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 surfaces (60, 62) and second surfaces (51, 52) engaging the second material comprising chaff and weed seeds; the first surfaces (60, 62) and second surfaces (51, 52) being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first and second surfaces so that the weed seeds in the second material are devitalized before being spread onto the ground; wherein the weed seed destructor section is mounted at or adjacent the rotary member which provides a drive shaft for the weed seed destructor section; characterized in that there is provided a transfer system to move the second material from a discharge location of the second material to said inlet of said at least one weed seed destructor section (38, 39) wherein said transfer system comprises at least one duct (115, 116) and a blower arrangement (113, 114) for blowing the second material along the duct. 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 surfaces (60, 62) and second surfaces (51, 52) engaging the second material comprising chaff and weed seeds; the first surfaces (60, 62) and second surfaces (51, 52) being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first and second surfaces so that the weed seeds in the second material are devitalized before being spread onto the ground; wherein the weed seed destructor section is mounted at or adjacent the rotary member which provides a drive shaft for the weed seed destructor section; characterized in that there is provided a transfer system to move the second material from a discharge location of the second material to said inlet of said at least one weed seed destructor section (38, 39) wherein said transfer system comprises at least one duct (115, 116) and a blower arrangement (113, 114) for blowing the second material along the duct. an inlet receiving the second material comprising chaff and weed seeds; first surfaces (60, 62) and second surfaces (51, 52) engaging the second material comprising chaff and weed seeds; the first surfaces (60, 62) and second surfaces (51, 52) being mounted for relative rotation such that the second material comprising chaff and weed seeds is impacted between said first and second surfaces so that the weed seeds in the second material are devitalized before being spread onto the ground; wherein the weed seed destructor section is mounted at or adjacent the rotary member which provides a drive shaft for the weed seed destructor section; characterized in that there is provided a transfer system to move the second material from a discharge location of the second material to said inlet of said at least one weed seed destructor section (38, 39) wherein said transfer system comprises at least one duct (115, 116) and a blower arrangement (113, 114) for blowing the second material along the duct.