A sensor detects a characteristic of accumulated crop material and a controller manipulates the speed of a baling chamber in response thereto. The speed of a baling chamber of a variable speed baler is manipulated in response to a characteristic of an accumulated crop material. For example, the height of accumulated crop material in an accumulation area may be detected and the speed of the baling chamber manipulated in response thereto. The rate of growth of the bale may also be determined and used in manipulating the speed of the baling chamber.