Thank you very much for the good link.
Trouble is, I've already considered the things they mentioned, though. They suggest removing all infected parts of the tree. I would have to cut the tree down, because the entire tree is infected.
Then they say to spray the tree, but I would like to make do without conventional fungicide. Is there an organic fungicide that could help?
Milk? And how do I spray a tree that is approximately 8m tall?
What I can do, and am already doing, is remove the leaves that fall down. I do it every couple of days, since it loses leaves all through summer, not just in fall.
I have been wondering about mulching. The tree sits in the middle of a meadow, with grass growing right up to the trunk. Could this be the problem? Would you mulch over the grass to have a grass-free area around it? Or is this not important for a fully grown and established cherry tree?
I don't have any reason to suspect any nutrient deficiency, other than the tree being sick. We generally have quite fertile soil here, and the tree is well established. But I haven't fertilised it for at least ten years.