Combine harvester comprising an apparatus for destroying weed seeds where the combine harvester comprises a separation system for separating from harvested crop at a first discharge location feed material including chaff and said weed seeds and at a second discharge location straw, the apparatus comprising: a straw chopper section comprising: a chopper housing for mounting at the second location on the combine harvester for receiving from the second discharge location a feed material containing separated straw separated by the combine harvester from harvested crop; a chopper rotor mounted in the housing for chopping the straw for discharge from the housing; and a weed seed destruction section comprising: a housing arranged to be mounted at the first location for receiving from the first discharge location the feed material containing separated chaff and said weed seeds; 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 to cause impacts with the weed seeds; wherein the housing includes a discharge opening for discharge of the feed material after the plurality of impacts; characterized in that the straw chopper section and the weed seed destruction section comprise a common unit in that there is a common drive from the combine harvester to the chopper rotor of the straw chopper section and the rotor of the weed destruction section of the common unit. a chopper housing for mounting at the second location on the combine harvester for receiving from the second discharge location a feed material containing separated straw separated by the combine harvester from harvested crop; a chopper rotor mounted in the housing for chopping the straw for discharge from the housing; and a weed seed destruction section comprising: a housing arranged to be mounted at the first location for receiving from the first discharge location the feed material containing separated chaff and said weed seeds; 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 to cause impacts with the weed seeds; wherein the housing includes a discharge opening for discharge of the feed material after the plurality of impacts; characterized in that the straw chopper section and the weed seed destruction section comprise a common unit in that there is a common drive from the combine harvester to the chopper rotor of the straw chopper section and the rotor of the weed destruction section of the common unit. a housing arranged to be mounted at the first location for receiving from the first discharge location the feed material containing separated chaff and said weed seeds; 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 to cause impacts with the weed seeds; wherein the housing includes a discharge opening for discharge of the feed material after the plurality of impacts; characterized in that the straw chopper section and the weed seed destruction section comprise a common unit in that there is a common drive from the combine harvester to the chopper rotor of the straw chopper section and the rotor of the weed destruction section of the common unit.