A method and apparatus are provided for applying preservative to agricultural crops during baling. More particularly, a baler has a preservative application system and a bale size sensor. The preservative application system has a preservative storage container, a preservative transfer device and an applicator device. The preservative transfer device is in communication with both the storage container and the applicator device to transfer a preservative stored in the storage container to the applicator device. The bale size sensor is in communication with the transfer device so that the transfer device and therefore the application of preservative to the crop can be controlled in response to a bale size sensed by the bale size sensor.