Look at the brown spots with a magnifying glass to see if they are scale insects. They will be about 1/16th" and raised up a little. If they are more black and sunken then it is probably a fungus of some kind. If it is scale you will have to spray with Volk Oil or some other oil spray. If it is a fungus then the problem is very dangerous. A county ag agent may be able to recommend a fungicide that will work.