Q.Problem With Australian Fern Tree
Plant started out healthy and growing fast then fronds in the middle of the plant started turning brown and shriveling. Bottom new growth and top growth was fine. I cut off all the brown branches. Now it looks like the two oldest largest fronds are starting to do the same.
Certified GKH Gardening Expert
The soil may be infected with a bacterial pathogen. I would treat with a fungicide, like copper sulfate. This can help restore the soil.
Otherwise, proper care will ensure the plant's health.
Here are some articles that will help:
https://www.gardeningknowhow.com/ornamental/foliage/tree-ferns/planting-tree-ferns.htm
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm