Covering the boom completely with a shroud has been shown to reduce drift. Some companies have developed simple shrouds, while others have improved the aerodynamics of airflow around the shield by placing an airfoil over the shield (Fig. 19).
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| Fig.19. Shrouded booms are highly effective in reducing spray drift. | |
Another advantage of a covered shield is that pesticides can be applied using small droplets that provide better coverage, and the volume of carrier needed can be reduced significantly. One drawback of a completely covered boom or nozzles is that it restricts the operator's ability to visually monitor the nozzles for plugging. However, several companies have developed monitors that detect irregularities in flow rates of individual nozzles. For example, one company has developed a detector that continuously monitors the sound of the spray at each nozzle and warns the operator if nozzle sound levels vary from an ideal sound measurement taken earlier.