A system to monitor fluids in nozzles (40) and an agricultural spray system is disclosed. The system to monitor fluids comprises: a spray nozzle (40) configured to release a fluid according to a desired flow rate； a thermal sensor (50) positioned in a fluid path of the fluid inside the spray nozzle (40)； an electronic feedback circuit designed to attempt to maintain at least one of a current through the thermal sensor (50) and a voltage across the thermal sensor (50)； wherein a measured value of at least one of the current and the voltage different from a target value indicates a change in resistance of the thermal sensor (50)； and wherein a range of the measured value is correlated with an actual flow rate of the fluid. The agricultural spray system comprising: a spray boom (30) mounted on a motor vehicle； a fluid distribution pipe (42) mounted to the spray boom (30)； spray nozzles (40) mounted along the fluid distribution pipe (42) to receive a fluid, wherein one or more of the spray nozzles (40) comprises a system to monitor fluids in nozzles (40).
