Yug

Looks like scale to me. If it is, those brown things are protecting covers for mature females (that are probably getting to hatch even more of them...) while they suck the juices (and the life) out of your nanner. Also, if it is scale, you gotta scrape those things off, and you can kill the young 'crawlers' with ordinary bug spray before they make their own little covers. Once they get under these waxy covers, I don't think anything other than a systemic bug killer will do. A systemic is absorbed by the plant, and permeates its circulatory system; a topical is just for the surface critters.