A system is provided that automatically stops a tractor (7) based on position of a twine arm assembly (51) in a round baler (7). A control system (69) monitors position(s) of the twine arm assembly (51) when an automatic twine-wrapping cycle is initiated. This may include starting a twine arm position monitoring procedure when an initial position change of the twine arms is detected. One or more sensors (87) may be mounted on the baler (7) to detect position characteristics of twine arm assembly (51), which may include presence or absence of the twine arm assembly at certain locations relative to a bale chamber (21) of the baler and/or movement of the twine arm assembly (51). When the control system (69) determines that the twine arm assembly is in an insert preparatory position, the control system sends a tractor halt command which automatically stops tractor (7) at the same time that the wrapping procedure begins.
