MEASURED AND PREDICTED AERIAL SPRAY INTERCEPTION

ABSTRACT. Plant canopies are often the direct or indirect target during aerial spraying. Therefore, there are benefits from understanding and being able to model the factors influencing spray deposition in canopies. Potential benefits from having models that simulate spray interception by canopies include the ability to define application methods and conditions necessary to maximize spray efficiency (i.e., achieve the biological objective with a minimum dose) and to minimize off-target environmental impacts. An experimental study was undertaken to measure spray interception by a discontinuous radiata pine canopy. Two droplet size treatments (volume median diameters of 596 versus 295 m) were applied using a Jet Ranger helicopter, with eight replications of each treatment. Spray deposition was measured on horizontally oriented plastic tubes, which were threaded onto strings located at different layers through a 3 m high canopy. Other measurements included leaf area distribution within the plot and meteorological conditions, with helicopter flight line location and release height determined from a global positioning system. Spray attenuation through the canopy was greater with the smaller droplet size, with only 34 % of the spray reaching the lowest sampling level compared to 46 % with the larger droplets. Predictions of spray attenuation by the optical canopy model in AGDISP did not closely match measured attenuation