Assessment of vineyard parameters enabling prediction of the volume effectively applied when using a recycling tunnel sprayer

Tunnel sprayers equipped with spray recycling systems are becoming more and more widespread thanks to their application efficiency. Nevertheless, they can increase risks of point source pollution mainly due to considerable spray mixture amounts that can remain in the tank at the end of the spray application. The effective spray volume applied per vineyard surface unit is in fact difficult to know “a priori”. The goal of this work was to provide the farmer with a simple tool to predict how much spray mixture is necessary to apply on a determined vine surface using a tunnel recycling sprayer in order to minimise the volume remaining in the tank at the end of the spray application. During the summer season 2016, PPP spray application in 153 vineyards located in the north-east of Italy were monitored recording the sprayer settings of the tunnel recycling sprayers employed and the vegetative parameters of the plants. Measurements were performed on 14 cultivars from the phenological stage BBCH-11 to BBCH-81, one-wire or vertical trellised. The sprayer parameters analysed were: number of nozzles, operating pressure, tractor forward speed, sprayed volume (a), recovery volume (b) and volume deposited on leaves (calculated as a-b; assuming that the losses of chemicals are negligible using tunnel sprayers). Dripping from leaves was not observed during the treatments. The vegetative parameters observed were: height and width of the canopy, phenological stage, number of leaves layers, gaps (%), leaf wall area (LWA), tree row volume (TRV), leaf area density and leaf area index (LAI, using point quadrat technique). Results showed a high correlation between canopy height (x) and spray deposition on leaves (y) with a relation y=200•x. The spray deposition on leaves resulted affected also by the different recovery rates. The percentage of gaps in the vegetative wall resulted the main parameter affecting the recovery rate, allowing the formulation of a correction coefficient to better apply the formula in case of poor (high % of gaps) or rich (low % of gaps) vegetation. The equations developed could be usefully applied in order to better define the volume to introduce in the spray tank of a recycling tunnel sprayer according to the vineyard characteristics and the surface to apply so to minimise the amount of spray mixture residue at the end of the application.