Apparatus for destroying weed seeds comprising: a housing arranged to be mounted at a location on a combine harvester for receiving from the location a feed material containing separated chaff and weed seeds separated by the combine harvester from harvested crop; a rotor mounted in the housing for rotation about an axis and including rotor surfaces thereon for engaging the feed material and for accelerating the feed material in a direction outwardly from the axis of the rotor; a stator arranged at a location along the direction and including one or more stator surfaces for engaging the weed seeds in the accelerated feed material; said stator and said one or more stator surfaces of the stator being arranged such that the weed seeds impact on said one or more stator surfaces and do not pass through the stator along said direction but instead are rebounded therefrom back toward the rotor; the rotor and stator being arranged such that the weed seeds rebound back and forth between the rotor and the stator to provide a plurality of impacts on the accelerated feed material to destroy at least some of the weed seeds; the apparatus being characterised in that the housing includes a discharge opening for discharge of the feed material after the plurality of impacts; where the discharge opening is at a location different from the stator so that said weed seeds discharged from the rotor through said discharge opening do not pass through the stator; and in that the stator surrounds the axis and wherein the discharge opening is arranged such that the discarded seeds are moved axially from within the stator to the discharge opening. a housing arranged to be mounted at a location on a combine harvester for receiving from the location a feed material containing separated chaff and weed seeds separated by the combine harvester from harvested crop; a rotor mounted in the housing for rotation about an axis and including rotor surfaces thereon for engaging the feed material and for accelerating the feed material in a direction outwardly from the axis of the rotor; a stator arranged at a location along the direction and including one or more stator surfaces for engaging the weed seeds in the accelerated feed material; said stator and said one or more stator surfaces of the stator being arranged such that the weed seeds impact on said one or more stator surfaces and do not pass through the stator along said direction but instead are rebounded therefrom back toward the rotor; the rotor and stator being arranged such that the weed seeds rebound back and forth between the rotor and the stator to provide a plurality of impacts on the accelerated feed material to destroy at least some of the weed seeds; the apparatus being characterised in that the housing includes a discharge opening for discharge of the feed material after the plurality of impacts; where the discharge opening is at a location different from the stator so that said weed seeds discharged from the rotor through said discharge opening do not pass through the stator; and in that the stator surrounds the axis and wherein the discharge opening is arranged such that the discarded seeds are moved axially from within the stator to the discharge opening.