A twine cutting apparatus in combination with an automated grass baler having a twine holding reel for feeding wrapping twine to the baled grass. The apparatus has a pivoted knife arm with a first end structured to cooperate with a cam surface for actuating the knife arm to a cutting position and an opposite end for mounting a twine cutting knife. The twine cutting knife is formed with an elongated, serrated cutting edge extending a distance greater than the radius of the twine holding disc presenting an elongated cutting surface to said twine.