A method of harvesting crop material comprising gathering the crop material and separating chaff material, and subjecting the chaff material to fragmentation in a cage mill to destroy unwanted seed material contained therein. An agricultural apparatus comprising a mobile apparatus (15) adapted to travel with a harvesting machine (13) during a harvesting operation to receive chaff material produced during the harvesting operation, the mobile apparatus (15) comprising at least one cage mill (21) having a plurality of rotors (51 and 52) for fragmentation of the chaff material to destroy unwanted seed material contained therein. A mill (21) for fragmenting chaff material to destroy unwanted seed material contained therein, the mill comprising a casing (31) defining a milling zone, a rotor means (51 and 52) within the milling zone for performing a milling operation, an inlet (35) for introducing material for reduction into the milling zone, an outlet (37) for removal of material from the milling zone, and means (67) associated with the rotor means (51 and 52) for generating an airflow through the milling zone to assist movement of the material through the milling zone from the inlet to the outlet.
