How do I treat this infected hydrangeas?
Plant has been covered by dark spots and looks like big bites
Certified GKH Gardening Expert
This looks to be Shot Hole Fungus. This will need to be treated with a fungicide. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This article will give you information on the care of Hydrangea plants: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/growing-hydrangeas-hydrangea-care-guide.htm