Foliar spray deposition in a “tendone” vineyard as affected by airflow rate, volume rate and vegetative development

The objective of this study was the evaluation of the effect of airflow rate and volume rate on foliar spray deposition in a “tendone” vineyard using an air-assisted sprayer with two counter-rotating fans and anterior intake. Experimental tests were carried out considering two airflow rates (2.43 and 5.71 m3 s−1), two volume rates (335 and 625 L ha−1) and keeping the forward speed constant (1.1 m s−1). To take into account the effect of vegetative development of the vineyard, experiments were replicated in two phenological stages (full flowering and berry touch), characterised by different Leaf Area Indices (2.21 and 5.83). The sprayer was calibrated using a patternator purposely designed for “tendone” vineyards, assuming the vineyard Leaf Area Index (LAI) pattern as a reference. Sprayer calibration was accomplished achieving a close correlation between LAI pattern and the quantity of liquid intercepted by the patternator (coefficients of linear correlation ranged from 0.95 to 0.99, all significant at p < 0.05). Measurements on vines showed that volume rate did not affect foliar spray deposition at either phenological stage, whereas airflow rate had an opposite effect at the two phenological stages. At full flowering, the increase in airflow rate produced a significant decrease in foliar deposit (from 0.986 to 0.693 μL cm−2 on the most exposed vegetation, −30%); on the contrary, at the berry touch growth stage the increase in airflow rate produced a significant increase in foliar deposits (from 0.339 to 0.484 μL cm−2, +43%).