The ferns have not had Brown Spot ever in 20 years. The ferns in past years are abundant, large and lush. What should I do to prepare for next year?
Unfortunately, I do not see any “brown spot” on your ferns. I am wondering if what you are observing are the sori (plural of sorus), a yellow-brown cluster of structures that produce sporangia (plural of spores). It is found usually on the lower (abaxial) surface of the fern leaves. Fronds are composed of a leaf blade and petiole (leaf stalk). The leaf size, shape and complexity of dissection varies from species to species. Sterile fronds lack spores, are green, and do most of the photosynthesizing. The fertile part of a fern can be very similar to, or totally unlike, the sterile part, depending on the genus or species.
Ferns do not require much maintenance other than cutting back the fronds when they have turned brown in the fall. You can divide your ferns every few years in the spring in order to maintain healthy growth and prevent overcrowding.