little bumps that can be rubbed off sounds like scale insects. They might also be Aphids. If you have a hand lens you should be able to identify them. Aphids are obviously insects while scale are immobile lumps.
Your tree will be losing it's leaves soon. Perhaps you need not do anything other than destroy the fallen leaves so they do not reinfect your plant next spring. You could also try a dormant oil spray to kill any possible eggs that may be present.