Certified GKH Gardening Expert
This is an infection, likely from just a little too much watering.
These shrubs will not need extra water unless there is a severe drought, once established.
It will be best to only water once the soil dries out, very thoroughly, down to about 4 or 5 inches. This will not likely be very often.
From here, a fungicide will be necessary. These articles will help:
Here is an article that will help you to care for the shrub: