Looks like toxic salts buildup from too much feed and maybe hard water if it's tap water you use.
Usually kicks in about the middle of flowering. Older leaves get all discoloured and eventually go dry and crispy then it works it's way up the plant until even the little bud leaves dry up too. Done it a few times myself.
Flushing well can almost halt the progress and let you finish up. A long, slow dry and cure will help the bud taste decent.
Good luck.