I have an apple tree which is at least fifteen years old and produces fruit most years. This year it has developed brown leaves on the lower branches and brown/black places on the bark near the ground. The fruit appears to be developing normally.
I'm in Ontario Canada, which does not allow chemical pesticides, but I spray it with sulphur and insecticidal soap at least a few times in Spring.
What is likely to be the problem and what can I do about it?