Answer: Bracken ferns are about as difficult to eradicate as Horsetails (Equisetum). Both spread by underground roots which also serve as storage organs. As long as carbohydrates are stored in the roots, new sprouts will emerge. Foliar herbicides won't really control the bracken, although it will kill the leaves it touches. A better approach is to remove the little sprouts as soon as they emerge, before they unfold and begin the process of photosynthesis. If you're persistent in removing the sprouts the roots will eventually run out of energy and die.
The presence of bracken in a garden doesn't pose a threat to human health; the threat comes to those consuming the leaves and stems.
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