The use of Bracken as a packaging product in, (I think ) Rose plant delivery was stopped as it was carcinogenic. So not suitable for use as a dried mulch but could be composted. The best way to kill the plant is to damage but not actually cut off the fronds, if possible run it over. There is a bracken specific herbicide, useful where it’s growing through other plants, Asulox, containing asulam, also kills docks in grassland.
pete