For fusarium wilt, look for one side of the leaflets to decline first while the other side remains healthy. Eventually, the entire leaf will wilt. This is caused by an uneven decline in the tissue that conducts nutrients to the leaf. The disease is spread by infected pruning tools and/or the wind. These trees became too high for me to prune so I hired some guys to prune off the dead fronds last fall. I can't say it is their fault for sure but I wouldn't doubt it.
Jim
