Answer: What you're finding on the undersides of your fern fronds are spores, and they're perfectly normal and natural. Instead of producing flowers and seeds like other perennials, ferns reproduce from spores. Once spores develop and are released, the frond may die. Some ferns die down during the winter months and other ferns remain green all year around. Sounds as though your fern goes dormant (rests) for a few months before it develops new fronds. (Or dies because you've used an insecticide formulated for vegetables and it's too strong for your fern.) Rather than scraping off the spores, allow them to mature and spill onto the soil below and you'll have lots of new baby ferns. Cut the fronds off as they die, but continue to water the plant in the usual manner. After the roots have rested they will produce new foliage. In the meantime, new baby ferns may sprout.
Keep the veggie insecticide away from your fern and it may remain green all year around!
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