oh NO!!!! Banana peels are great treats! As far as I know, they don't spray the trees for anything, but if you're worried, you can wash the banana before peeling it.
My rabbits LOVE...yes LOVE will lay down and BEG for peels. I give them 2inches of a "strip". Loads of vitamins plus fiber.
It might take them a time or two to figure out what it is...but the smell is overwhelming and 90% will try it quickly and like it.