This time of year you can give your rabbit's foot fern a haircut. That is, cut of all the fronds. All the existing fronds will die over the summer anyway. I use Cygon at about half strength to treat all my ferns for scale. But any similar systemic should do the trick. First make sure the plant is well watered then mix the pesticide in a big bucket and dunk the plant. It's always easier to avoid getting scale than to treat it. Keep an eye on your garden to head off any infestations. Also, with "Rabbit's foot" good air circulation is essential.
Best of luck.

Cygon has been yanked from the market, I believe.