This looks like anthracnose, if you’re in a rainy area, it’s a very common foliar disease on hydrangea. It’s easily treatable with a light spray of fungicide, specifically something listed to control leaf spotting. I use a group 3, 7, and 11 rotation and then sometimes switch it up with a different group (often 9/12 or a copper-based product) in between if I need extra protection. Anthracnose starts as small lesions and moves within the veins of leaves, whereas other leaf spot conditions such as Cercospora (fungal) and Xanthemonas (bacterial) form small dots that almost look like a halo around a dead spot.
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This looks like anthracnose, if you’re in a rainy area, it’s a very common foliar disease on hydrangea. It’s easily treatable with a light spray of fungicide, specifically something listed to control leaf spotting. I use a group 3, 7, and 11 rotation and then sometimes switch it up with a different group (often 9/12 or a copper-based product) in between if I need extra protection. Anthracnose starts as small lesions and moves within the veins of leaves, whereas other leaf spot conditions such as Cercospora (fungal) and Xanthemonas (bacterial) form small dots that almost look like a halo around a dead spot.