A combine harvester comprising: a separation system for separating harvested crop into a first material comprising straw and a second material comprising chaff and weed seeds; a rotary member mounted on the combine harvester at a location thereon to engage the first material comprising the straw, the rotary member including a rotor shaft; at least one weed seed destructor section (38, 39) comprising: an inlet receiving the second material comprising chaff and weed seeds; first (60, 62) and second (51, 52) surfaces engaging the second material comprising chaff and weed seeds; the first (60, 62) and second (51, 52) surfaces being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first (60, 62) and second (51, 52) surfaces; wherein the at least one weed seed destructor section (38, 39) is mounted at or adjacent the rotor shaft of the rotary member which provides a drive shaft for the at least one weed seed destructor section (38, 39); CHARACTERIZED IN THAT at least one of the first (60,62) and second (51,52) surfaces is mounted on the rotor shaft for rotation therewith; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is a rear straw chopper; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is an internal straw chopper. a separation system for separating harvested crop into a first material comprising straw and a second material comprising chaff and weed seeds; a rotary member mounted on the combine harvester at a location thereon to engage the first material comprising the straw, the rotary member including a rotor shaft; at least one weed seed destructor section (38, 39) comprising: an inlet receiving the second material comprising chaff and weed seeds; first (60, 62) and second (51, 52) surfaces engaging the second material comprising chaff and weed seeds; the first (60, 62) and second (51, 52) surfaces being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first (60, 62) and second (51, 52) surfaces; wherein the at least one weed seed destructor section (38, 39) is mounted at or adjacent the rotor shaft of the rotary member which provides a drive shaft for the at least one weed seed destructor section (38, 39); CHARACTERIZED IN THAT at least one of the first (60,62) and second (51,52) surfaces is mounted on the rotor shaft for rotation therewith; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is a rear straw chopper; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is an internal straw chopper. an inlet receiving the second material comprising chaff and weed seeds; first (60, 62) and second (51, 52) surfaces engaging the second material comprising chaff and weed seeds; the first (60, 62) and second (51, 52) surfaces being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first (60, 62) and second (51, 52) surfaces; wherein the at least one weed seed destructor section (38, 39) is mounted at or adjacent the rotor shaft of the rotary member which provides a drive shaft for the at least one weed seed destructor section (38, 39); CHARACTERIZED IN THAT at least one of the first (60,62) and second (51,52) surfaces is mounted on the rotor shaft for rotation therewith; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is a rear straw chopper; OR a rotational axis of the at least one weed seed destructor section (38, 39) is co-axial with the rotor shaft of the rotary member, wherein the rotary member is an internal straw chopper.