A liquid spray boom having a plurality of spray nozzles and a flow monitoring system for monitoring the liquid flow to each of the spray nozzles. The spray nozzles each have a respective flow metering passage through which liquid to the nozzle passes a magnetic turbine in the metering passage rotatable as an incident to and in relation to liquid directed through the flow metering passage for generating changing magnetic fields, a hall effect sensor associated with each magnetic turbine for sensing the changing magnetic fields, and a control module for receiving signals from the sensor for monitoring the liquid flow to each spray nozzle and providing an alert indication in the event that the flow fails to meet predetermined requirements.