You cannot apply a broad leaf herbicide over ferns, without killing the ferns.

Thanks Rhizo,

I was afraid of that. Back to the knees for hand weeding. Sigh!!

George

This is an old thread, but do not agree with the answer. Not all the chemicals to control broadleef weeds affect ferns e.g. 2-4-D has little effect. Look up the chemicals which are used to control ferns, and if they are mentioned in a broad leaf control, don't use it. Stick to a specific chemical and experiment on a small area to prove it works on weeds and does not affect the ferns. Start with 2-4D.