A harvester having a harvesting structure, an accumulator, and a module builder having a throat. A plurality of meter rollers are positioned to receive crop and transfer crop at a feed rate in cooperation with a beater roller. A feeder belt receives crop from the meter rollers and the beater roller and transfers the crop to the throat. A feed rate control system comprises at least one crop mass flow feedback device providing a crop mass flow feedback signal indicative of crop mass flow. A controller is provided that is in communication with the at least one crop mass flow feedback device and configured to operate in a first mode by lowering the feed rate when the crop mass flow feedback signal indicates a threshold has been reached and by raising the feed rate when the crop mass flow feedback signal indicates the threshold has not been reached.