The picture shown above is a picture of a Big Leaf Hydrangea leaf that has Cercospora leaf spot. Cercospora leaf spot (Cercospora hydrangea) is a fungal disease. Cercospora hydrangea won't typically threaten the life of a hydrangea. It's more an unattractive nuisance than anything else. The small circular purple, brown or black colored leaf spots from this disease will typically begin to appear during the middle of the summer and will be most prevalent/noticable during the late summer and into early fall. A wet summer with frequent rains, especially frequent afternoon showers, can help spread the disease. Overhead watering can also help spread the disease. The spots typically begin to develop on leaves at the base of the Hydrangea and will work their way up the plant. In order to slow the progression of Cercospora leaf spot, remove leaves that become moderate or heavily spotted, reduce the amount of overhead watering, and/or water the plant by hand at the base. Some heavily spotted leaves may begin to fall off the plant on their own. If this disease becomes a big problem among your hydrangeas, I recommend calling Emerald Acres (978-897-0011) to come out to examine the plant and to apply the appropriate fungicide.