Check out page 23 and 24 on the link below.
http://www.ctahr.hawaii.edu/nelsons/...management.pdf
It looks like it could be an Iron toxicity problem (page 24), possibly manganese toxicty (page 23 bottom of picture 7). I am thinking iron though. That is just what it looks like.
Also this one may be of help with your problem as well.
http://www.agroforestry.net/tti/Musa...a-plantain.pdf
Good luck