I live in central Newfoundland and have a sick tree. Last July all the leaves turned black and fell off. It developed new growth, though it was sparse. This spring the new growth appeared normal, if a little sparse, but now all the leaves are falling off again, and are yellowish with black/dark brown spots. Is this a bug or a mold or leaf blight? What can I do? The tree is almost 50 feet, much too big to spray. Thanks!