It looks like your hydrangea has fungal disease, possibly Cercospora leaf spot. Remove heavily affected leaves and pick up any that have dropped. Treat with a fungicide. A rainy spring may be the culprit. When watering, avoid wetting the leaves. Detailed articles on the diseases of hydrangea follows: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/common-hydrangea-diseases.htm http://www.tnstate.edu/extension/documents/Foliar%20diseases%20of%20Hydrangea%20FBG%20022916%20G1.pdf
Answered on June 5, 2019
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