Answer: Leaf spots have many causes. It could indicate a disease or it could be a result of cultural practices. Without seeing the problem, I really can't diagnose it. I would suggest you pinch off the affected leaves. When new leaves appear, carefully inspect them. If they look healthy and do not develop spots, the original problem was cultural in nature. If spots appear on the new leaves, you're dealing with either a fungal or bacterial disease. Again, it's difficult to diagnose without seeing it first hand so I'm at a loss to suggest a control strategy. You might want to put one of the affected leaves into a plastic baggie and take it to your local nursery. Someone there can inspect the leaf and recommend a control strategy.
Best wishes with your hydrangea.
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