, they decreased significantly at full flowering (−30% on the most exposed vegetation), and increased significantly at berry touch (+43%).