Cheers @hugo7 and @rhb. I think I'll get someone in during the winter to prune the bigger trees and get rid of the cherry. A bad case of powdery mildew seems to be exactly what it is. Lack of airflow is almost certainly a part of the puzzle, so I don't think I'll put another tree in the same spot. I'll replace with a ginkgo tree elsewhere in the garden.
Why? Cherry tree will give you cherries (assuming you beat the pigeons and the squirrels to them), a ginkgo will just make your garden smell awful for a few months every year.
Cheers @hugo7 and @rhb. I think I'll get someone in during the winter to prune the bigger trees and get rid of the cherry. A bad case of powdery mildew seems to be exactly what it is. Lack of airflow is almost certainly a part of the puzzle, so I don't think I'll put another tree in the same spot. I'll replace with a ginkgo tree elsewhere in the garden.