You’ll need to apply a Copper-based fungicidestarting in spring when there are strong buds. Follow the directions on the label.
In the meantime, prune away any infected brances and be thorough about cleaning up and removing all the leaves from yur yard as they fall.
Another problem might be the mulch,,,or how it was applied. Get under there and brush away any mulch and soil away from the trunks a few inches from your trees and shrubs until you find the original soil that the plant came in. Mulching up the trunk or burying the stem too deep hinders the flow of moisture and nutrients from the roos to the branches and leaves above. It is like slowly strangling the plant. I can take a few years but it will eventually kill the shrub or tree. You’ll want to check othe plants that you’ve mulched around as well.