fungicide is rather useless for leave spot fungus after the infection already happens. Cut off severely infected leaves. throw them away. Spray the tree with soap water after rain to clean it up.(water + several drops of just ordinary dish washing detergent) When winter comes, clean all the leaves on the ground, remove old mulch so the fungus does not overwinter in the ground. Cover the ground with fresh mulch. Next year in spring, when the flower comes off, and new leaves comes out, spray the tree with soap water every time after rain, to clean fungus spores away.