An agricultural spreader includes at least one delivery conduit that carriesmaterialto be spread from a bin to an exit end of the delivery conduit under theinfluence of air blownthrough the delivery conduit by a fan. A deflector is mounted proximate theexit end of the deliverypipe and deflects the material onto agricultural field in a dispersal area. Aradio frequency (RF)transmitter is disposed to generate an RF signal that passes through thedispersal area. The RFsignal is detectably changed when interacting with the material passingthrough the dispersal area.An RF receiver is disposed to receive the RF signal after the RF signal passesthrough the dispersalarea and provides an output indicative of the RF signal. A controller iscoupled to RF receiver anddetects plugging of the delivery conduit based on the output of the RFreceiver.
