Comparison between indirect and direct spray drift assessment methods

The drift characteristics of 10 different spray nozzles were tested using three contrasting drift risk assessment means namely; phase Doppler particle analyser (PDPA) laser measurements, wind tunnel measurements (both indirect drift risk assessments) and field drift experiments (direct drift risk assessments). The effect of nozzle size (ISO 02, 03 04 and 06) and nozzle type (standard flat-fan, pre-orifice flat-fan, air-induction) on droplet characteristics, drift potential and field drift were studied. A comparison was made between the results from the indirect and direct measurements to evaluate their potential for predicting the losses occurring from pesticide drift from held crop sprayers. In total, 90 PDPA laser measurements, 46 wind tunnel experiments and 61 field drift experiments were carried out with 10 different spray nozzles at a pressure of 300 kPa. The reference spray application for the field measurements was defined as a Hardi ISO F 110 03 standard flat-fan nozzle at a pressure of 300 kPa with a nozzle or boom height of 0.50 m and a driving speed of 8 km h(-1); conditions that were used for each of the comparative assessments of the different nozzle-pressure combinations. Results showed that with the indirect risk assessments (wind tunnel and PDPA laser measurement), driftability experiments can be made with different spraying systems under directly comparable and repeatable conditions and that both methods are suitable for relative assessments of drift risk. Measuring the proportion of the total volume of droplets smaller than 75 mu m diameter was best suited to represent the drift reduction potential in the field with different nozzle-pressure combinations. This was followed by the wind tunnel approach numerically integrating the measured fallout deposit curve. Both wind tunnel approaches for measuring airborne spray gave inferior results. Based on these indirect drift measurements and a statistical drift prediction equation for the reference spraying, it was possible to come to a realistic estimate of field drift data at a driving speed of 8 km h(-1) and a boom height of 0.50 m. (C) 2009 IAgrE. Published by Elsevier Ltd. All rights reserved.