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A generic approach to improving spray coverage


Abstract

Studies were conducted in wind tunnels and vineyards to show the performance of various factors that affect spray coverage on different canopy regions and losses through runoff and drift. These factors included different combinations of nozzles, adjuvants, electrostatic charging, recapture systems, air targeting, barrier vegetation and netting. The best system for any given application will depend on the target. For example, for herbicide applications, coarser sprays can be achieved using the droplet size data, whereas for foliar-applied sprays, the finer sprays can be optimally directed to their target including inner canopy areas using lateral air or radial air with deflector air at the top. Recapture-recycling sprayers offer an additional benefit to those listed above in that the small amount of spray that misses the target is caught and can be reused, reducing losses to almost zero. Electrostatically-charged sprays offer excellent coverage on all leaf surfaces but can drift under adverse conditions due to the very small size of the droplets. Barriers are very effective at capturing most drift, so electrostatic sprays may be safer where there are barriers downwind of the vineyard.

The data from this project support new national regulations that will offer applicators greater choice to achieve smaller no-spray buffers than they would otherwise have had, with previous regulatory reliance on the U.S. AgDRIFT model. By introducing an Australian reference sprayer, this project provided a bridge for comparison of all Australian sprayer performance data, through this project and any future research, to gain credit in the upcoming new national drift regulatory scheme. The droplet size and drift potential data from the wind tunnel are provided in a format ready for loading into a novel spray calculator coverage and drift performance App following the finalisation of this scheme, which is expected by the end of 2017.

The research showed that canopy wall area-based calibration is superior to ground area-based calibration.

Simple tools are available for the assessment of spray performance in vineyards, such as fluorescent tracer dyes and image analysis. Appropriate resolution of at least 4800 DPI is required for the latter.

Summary

To ensure that grape growers can achieve good coverage and maximum efficacy with agricultural plant-protection products and to assess Drift Reduction Technologies (DRTs) to minimise spray drift potential.