Actually, it's not hard to grow ferns from spores, it just takes careful preparation and patience. If you would like, I can send you spores for lady fern and painted fern for postage. I can email you instructions if you'd like. Send me an email if interested. kms

Too much nitrogen maybe.

Looks like a soil moisture problem to me. Try repotting it in a glazed pot, because terra cotta pots can dry out pretty quickly in hot sunny locations. Some people recommend double-potting for this kind of situation. Also, ferns don't always tolerate chemicals as well as other plants, and spraying with pyrethrin several times a week sounds to me like it would be too much. Is there a recommendation on the pyrethrin container about how often to spray? With ferns, you should figure that the recommended dosage should be cut at least in half, for treating them and also for feeding them. You might be loving it to death...

https://www.minnesotawildflowers.info/fern/lady-fern This site has a lot of information on identification.