Hi BB I'm no banana expert, but have they been exposed to frost or a cold spell, or are they in a shady or windy spot? There are a few tropical experts on this forum (Pete?, Steve?, Nathan? where are you?)& many helpful people who I'm sure can help you alot more than I can. If you can post a pic that would help too.
I find they go through the summer months without problem, the older leaves do go sort of blackish and dead and then peal away from the stem but the new leaves should be nice and green, other than that I would say maybe over watering? then again they like plenty of water when actively growing....puzzler any chance of a pic?
THANKS EVERYONE FOR REPLIES MY PLANTS ARE JUST YOUNG AND I KEEP THEM ON THE KITCHEN WINDOW SILL I`M SORRY I HAVE NO PHOTO