How do you know it's a fungus, Janice? Can you post a photo?
If you dogwood has the dieback that our native dogwoods can suffer from,
you should prune (remove) any infected branches, leaves, and dispose of in the trash. Clean your pruners (wipe with alcohol) when finished.
Good air circulation, keep them watered during dry spells, but if it already has the problem you can't get rid of it. If you decide to plant dogwoods in the future look for disease resistant selections. Here is a link with info about dogwood problems. Hope this helps. http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2003.html
baking soda and water in a garden pressure sprayer. gave new life to my old pink dogwood!!! My old farmer neighbor taught me that one!
Native dogwoods in the woods are dying from a fungus.