Influence of Airflow Rate and Forward Speed on the Spray Deposit in Vineyard

The present paper reports the results of some spray application trials carried out in a hedgerow vineyard to assess the influence of airflow rate and forward speed on the foliar deposition, keeping approximately constant the volume application rate. The experimental tests were carried out using an air assisted towed sprayer, fitted with an axial fan and two spray booms equipped with seven turbulence nozzles. A full factorial experimental design with two air flow rates (3.9 and 7.5 m3/s) and three forward speeds (0.9, 1.4, and 2.8 m/s) was adopted, arranged according to a randomised complete block design with four replicates. To take into account the development of the vegetation, the experimental plan was replicated in two phenological stages: "Beginning of berry touch" and "Beginning of ripening". After spray application (just one spray pass for each replicate, delivering a water solution with a food dye as a tracer and a surfactant), 36 leaves were picked on each sample tree, equally shared among three heights and two depths. The foliar deposition was measured by means of a spectrophotometer. The main results show that neither airflow rate, nor forward speed, significantly influence the average foliar deposition in both phenological stages. The overall variability (coefficients of variation) is also almost constant. However, in the second stage, the greater airflow rate improves the foliar deposition on the inside part of the canopy, suggesting the necessity of using not too low air flow rates at full foliage development. Also the forward speed interacts with the sampling zones, showing that at 2.8 m/s the differences among the three heights and the two depths increase, thus suggesting the opportunity to operate in field at 1.4-1.7 m/s.