A method of harvesting crop material includes 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. Also provided is a mobile agricultural apparatus which travels with a harvesting machine during a harvesting operation to receive chaff material produced during the harvesting operation. At least one cage mill having rotors for fragmentation of the chaff material is included with the mobile apparatus, to destroy unwanted seed material contained therein. Such a cage mill includes at least a casing defining a milling zone, a rotor for performing milling, an inlet for introducing material for reduction into the milling zone, an outlet for removal of material from the milling zone, and an airflow through the milling zone to assist movement of the material through the milling zone from the inlet to the outlet.
