There's also a big nasty caterpillar thing -- I can't remember the name of the bugger but you can't miss 'em when you find 'em -- that will leave big fuzzy stuff all over your banana plant... But he'd only have taken up residence if the plant had been outside recently. We get them all the time in our banana trees and nothing helps other than finding the culprit by hand. Just in case - check for any leaves which have been 'rolled' or stuck together with the white cottony stuff and peel them apart to check for a vacationing caterpillar.
If you have men who will exclude any of God's creatures from the shelter of compassion and pity, you will have men who will deal likewise with their fellow men. -- St. Francis of Assisi