Ground Cover Supplement : GC Supplement - Spray application 2016
10 Sprayer set-up RESEARCH GOES UNDER COVER TO REDUCE DRIFT Shielded sprayers have the double benefit of increasing the number of spraying techniques available to spray operators while also reducing drift potential and crop damage By Dr Andrew Hewitt, Dr Chris O’Donnell, Dr Gary Dorr, Jason Ferguson and Rodolfo Chechetto SPRAY OPERATORS CAN use various approaches to reduce or prevent spray drift, and shielding nozzles is one option to ensure droplets do not blow into the wind. This is because drift is caused when droplets are allowed to move in the air, away from their intended downward trajectory. Putting a hood, shroud, shield or cone over the nozzles or the entire spray boom will ensure droplets do not blow in the wind. One of the commercially available shielded sprayers used by some grain growers in Australia was tested by scientists at the University of Queensland (UQ) using International Organization for Standardization (ISO) protocols. UQ's research in wind tunnel and field studies showed that using a hood over nozzles could reduce drift by more than 90 per cent. Even if the hood was raised to produce a 10-centimetre gap between the bottom of the hood and the canopy or ground, drift reduction was still more than 70 per cent compared with spraying without a hood (Figure 1). This data has been submitted to the Australian Pesticides and Veterinary Medicines Authority with the intention of supporting a large decrease in the downwind buffers (no-spray zones) required when spraying with a shielded sprayer. The wind-tunnel results support earlier field studies conducted by UQ researchers in conjunction with Conservation Farmers Inc on Queensland's Darling Downs. The field work also highlighted some practical considerations of using shielded sprayers within a crop, including: ¢ selecting coarser spray qualities reduced drift and crop damage; ¢ increasing the gap between the shield and the ground by more than 5cm increased drift and crop damage; ¢ increasing travel speed increased drift and crop damage (spraying speeds of about 10 kilometres per hour were generally satisfactory); and ¢ operating into strong headwind conditions increased drift potential. The amount of drift or crop damage observed did not depend on the type of shielded sprayer used; however, it was influenced by how the sprayer was set up and operated. While the drift-reduction potential is significant with a shielded or shrouded sprayer, growers need to carefully consider the registration status of any products before use. □ SOURCE: UNIVERSITY OF QUEENSLAND CENTRE FOR PESTICIDE APPLICATION AND SAFETY FIGURE 1 Reduction in spray drift achieved from a shielded sprayer in wind tunnel and field tests. WT -- 7.2km/h 2cm gap* WT -- 14.4km/h 2cm gap WT -- 21.6km/h 2cm gap WT -- 21.6km/h 10cm gap Field ~7.2km/h Wind tunnel tests Field test Reduction in airborne spray 2m downwind due to shield (%) 100 90 80 70 60 50 40 30 20 10 0 *The gap is between the shield and the ground. Shielded sprayers can minimise crop damage during inter-row spraying and reduce drift potential by more than 90 per cent. PHOTO: SOUTHERN PRECISION For information about nozzle selection and calibration of shielded sprayers, see The Back Pocket Guide: Nozzle selection for boom, band and shielded spraying (www. grdc.com.au/GRDC-BPG- NozzleSelection). FAST FACTS GRDC Research Codes UQ00072, UQ00047 More information: Dr Andrew Hewitt, University of Queensland, email@example.com Note: The inclusion of images in this issue does not imply an endorsement of any particular piece of equipment or a particular spraying technique.
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