Knapsack sprayer calibration: perception of swath width and problems of computation

Abstract A trial was conducted to evaluate people's perception and measurement of the swath widths produced by a spray nozzle held at three different heights above the ground whilst spraying. Nineteen individuals, having no previous experience of pesticide application, consistently underestimated the swath width compared with measurements made by three experienced spray operators. Half of another 22 participants failed to calculate correctly the amount of pesticide required to spray a 1 ha field, but all but one individual successfully made up a 20% solution of a hypothetical pesticide mixture. The results suggest that more detail on the measurement of swath widths is required in instruction manuals, and that training courses need to take particular account of the inability of many operators to perform simple calculations.